Investigation of Microstructure of Disordered Colloidal Systems by
r
Small-Angle Scattering
by
USETT
OCT 2 9
Wei-Shan Chiang
uNTIUEEssa
2014
LIBRARIES
B.S., Chemical Engineering (2006), National Tsing Hua University
M.S., Chemical Engineering (2008), National Tsing Hua University
Submitted to the Department of Nuclear Science and Engineering
In partial fulfilment of the requirements for the degree of
DOCTOR OF PHILOSOPHY IN NUCLEAR SCIENCE AND ENGINEERING
at the
MASSACHUSETTS INSTITUTE OF TECHNOLOGY
September 2014
Massachusetts Institute of Technology 2014. All rights reserved.
Signature redacted
Department of Nuclear Science and Engineering
August 22, 2014
Signature redacted
Certified by
Sow-Hsin Chen
Professor Emeritus of Nuclear Science and Engineering
Thesis Supervisor
Signature redacted
Certified by
Sidney Yip
Professor Emeritus of Nuclear Science and Engineering
and Materials Science and Engineering
Thesis Reader
Signature redacted
Accepted by
Mujid S. Kazimi
TEPCO Professor of Nuclear Engineering
Chair, Department Committee on Graduate Students
2
Investigation of Microstructure of Disordered Colloidal Systems by
Small-Angle Scattering
by
Wei-Shan Chiang
Submitted to the Department of Nuclear Science and Engineering
on August 22, 2014, in partial fulfilment of the requirements for the degree of
DOCTOR OF PHILOSOPHY IN NUCLEAR SCIENCE AND ENGINEERING
Abstract
Small-angle scattering (SAS) has been widely applied to study the microstructure of colloidal
systems. Although colloids cover a wide range of materials, in general they can simply be
viewed as basic building particles arranging themselves, according to their interaction, in a
continuous medium. In this study, three seemingly very different systems were investigated
under various conditions. They are the calcium-silicate-hydrate (C-S-H) gel, magnesium-silicatehydrate (M-S-H) gel, and micellar solution formed by Pluronics triblock copolymers.
C-S-H is the main binding phase of ordinary Portland cements. An elaborate analytical model for
the form factor of C-S-H basic building particles was established for the first time. This model
has ability to integrate two different models together by taking two different limits of the form
factor formula. Essential structural parameters of C-S-H gels prepared at various conditions were
extracted through model fitting. It was found in this study that microstructure of C-S-H gels
changes from continuous planar pore structure to discrete colloidal structure when increasing
water content or adding methylhydroxyethyl cellulose additive. Open microstructure or small
globule size leads to higher flowability or facilitates the extrusion process as macroscopic
properties.
Much attention has been paid recently to the MgO-based green cements due to the little CO 2
generated during their production process compared with the ordinary cements. However, the
poor mechanical properties prevent them from implementing widescale use. This current study
on microstructure of both C-S-H and M-S-H gels indicates that the primary unit at the nanoscale
level of C-S-H to be a multilayer disk-like globule, whereas for M-S-H it is a spherical globule.
This prominent difference at the nanoscale also reflects in gel structure at micrometer lengthscale. The surface contact between the basic particles found in C-S-H gels leads to better
mechanical properties than M-S-H gels which interact through point contact. This study
therefore gives essential insight to design future robust and eco-friendly binders.
Pluronics is a class of amphiphilic copolymers which aggregate to form micelle particles in water.
Small-angle neutron scattering contrast variation measurements were conducted to extract the
microstructure, especially the solvent distribution within the micelle particles, under several
conditions. It is suggested in this study that high water content found in the micelles formed by
short copolymer chains but same PO/EO ratio promotes composition fluctuation within the
micelles and in turn stabilizes the liquid-like micelle phase. In addition, the dehydration of core
region of the micelles due to increasing concentration or temperature leads to phase transition
3
from liquid-like to crystalline micelle state. These results can deepen the current understanding
of the complicated phase behaviors of amphiphilic copolymers.
Although the three systems studied have very different features, this work demonstrates that they
can all be tackled by similar SAS analysis. Furthermore, structure-property relationships and
structure-phase behavior relationships are established based on the results.
Thesis Supervisor: Sow-Hsin Chen
Title: Professor of Nuclear Science and Engineering
Thesis Reader: Sidney Yip
Title: Professor of Nuclear Science and Engineering
and Materials Science and Engineering
4
Acknowledgments
First, I thanks for the funding supported by U.S. Department of Energy (DOE) to Prof. Sow-Hsin
Chen. Because of it, I can finish my thesis work without worrying the financial resource. During
my six years at MIT, many people helped me to make this thesis possible. Among them, I specially
thank my thesis supervisor Professor Sow-Hsin Chen, who inspired me, guided me to the field of
neutron/X-ray scattering, and challenged me to think more deeply. His enthusiasm for science has
encouraged me and his deep physical insight has helped me to understand my research problems.
Also, I would like to express my sincere gratitude to my thesis reader Professor Sidney Yip, who
encouraged me and offered me invaluable advices on both my research and my career life. My
thanks also go to Professor Piero Baglioni and Dr. Emiliano Fratini, to whom I am truly indebted
for providing unconditionally experimental materials. I would also thank Professor Bilge Yildiz to
join my thesis committee and give me suggestions despite her very busy schedule.
I owe a great debt to my collaborators Prof. Piero Baglionil, Emiliano Fratini, U-Ser Jeng, Prof.
Sung-Min Choi, Yi-Qi Yeh, Chun-Jen Su, Sung-Hwan Lim, Giovanni Ferraro, Francesca Ridi,
Kao-Hsiang Liu, Christopher Bertrand, Yun Liu, Madhusudan Tyagi, William Heller, Ken Littrell,
Eugene Mamontov, Ahmet Alatas, Dazhi Liu, Zhe Wang, Hua Li, Jer-Lai Kuo, Mingda Li, Peisi
Le, Kanae Ito for their substantial assistance in sample preparations, experiments, and all other
possible ways. I specially thank Wei-Ren Chen and Xin Li for their discussion and suggestions.
My acknowledgment also goes to the countless others at MIT, NIST, ORNL, NSRRC, who have
helped me. All of your efforts made the work in this thesis possible.
During the years at MIT, I fortunately met a lot of friends, who have made my life more enjoyable
and fun. I would like to specially thank Kao-Hsiang Liu, Stephanie Lam, Heather Beem, Michelle
Chang, Nan Li, Yu Gao, Chia-Yu Chen, Chia-Hung Chen, Yue Fan, Xiangqiang Chu, Yang Zhang,
Marco Lagi, Dazhi Liu, Fei Yan, Nicolas Stauff, and Naveen Prabhat.
I really want to thank sisters and brothers in CBCGB who support me and pray for me all the time.
I want to give thanks to my God, Jesus Christ, who guides me and leads me through the whole
Ph.D. journey. Without Him, I couldn't go this far.
5
Finally, I dedicate this thesis to my father, Chien-Wen Chiang, my mother, Mei-Lien Chang, and
my brother, Wei-Lun Chiang. I love you.
6
Contents
List of Figures ...............................................................................................................................................
9
List of Tables .............................................................................................................................................. 14
Chapter 1.....................................................................................................................................................15
Introduction.................................................................................................................................................15
1.1 Disordered Colloidal Systems...........................................................................................................15
1.2 Small-Angle Scattering (SAS)..........................................................................................................15
1.3 Overview of the Thesis .....................................................................................................................
18
Chapter 2.....................................................................................................................................................20
M icrostructure of Calcium -Silicate-Hydrate Gel................................................................................... 20
2.1 Introduction.......................................................................................................................................20
2.1.1 M icrostructure of Pure Calcium -Silicate-Hydrate Gel........................................................... 20
2.1.2 Effect of Polycarboxylic Ether (PCE) A dditives ................................................................... 25
2.1.3 Effect of M ethylhydroxyethyl Cellulose (Culm inal)............................................................ 28
2.1.4 Effect of Ca/Si Ratio..................................................................................................................29
2.2 Materials ........................................................................................................................................... 30
2.2.1 Pure C-S-H gels w ith Different W ater Content ..................................................................... 30
2.2.2 C-S-H gels with Polycarboxylic Ether (PCE) A dditives ....................................................... 31
2.2.3 C-S-H gels with Methylhydroxyethyl Cellulose (Culminal) Additives.....................................32
2.2.4 C-S-H gels with Different Ca/Si Ratio ................................................................................... 32
2.3 Analytical Form of Small-Angle Scattering (SAS) Model............................................................... 33
2.4 Results and Discussion .....................................................................................................................
38
2.4.1 Pure C-S-H gels with Different Water Content ..................................................................... 38
2.4.2 Effect of Polycarboxylic Ether (PCE) Additives ................................................................... 48
2.4.3 C-S-H gels with Methylhydroxyethyl Cellulose (MEHC, Culminal) Additives ................... 59
2.4.4 C-S-H gels with Different Ca/Si Ratio................................................................................... 64
Chapter 3.....................................................................................................................................................69
Microstructure of Magnesium-Silicate-Hydrate Globules..........................................................................69
3.1 Introduction.......................................................................................................................................69
3.2 Materials ........................................................................................................................................... 70
3.3 Analytical Form of Small-Angle X-ray Scattering (SAS) Model................................................. 72
3.3.1 Inter-globule structure factor ................................................................................................
7
73
3.3.2 Intra-globule structure factor .................................................................................................. 73
3.4 Results and Discussion .....................................................................................................................
76
3.4.1 N anom eter to subm icron length-scale...................................................................................
76
3.4.2 Angstrom length-scale ...............................................................................................................
84
3.4.3 Submicron to m icrom eter length-scale ..................................................................................
86
Chapter 4.....................................................................................................................................................88
M icrostructure of Pluronics M icellar Solutions.....................................................................................
88
4.1 Introduction.......................................................................................................................................88
4.2 Materials ...........................................................................................................................................
90
4.3 Analytical Form of Sm all-Angle N eutron Scattering (SAN S)..........................................................91
4.3.1 Intraparticle Structure Factor ..................................................................................................... 92
4.3.1 Interparticle Structure Factor................................................................................................
95
4.4 Results and Discussion.....................................................................................................................96
4.4.1 Effect of Molecular Weight...........................................................................
98
4.4.2 Effect of Temperature..............................................................................................................103
4.4.3 Effect of Concentration............................................................................................................106
4.4.4 Effect of Hydrophobic/Hydrophilic (PO/EO) Ratio ................................................................
Chapter5.....
..............................
..................................................................... 115
Sum mary and Future Work.........................................................................................................................
5.1 Sum mary .......
110
.......................................................................................................................
115
115
5. 1.1 Cement binders........................................................................................................................
115
5.1.2 Pluronics M icellar Solutions ....................................................................................................
118
5.2 Future Work M i..... a..........
....................................................................................................
5.2.1 Cement binders ........................................................................................................................
121
121
5.2.2 Pluronics Micellar Solutions....................................................................................................123
Appendix A...............................................................................................................................................124
A List of Publications ...............................................................................................................................
124
Bibliography .............................................................................................................................................
127
8
List of Figures
Figure 2.1.1- 1 (a) Jennings' colloidal Model-II, CM-II. The C-S-H gel has a fractal structure with a fractal
dimension, D, and a cutoff length,
. (b) Structure of the basic building block of the C-S-H gel, i.e. the
globule. R is the disk radius, 0 is the angle between the wave vector
Q
and the rotation axis of the globule,
L, and L 2 are the layer thickness of hydration water and hydrated calcium silicate, respectively, and p,
and p2 are their corresponding scattering length densities (slds). p, is the solvent sld.
3
thickness of the globule.
.. ..
t is the total
....................................................................................................
22
Figure 2.1.2- 1 Chemical structure of the investigated polycarboxylic ethers (PCEs) with controlled density
(n:m) and length (p) of the side chains.34 .................................................. . . . .. . . . .. . . .. . . . .. . . .. . . .. . . . .. . . .. . . . .. . . . 27
Figure 2.1.3- 1 Chemical structure of methylhydroxyethyl cellulose (MHEC)...................................29
Figure 2.4.1- 1 Absolute intensity
I(Q)
versus
Q
for C-S-H at three different water contents: 10% (black
square), 17% (red circle), and 30% (blue triangle) at 25 C. The inset shows the enlargement of the peak
arising from the interlamellar distance of the globule. The error bars throughout the text represent one
stan dard deviation .3 ..................................................................................................................................... 39
Figure 2.4.1- 2 Model fitting results of C-S-H gel at water content (a) 10% (b) 17%. The upper left panel
shows the absolute intensity of the data (green circle) and its corresponding fitted curve (red line), the upper
right panel shows the effective Schultz distribution of the number of layers in the globules, the lower left
panel shows the structure factor S(Q) of the fractal structure, and the lower right panel shows the particle
structure factor of the globule (P(Q))orientatio,n . The error bars of the experimental data in upper left panels
represent one standard deviation and are smaller than the circle. The fitted parameters used here are listed
in Table 2.4.1- 1.3
..........
................................................................................................... 42
Figure 2.4.1- 3 Model fitting results of C-S-H gel at water content 30% at 25 *C. The upper left panel
shows the absolute intensity of the data (green circle) and its corresponding fitted curve (red line), the upper
right panel shows the effective Schultz distribution of the number of layers in the globules, the lower left
panel shows the structure factor S(Q) of the fractal structure, and the lower right panel shows the particle
structure factor of the globule (P(Q))rientatio,n . The error bars of the experimental data in upper left panels
represent one standard deviation and are smaller than the circle. The fitted parameters used here are listed
in Table 2.4.1- 1.3
..........
................................................................................................... 43
Figure 2.4.1- 4 Illustration of C-S-H globule microstructure at water content of 30%. The average number
of layers n = 10.9, the standard deviation odistance L = 11.3
= 10.2, the disk radius R = 95.0
A,
and the interlayer
A with water layer thickness L, = 7.9 A and calcium silicate layer thickness L 2 = 3.5 A.
9
The number of layers follows a Schultz distribution as shown in the upper right panel in Figure 2.4.1- 3.
The globules are indeed disk-like objects.3................................................ .. . . . .. . . . . . .. . . . .. . . . . . .. . . . .. . . . . .. . . . . . . 48
Figure 2.4.2- 1 Model fitting results of the pure C-S-H sample. (a) Experimental data of SAXS (blue open
circle) and SANS (black open circle) and the corresponding data fitting curves of SAXS (cyan line) and
SANS (red line) of the pure C-S-H sample. The SAXS experimental and fitting intensities are shift in yaxis by timing a factor 10 for clarity. (b) inter-particle structure factor S(Q) of the SAXS data (blue solid
triangle) and SANS data (black solid circle, not seen because it is almost the same curve as the s(Q) of the
SAXS data) and intra-particle structure factor P(Q) of the SAXS data (green open triangle) and SANS data
(red open circle) used to fit the data in panel (a). The difference in P(Q) comes from the different x of
neutron and X-ray. The error bars of the experimental data represent one standard deviation. The cartoons
in panel (a) show the fractal structure suggested by s(Q) and the multi-layered cylinder model we use for
P(Q) .4..........................................................................................................................................................
50
Figure 2.4.2- 2 Model fitting results of (a) SAXS data and (b) SANS data. Both panels show the
experimental data for pure C-S-H (black open square), C-S-H/PCE23-2 (blue open up-triangle), C-S-
H/PCE23-6 (magenta open left-triangle), C-S-H/PCE102-2 (navy open diamond), C-S-H/PCE102-6 (pink
open hexagon), and the data fitting curves for pure C-S-H (red), C-S-H/PCE23-2 (orange), C-S-H/PCE236 (cyan), C-S-H/PCE102-2 (green), C-S-H/PCE102-6 (dark yellow). The experimental and fitting
intensities are shifted in y-axis by timing factors of 104 (pure C-S-H), 103 (C-S-H/PCE23-2), 102 (C-SH/PCE102-6), and 101 (C-S-H/PCE102-2) for clarity. 4 ...................................... . .. . . . . .. . . . . .. . . . . .. . . . . .. . . . .. . . . 51
Figure 2.4.2- 3 The effective Schultz distribution of the total thickness t = n L of the globules for samples
of pure C-S-H (black line with solid square), C-S-H/PCE23-2 (red line with solid circle), C-S-H/PCE23-6
(green line with solid up-triangle), C-S-H/PCE102-2 (blue line with solid down-triangle), C-S-H/PCE 1026 (magenta line with solid left-triangle). The normalization condition is
J fs (t) dt = L
54
.4................
0
Figure 2.4.2- 4 Detail of the thermogravimetric measurements, presented as derivative weight loss vs.
temperature, of the four C-S-H samples synthesized in presence of additives. The pure C-S-H sample (not
shown here) gives a smooth baseline showing no features in the reported temperature range and in particular
at 380 and 400 C. 4 .................................................................................................................................... 56
Figure 2.4.2- 5 FE-SEM images of (a)-(b) C-S-H, (c)-(d) C-S-H/PCE102-2, (e)-(f) C-S-H/PCE102-6, (g)(h) C-S-H/PCE23-2, and (i)-(j) C-S-H/PCE23-6. Images on the left correspond to 25X magnification (bar
= 1 Pim) while images on the right correspond to 75X magnification (bar = 200 nm). 4 ............ . . . . . .. . . . .
. .
58
Figure 2.4.3- 1 Model fitting results of SAXS data for C-S-H (blue open circle) and C-S-H/MHEC (red
open up-triangle). The corresponding data fitting curves are denoted by black lines. The experimental and
fitting intensities for C-S-H are shifted in y-axis for clarity. The error bars of the experimental data represent
one standard deviation and are smaller than the symbols. The fitted parameters used here are listed in Table
2.4.3- 1.5
..................................................................................................................... 61
Figure 2.4.3- 2 The effective Schultz distribution of the total thickness t = nL of the multilayer disk-like
globules, due to the distribution of the number of repeating layers n, for C-S-H (blue solid square) and CS-H/MHEC (red solid circle). We assume no distribution of the disk radius R of the globules. The
fs (t) dt = 1.5....................................................................................................62
norm alization condition is
0
10
Figure 2.4.3- 3 SEM micrographs of: (a) C-S-H and (b) C-S-H/MHEC at magnification 90 kX. Scale bar
is 200 nm. . ................................................................................................................................................. 63
Figure 2.4.4- 1 Model fitting results of SAXS data for C-S-H with Ca/Si = 1.0 (blue open square) and CS-H with Ca/Si = 1.4 (red open diamond). The corresponding data fitting curves are denoted by black lines.
The experimental and fitting intensities for C-S-H with Ca/Si = 1.0 are shifted in y-axis for clarity. The
error bars of the experimental data represent one standard deviation and are smaller than the symbols. The
fitted parameters used here are listed in Table 2.4.4- 1.. ....................................................................... 66
Figure 2.4.4- 2 The effective Schultz distribution of the total thickness t = nL of the multilayer disk-like
globules, due to the distribution of the number of repeating layers n, for C-S-H with Ca/Si = 1.0 (blue solid
circle) and C-S-H with Ca/Si = 1.4 (red solid square). We assume no distribution of the disk radius R of the
globules. The normalization condition is Jfs (t) dt =1..
...........................
......
67
0
Figure 2.4.4- 3 SEM micrographs of: (a) C-S-H with Ca/Si
=
1.0 and (b) C-S-H with Ca/Si = 1.4 at
magnification 90 kX . Scale bar is 200 nm .5 .................................................
.. . . . .. . . . .. . . . .. . . . .. . . . .. . . .. . . .. . . .. . . . .
68
Figure 3.4.1- 1 The SAXS experimental data for MSH (violet open circle) and MSH* (pink open diamond).
The data fitting curves using C-S-H multilayer disk-like model are denoted by black lines. The experimental
and fitting intensities are shifted in y-axis by timing a factor of 10 for MSH for clarity. The error bars of
the experimental data represent one standard deviation and are smaller than the symbols. The fitted
param eters used here are listed in Table 3.4.1- 1................................................................................... 77
Figure 3.4.1- 2 Model fitting results of SAXS data for MSH (violet open circle) and MSH* (pink open
diamond), using polydisperse spheres as intra-particle structure factor. The data fitting curves are denoted
by black lines. The experimental and fitting intensities are shifted in y-axis for MSH for clarity. The error
bars of the experimental data represent one standard deviation and are smaller than the symbols. The fitted
param eters used here are listed in Table 3.4.1- 2.................................................................................. 80
Figure 3.4.1- 3 The Schultz distribution of the radius R of the spherical globules for MSH (violet solid
circle) and MSH* (pink solid diamond). The normalization condition is
Jfs (R)dR =1 ..................... 81
0
Figure 3.4.1- 4 Model fitting results of SAXS data for CSH (blue open diamond), MSH (red open circle),
and Mixed (olive open up-triangle), and the corresponding data fitting curves are all denoted by black lines.
The experimental and fitting intensities are shifted in y-axis for MSH and Mixed for clarity. The error bars
of the experimental data represent one standard deviation and are smaller than the symbols. The fitted
param eters used here are listed in Table 3.4.1- 2.. ................................................................................. 83
Figure 3.4.2- 1 WAXS data for CSH (blue), MSH (red), and Mixed (olive). "*" indicates the peaks
attributed to Tobermorite Cas(Si6O1 6(OH) 2).4(H20) 38 and "#" denotes the peaks contributed by Lizardite
(Mg 3Si 2Os(OH) 4). 74 The WAXS intensities are shifted along the y-axis for the sake of clarity.5
.. . . . . .
85
Figure 3.4.3- 1 SEM micrographs of: (a) CSH and (b) MSH (c) Mixed at magnification 90 kX. Scale bar
is 200 nm
.
. ....................................................................................................................
11
87
Figure 4.4.1- 1 The SANS experimental data and the corresponding model fitting curves for 0.05 g/ml
micellar solutions of (a) F88 and (b) F108 Pluronics copolymers at 60 0C in 100% D 20 (magenta open
right-triangle), 90% D 20 (olive open diamond), 80% D 20 (blue open up-triangle), and 70% D20 (red open
circle). The fitting curves are denoted by black lines. The error bars of the experimental data represent one
standard deviation and are smaller than the symbols. The experimental and fitting intensities are subtracted
by a constant incoherent background and shifted on the y-axis for the sake of clarity. (c) The neutron
scattering length density (SLD) profile of the F88 (dotted line) and F108 (solid line) micelles pmicee(r) with
the same colors as described in (a) and (b). The orange lines are SLD profile of polymeric component
ppoiymer(r). r represents the distance to the micelle center. (d) The radial water number density distribution
H(r) determined from equation (4.3.1.6) for F88 (red line) and F108 (blue line). The inset shows the
accumulated number of water distribution within the sphere with radius r..............................................102
Figure 4.4.1- 2 Illustration of microstructure change of type B Pluronics micellar solutions when increasing
molecular weight.......................................................................................................................................103
Figure 4.4.2- 1 The SANS experimental data and the corresponding model fitting curves for 0.05 g/ml
micellar solutions in 100% D 20 of (a) F88 and (b) F 108 Pluronics copolymers at temperature 80 "C (orange
down up-triangle), 70 C (magenta open right-triangle), 60 *C (olive open diamond), 50 0C (blue open uptriangle), and 40 C (red open circle). The fitting curves are denoted by black lines. The error bars of the
experimental data represent one standard deviation and are smaller than the symbols. The experimental and
fitting intensities are subtracted by a constant incoherent background and shifted on the y-axis for the sake
of clarity. The extracted water number density distribution H(r/Rmn) for (c) F88 and (d) F108. The inset is
the enlargement of H(r/Rin) within the micellar core. The colors shown in (c) are the same as described in
(a) and that in (d) are the same as described in (b) .................................................................................. 105
Figure 4.4.2- 2 Illustration of microstructure change of Pluronics micellar solutions when increasing
temperature...............................................................................................................................................106
Figure 4.4.3- 1 (a) The SANS experimental data and the corresponding model fitting curves for F108
micellar solutions in 100% D 20 at 80 *C with concentration of 0.18 g/ml (olive open diamond), 0.05 g/ml
(blue open up-triangle), and 0.01 g/ml (red open circle). The fitting curves are denoted by black lines. The
error bars of the experimental data represent one standard deviation and are smaller than the symbols. The
experimental and fitting intensities are subtracted by a constant incoherent background and shifted on the
y-axis for the sake of clarity. (b) Inter-particle structure factor S(Q). (c) The extracted water number density
distribution H(r/Rn). The inset is the enlargement of H(r/Rin) in shell region. (d) The extract polymeric SLD
distribution ppolymer(r). The colors shown in (c), (d) are the same as described in (b)...............................109
Figure 4.4.3- 2 Illustration of microstructure change of type B Pluronics micellar solutions when increasing
concentration of the copolymers...............................................................................................................110
Figure 4.4.4- 1 (a) The SANS experimental data and the corresponding model fitting curves for micellar
solutions in 100% D2 0 at 40 C for F108 0.05 g/ml (magenta open right-triangle), L64 0.05 g/ml (olive
open diamond), L64 0.01 g/ml (blue open up-triangle), and P84 0.01 g/ml (red open circle). The fitting
curves are denoted by black lines. The error bars of the experimental data represent one standard deviation
and are smaller than the symbols. The experimental and fitting intensities are subtracted by a constant
incoherent background and shifted on the y-axis for the sake of clarity. (b) The extracted water number
density distribution H(r/Rin). The colors shown in (b) is the same as described in (a).............................113
12
Figure 4.4.4- 2 Illustration of microstructure change of Pluronics micellar solutions when varying PO/EO
ratio (hydrophobicity/hydrophilicity character)........................................................................................114
Figure 5.1.1- 1 Summary of structure-property relationships of cement binders studied........................118
Figure 5.1.2- 1 Summary of structure-phase behavior relationships of micellar solutions studied.........121
13
List of Tables
Table 2.1.2- 1 Characteristics of the Polycarboxylate-type Superplasticizers 34
. . .. . .. . . .. . .. .. . .
27
Table 2.4.1- 1 Parameters extracted from the model fitting for samples measured at 25 C3 , a,b,f ........ 44
Table 2.4.2- 1 Parameters extracted from the model fitting of SAXS and SANS data 4,a...........................52
Table 2.4.3- 1 Parameters extracted from the model fitting of SAXS data of C-S-H and C-S-H/MHEC,a
.................................................................................................................................................................... 61
Table 2.4.4- 1 Parameters extracted from the model fitting of SAXS data of C-S-H with Ca/Si = 1.0 and
C-S-H with Ca/Si = 1.45,a .........................................................................................................
66
Table 3.2- 1 Chemical composition of the different silicate hydrates investigated. 5 .............. . . .. . . . .. . . . .
. .
72
Table 3.4.1- 1 Parameters extracted from the model fitting of SAXS data of M-S-H samples using C-S-H
multilayer disk-like modela ......................................................
77
Table 3.4.1- 2 Parameters extracted from the model fitting of SAXS data of CSH, MSH, MSH* and Mixed
samplessa
...................................................................
79
Table 4.2- 1 Properties of PEO-PPO-PEO Triblock Pluronics Copolymers Used in this Work ........... 91
Table 4.4- 1 Parameters Extracted from Global Model Fitting of SANS Data of PEO-PPO-PEO Triblock
Pluronics Copolym ers U sed in this W orka............................................................................................. 96
Table 4.4- 2 Parameters Related to Hydrationa
.........................................
97
14
Chapter 1
Introduction
1.1 Disordered Colloidal Systems
A colloid is a system where dispersed insoluble particles are disorderedly suspended
microscopically throughout another substance. Unlike a solution, in which solute and solvent form
only one phase, a colloid has a dispersed phase, i.e. the suspended particles, and a continuous phase,
i.e. the medium of suspension. To qualify as a colloidal system, the mixture should not settle or
would take a very long time to settle appreciably. The dispersed particles have a linear dimension
between 10-9 m (10 A) and 10-6 m (1 im). For particles with smaller size range (r<250 nm), an
ultramicroscope or an electron microscope is required to see the structure in real-space. Particles
with size larger than 250 nm are normally easily visible in an optical microscope. On the other
hand, small-angle neutron scattering (SANS) and small-angle X-ray scattering (SAXS) are shown
to be powerful tools to probe the microstructure and the interactions in the colloidal systems with
particle size between 1 nm to 100 nm. 2
1.2 Small-Angle Scattering (SAS)
Small-angle scattering (SAS) is the collective name for the techniques of small-angle neutron
(SANS), X-ray (SAXS) and light (LS) scattering. Radiation is elastically scattered by a sample in
15
these techniques. By analyzing the resulting scattering pattern, we can obtain information about
the size, shape, orientation, or polydispersity of some components of the sample and the
interactions between the particles constituting the sample. SAS is a well-developed scattering
technique to study colloidal systems such as biological system, micellar solutions, and cement gels,
etc.
The small-angle scattering measures the spacial differential cross-section per unit volume as
1
N
I(Q)=i(Xb
2
(1.2.1)
2)
where bl is the scattering length of lth atom and is independent of the wave vector Q. For a isotropic
one component system bi = b. Then
I(Q)
(1.2.2)
= -- b2S(Q)
V
In a two phase system, such as micellar solutions, the scattering objects, i.e., micelle particles, can
be distinguished in appropriate conditions from the continuous solvent. Let's assume that there are
total N atoms in the system, Np macromolecules in solutions, N atoms in each macromolecule,
and Ns atoms for solvent molecules. Then we can re-write equation (1.2.1) into:
16
I
-
I(Q)=/
Np N.
j=1 1=1
Np
1
N,
1
- b,)eQ*i0' +
j=1
b, eiQrJ;
(1.2.3)
j=1
2
N.
[b(bm
V
e"
j=1
N.
Z (bmjn
j=1 1=1
Sy
bs
'' +
bme
2
NS
' .- r
m
s-b,)e'Q('R)]eiQR
1=1
+ Eb,
e'Q"
j=1
where bmyi is the scattering length of lth atom in the jth macromolecule, bs the scattering length of
a solvent atom/molecule. Since the solvent molecule is typically very small compared to 27t/Q, it
can be treated as a uniform continuous media. Thus, the last term in the above equation
Zb, e'Q"
j=1
is just 6(Q), which contributes only at
Q = 0.
Therefore, this last term can be considered as zero
since SANS only measures the intensity at a finite
Q value.
If we can further assume that each
macromolecule in the solvent is the same, and it is spherically isotropic, a more useful expression
is written as
N
I(Q)
(bm
2
N
-b, )e'Q (''~RI)
=1
V p'
e(1.4
s
=1
'(1.2.4)
= NPP(Q) Sin,.(Q)
V
where
Nm
2
P(Q)= Z(bmj, - bs)eiQ-( I-R)
(1.2.5)
Z=1
17
N_
2
(1.2.6)
e1QR2
Sit ,.(Q)=
N ;=
P(Q) is called the intra-particle structure factor, or form factor. Sinter(Q) is called the inter-particle
structure factor. P(Q) is only determined by the structure of each individual macromolecule and
Sinter(Q) describes
the correlations between the centers of macromolecules. In the study of the inter-
colloidal correlation in solutions, people usually drop the subscript and use S(Q) as the interparticle structure factor.
In general, the fitting of I(Q) require the knowledge of both P(Q) and S(Q). P(Q) describes the
size, shape, polydispersity, etc., of scattering objects. In principle, for a simple liquid sample, S(Q)
can be calculated through the Orstein-Zernike (OZ) equation once the inter-particle potential is
known.
1.3 Overview of the Thesis
This thesis is consisted of five chapters. Chapter 1 is a general introduction of disordered colloidal
systems that I am interested in and the main method, i.e. small-angle scattering (SAS), I used to
tackle the systems.
In the main body, I discuss my investigations on the microstructure of three seemingly very
different systems: calcium-silicate-hydrate (C-S-H) gels (Chapter 2),3-5 magnesium-silicatehydrate (M-S-H) gels (Chapter 3),5 and Pluronics micellar solutions (Chapter 4). Due to their
common feature of basic building particles dispersing disorderedly in a continuous medium, I
demonstrate that they can be tackled similarly through small-angle scattering. Wide-angle X-ray
18
scattering (WAXS) and scanning electron microscope (SEM) were also used to support and
supplement the findings. In each of these chapters, relevant sample descriptions, SAS analysis
models, data analysis results and discussion are explained. Most of the contents are based on my
publications in the past siX years, listed in Appendix
In Chapter 5 gives the summary of the current .work and some perspective of future work.
19
Chapter 2
Microstructure
Hydrate Gel
of
Calcium-Silicate-
2.1 Introduction
2.1.1 Microstructure of Pure Calcium-Silicate-Hydrate Gel
Cement is a synthetic material of largest production in modern society. There is more than 11
billion metric tons of cement consumed every year all over the world. However, to manufacture
one ton of Portland cement clinker, approximately 0.8 tons of C02 is emitted into the air, which
contributes 5% - 7% of the total human-made C02 emissions. 6 The requirement of reducing cement
usage therefore motivates many studies on properties of cement for the sake of a more efficient
use of this material. Hydrated calcium silicate gel (CaO)x(SiO2)(H20)y or shortly C-S-H is the
main binding phase in the commercial cement pastes. Its presence is critical to the development of
strength and durability of a cement paste. Studies of the microstructure of C-S-H and its effect on
the cement properties are therefore essential to the optimized usage of C-S-H-based cements.
C-S-H is a gel-like material. Existing C-S-H structural models relay on two different theories. On
one side, Feldman and Sereda (FS) and others7 '8 considered the C-S-H gel network as formed by
irregular C-S-H interconnected layers with adsorbed and interlayered water molecules. On the
other side, Power and Brownyard (PB) and others 91' 0 supposed the existence of basic C-S-H units,
which generate the C-S-H gel structure as a colloid made of small bricks and its associate gel pores.
20
Subsequently, Jennings11-13 combined the FS and PB hypothesis and obtained a hybrid model able
to give an exhaustive interpretation of several experimental evidences such as those derived from
scattering measurements14
15
and sorption isotherms experiments." According to Jennings'
Colloidal Model-II (CM-II)," C-S-H gel present in a hydrated cement paste can be described
schematically as shown in Figure 2.1.1- 1(a). This gel is consisted of assemblies of hydrated
globules immersed in aqueous solvent or air depending on the equilibrium water content. In this
context, the globules are multi-lamellar objects with an average thickness of about 4.2 nm. Inside
the globules, water can be located in both the interlayer spaces and the very small cavities, called
intraglobular pores (IGP), with dimensions around 1 nm. These building blocks pack together to
form a porous structure with two main classes of pores: the small gel pores (SGP) with dimension
of 1-3 nm and large gel pores (LGP) with size in the range from 3 to 12 nm. Greater pores are
usually referred as capillary pores.
21
(a)
(b)
D
z
1L
L~
0*L
t
Figure 2.1.1- 1 (a) Jennings' colloidal Model-II, CM-II. The C-S-H gel has a fractal structure with a fractal dimension,
D, and a cutoff length, J. (b) Structure of the basic building block of the C-S-H gel, i.e. the globule. R is the disk
radius,
0 is the angle between the wave vector
Q
thickness of hydration water and hydrated calcium silicate, respectively, and
scattering length densities (slds).
L,
and the rotation axis of the globule,
PAis the solvent sld.
p, and p
2
and
L2 are the layer
are their corresponding
t is the total thickness of the globule.3
Microstructure information is essential to predict and understand the mechanical behavior of the
material at larger length-scales.'
6
In the cement field, several empirical relations were developed
to show that the compressive strength is a function of the cement microstructure, especially the
porosity. This is valid in general for other brittle materials."7 The advancement of statistical
nanoindentation technique allowed one to locate the high and low density C-S-H phases in cement
pastes prepared at water-to-cement ratios lower than 0.4. Moreover, it provided strong evidences
for the existence of a ultra-high density phase along with the well-known high and low density CS-H phases.' 8"19
22
Neutron scattering technique has been extensively used on cement pastes to investigate the
structure of the developing C-S-H gel14, 5 ,20 and to access the dynamics of the water confined in
the gel porosity.2 1-23 In particular, Allen and coworkers" used small-angle neutron scattering
(SANS) technique to study the developing gel structure during the hydration process in Ordinary
Portland Cement (OPC). Their results suggested that C-S-H gel is formed by discrete globules
with 5 nm diameter which further aggregate together to give a scale-invariant structure with
correlation lengths up to about 40 nm. Based on this scenario, their analytical model comprises an
inter-globule structure factor, S(Q), describing the fractal nature of clustering with a mass fractal
dimension D of about 2.6 and an intra-globule structure factor, P(Q), representing an "effective"
spherical shape with a diameter of about 5 nm. This picture turns out to be consistent with their
SANS and small-angle X-ray scattering (SAXS) results.14" 5 However, since they only explored
the Q-range up to about 0.2
Q was
A-1, where Q is the magnitude
of scattering wave vector, their highest
not enough to explore the details of the globule and therefore its internal structure is still
uncertain.
Very recently, Pellenq and coworkers 24 proposed a molecular model of C-S-H based on a bottomup atomistic simulation. Starting from a dry orthorhombic tobermorite lattice with a 11 A interlayer
spacing and using Grand Canonical Monte Carlo (GCMC) technique, they obtained a model in
which water is present both in the interlayer space and in the intralayer cavities inside the calcium
oxide layers. This model with calcium/silicon ratio (C/S) = 1.65 results in an interlayer spacing
ranging from 11.3 A to 11.9 A and C-S-H density of 2.56 g/cm 3 , a value close to the experimental
result of 2.6 g/cm 3 found by Allen et al.14 for a very similar C/S ratio = 1.7. Dolado et al.2 5,2 6
simulated the formation of C-S-H structures through the polymerization of Si(OH) 4 species which
were allowed to react in the presence of solvated calcium ions. This approach is very general and
23
is not based on any pre-imposed structural model. Their main results25 show that at low C/S ratios,
the simulated C-S-H systems resemble mixtures of 1.1, 1.4-nm tobermorite and jennite structures
with pentamers or longer chains, while at high C/S ratios, only short 1.4 nm tobermorite and jennite
pieces seem to be formed. Intermediate C/S ratios gradually evolve from long to short chains, and
from tobermorite- to jennite-like features. Notably, their recent MD simulations 2 6 suggest that CS-H gel forms a three-dimensional branched structure as a result of interweaving and restructuring
processes of growing C-S-H segmental branches (SB). Moreover, they showed that the scattering
and diffraction patterns calculated from SB structures are in good agreement with both SANS data,
measured by Allen et al.14 for
Q > 0.05 A-1,
which give evidence for a peak at
Q
and recent X-Ray Diffraction (XRD) investigations, 6
~ 0.5 A-1 linked to d-spacing in the calcium silicate layers of
about 12 A. Skinner et al.6 used XRD method to show that the synthetic C-S-H is nanocrystalline
with a characteristic nanograin size of about 3.5 nm and disclosed a remarkable resemblance of
synthetic C-S-H structure with 11
A tobermorite.
McDonald et al.2 ' analyzed NMR data of white
cement pastes considering water in both intra- and inter-C-S-H pores and proposed an alternative
microstructure of C-S-H gel without assuming a finite building block. They suggested that the CS-H intra-layer distance is about 15
A,
while the inter-C-S-H porosity is around 41 A thick.
Although all these studies indicate a characteristic intra-layer length-scale of 10-15
A, a direct link
between this length-scale and the globule proposed in CM-II is still missing.
In this study, we assume the globule to be a multi-lamellar object with unknown total thickness t
and radius R as depicted in Figure 2.1.1- 1(b). The globule has a layered sub-structure where
water and calcium silicate layers are alternatively repeated. The present approach is so general that
changing the two descriptive parameters t and R takes into account disks-like objects (t «2R),
spheroidal geometries ( t = 2R ) and even rod-like symmetries ( t
24
>> 2R
). In the following
discussion, we denote L as the inter-layer distance of the sub-structure. L can be decomposed into
one layer of water with thickness Li and one layer of calcium silicate with thickness L 2 and
therefore L = L, + L 2. The resultant unknown total thickness of the globule can then be calculated
as t = iL, where n is the average number of layers in one globule derived from our model fitting.
To the best of our knowledge, this model is the only one that can successfully describe the internal
structure of the globule itself and to justify SANS intensity distributions from low-Q region up to
1 ^-. Our model differs from the results of Dolado et al.2 6 and McDonald et al.27 , which do not
consider in an explicit way the existence of a primary building block for the C-S-H gel structure.
2.1.2 Effect of Polycarboxylic Ether (PCE) Additives
The mechanical properties of cement depend on the progressive maturation of hydrated porous
phases due to the continuous reaction of water with the cement. This hydration process can last for
several years. It is strongly affected by additives, many of which have been developed in recent
years. The efficiency of these additives to produce high-performance concretes (HPC), i.e. cement
with extremely low porosity and enhanced strength and elasticity, is continuously being
improved. 2 8,2 9,30 Superplasticizers (SPs) are compounds irreplaceable to the construction industry
that are used as additives to produce HPC. These polymers have been shown to improve the
flowability and workability of concrete pastes, to keep the water content of cement low, and to
ensure the high mechanical strength, shrinkage, and durability of the hardened cementitious
composite. 28 ,2 9 ,3 0 The comb-shaped polycarboxylic ethers (PCEs) are among the most effective
SPs used in the cement industry. The simplest PCEs are composed of a polyacrylic or
polymethacrylic anionic backbone with grafted polyethylene oxide (PEO) uncharged side chains.
25
Each of these pieces can be tuned to produce several graft copolymers varying in the molecular
weights and chemical structures. The effect of adding PCEs depends on the chosen chemical
3
structure, which can dramatically alter the interaction between PCEs and the cement matrix. 1-36
The adsorption of the PCEs on the surface of the cement particles increases if the density or length
of the PEO side chains is decreased. In particular, the decrease of side chain density increases the
number of negative charges (i.e. the number of free carboxylic groups on the backbone) while the
shortening of the PEO chain length reduces the overall steric hindrance, rendering the negative
charges on the backbone more accessible. It was therefore concluded by Zingg et al.3 7 that the
enhanced adsorption of the PCEs on cement particles is induced by the interaction of the carboxylic
groups on the PCE backbone with calcium ions and that different levels of adsorption modify the
rheology and hydration kinetics of the final cement pastes.
While the influence of PCEs on the macroscopic observables of cement (rheology, mechanical
properties, and hydration dynamics) has been reported in the literature,31-36 the change of the C-SH microstructure due to the PCE additives remains mostly unknown. In this study, we use the
combination of small-angle neutron scattering (SANS) and small-angle X-ray scattering (SAXS)
techniques to investigate the microstructural changes of the C-S-H (I) gel before and after the
addition of PCEs with defined chemical structures. Pure C-S-H gel together with four C-S-H gels
including different PCEs, namely, PCE23-2, PCE23-6, PCE102-2, and PCE102-6, were studied. 34
The details of chemical structures of these polymeric additives are listed in Table 2.1.2- 1 and
pictured in Figure 2.1.2- 1. To the best of our knowledge, this is the first time that the influence of
PCE additives on the microstructure of C-S-H gel has been studied in detail.
26
L
n
-m
NaO
0
0
H3C
P
Figure 2.1.2- 1 Chemical structure of the investigated polycarboxylic ethers (PCEs) with controlled density (n:m)
and length (p) of the side chains. 34
Table 2.1.2- 1 Characteristics of the Polycarboxylate-type Superplasticizers3 4
length of side
MNa
MWb
chain (p)
density of side
chains (n:m)
(g/mol)
(g/mol)
PDIC
PCE 102-2
102
2:1
16 800
78 000
4.7
PCE102-6
102
6:1
14 600
67 000
4.6
PCE23-2
23
2:1
8700
25 600
2.9
PCE23-6
23
6:1
7600
18 900
2.5
aMN: Number average molecular weight. bMw: Mass average
molecular weight. PDI = MW/MN: polydispersity index.
27
2.1.3 Effect of Methylhydroxyethyl Cellulose (Culminal)
The continuous extrusion of cement-based mixtures is a method to produce sheets, bricks, spacers,
sewer pipes, etc. It is one of the most promising applications to obtain new cementitious materials.
Compared with the production process of conventional ceramic materials, continuous extrusion
uses considerably little energy. Extrusion is a processing technique shown to impart high
performance characteristics to fiber-reinforced cementitious materials. 38 During the extrusion
process, a highly viscous and plasticlike mixture is forced to go through a die, which has a rigid
opening of desired cross section.
In order for the cement pastes to have extrusion process, an additive must be added to confer
fluidity and plasticity to the final paste and to enable it to be passed through the die, extruded, and
handled without changing in shape or cracking. One of the best-performing classes of polymers
used in extrusion process is methylhydroxyethyl cellulose (MHEC). Alesiani et al. 39 studied the
effect of MHEC on C 3 S by using NMR. Their results showed that the cellulosic additive interacts
with the water present inside the paste. Under these conditions, the hydration process becomes
more efficient as the water is gradually released from the cellulose ether to the calcium silicate.
In this study, we intend to investigate the MHEC effect on the microstructure of C-S-H gel. The
chemical structure of MHEC is sketched in Figure 2.1.3- 1.
28
CH 3
0U
OH
H2C
0
1OHO
\ OH
CH 3
O
O
I
HO.,C/CH2
H2
Figure 2.1.3- 1 Chemical structure of methylhydroxyethyl cellulose (MHEC).
2.1.4 Effect of Ca/Si Ratio
C-S-H is a nonstoichiometric compound. There are large local variations of Ca/Si molar ratio in
cement pastes, between 0.6 and 2.3 or greater. 40 4 2 For hydrated Portland cement pastes, the
average Ca/Si molar ratio of C-S-H is around 1.7. The Ca/Si ratio of C-S-H in hardened C3S or
neat Portland cement pastes is about 1.75 in avarage, 42 with a range of values within a given paste
from 1.2 to 2.1. If there is a supplementary cementing material in the paste, then the mean Ca/Si
value is further reduced, in some cases to less than 1.42 Dolado et al. 25,26 simulated the formation
of C-S-H structures through the polymerization of Si(OH) 4 species which were allowed to react in
the presence of solvated calcium ions. This approach is very general and is not based on any preimposed structural model. Their main results 25 show that at low C/S ratios, the simulated C-S-H
systems resemble mixtures of 1.1, 1.4-nm tobermorite and jennite structures with pentamers or
longer chains, while at high C/S ratios, only short 1.4 nm tobermorite and jennite pieces seem to
29
be formed. Intermediate C/S ratios gradually evolve from long to short chains, and from
tobermorite- to jennite-like features.
In this study, we intend to investigate the effect of Ca/Si ratio on the microstructure of C-S-H gel.
2.2 Materials
2.2.1 Pure C-S-H gels with Different Water Content
Synthetic C-S-H was prepared by hydrating pure C 3 S in an excess of water. A chemically pure
batch of tricalcium silicate was obtained from CTG-Italcementi (Bergamo, Italy) as a gift. The
specific surface area detected by N2 sorption isotherms (BET) and mean radius of the C3S used in
the present study resulted in 0.65 m2/g and 4.66 pm, respectively. Several C-S-H batches were
prepared by mixing 4 g of C 3S with 1150 g of distilled water. The water was previously boiled and
kept sealed to avoid any subsequent carbonation, taking place during the C 3S hydration reaction.
The excess of water in respect of C3S was essential to prevent any portlandite (Ca(OH)2) coprecipitation, without altering the C-S-H formation. The resulting C3S/water dispersions were
sealed in plastic bottles to avoid carbonation and continuously stirred for at least 40 days. The
synthesis was conducted at room temperature (i.e. 25 "C). This synthetic route is known to
minimize the Ca(OH)2 content while forming quite polydisperse C-S-H phase, which is usually
refereed as C-S-H (I).43 The dispersion was filtered under a N2 atmosphere to avoid carbonation
and the obtained solid was dried in an oven at 60 *C for three hours. The resulting C-S-H gel was
dried to the desired water content using a vacuum oven operating at temperatures below 100 C.
This maximum working temperature allows water to evaporate without causing structural damages.
Energy-dispersive X-ray spectroscopy (EDX) evidenced an average Ca/Si ratio of 1.5 with a
30
standard deviation of about 0.3 confirming the expected inhomogeneity of the sample. EDX
spectra were recorded using a X-sight Oxford-Cambridge microprobe coupled with a SEM
microscope. Thermo Gravimetric Analysis was performed both to determine the effective
hydration of the so-prepared C-S-H gels and to confirm a low carbonation level. Final water
content was obtained considering the weight lost up to 200 C and was normalized only to the
amount of C-S-H present in the sample, while Ca(OH) 2 and CaCO3 contributes were calculated
according to the literature 44 and subtracted out from the original weight of the sample. The
percentages of Ca(OH)2 and CaCO3 were always in the range 5-10% in respect of the total mass
of the samples. Thermogravimetric experiments were carried out with a SDT Q600 apparatus (TA
Instruments) heating the sample at 10 C/min from 25 C to 1000 C under a constant flux of pure
N2 (100 mL/min). 10%, 17% and 30% water content cases were achieved at the end of the drying
process.
2.2.2 C-S-H gels with Polycarboxylic Ether (PCE) Additives
Synthetic C-S-H was prepared by hydrating 4 g of pure tricalcium silicate (C3S) in 1150 g of: pure
water or 0.14 % w/w PCE aqueous solution (i.e. 0.4 g of polymer per 100g of dry C3S). The
chemically pure batch of C 3 S (CTG-Italcementi, Bergamo) had a specific surface area of 0.65 m 2/g
(BET). The molecular formulae of the four PCEs used in this study (i.e. PCE23-2, PCE23-6,
PCE102-2, PCE102-6) are reported elsewhere along with relative polydispersities. 34 PCE23-2 and
PCE23-6 have PEO side-chains, which are five times shorter than PCE102-2 and PCE102-6, while
series 6 (i.e. PCE23-6 and PCE102-6) has more free carboxylic groups on the backbone. As a
result, the adsorption ability results: PCE102-2 <PCE102-6 < PCE23-2 < PCE23-6. The hydration
reaction was conducted at 25 C for 40 days. The dispersions were filtered and the water content
31
was standardized by dehydrating the samples at 60 0C in a N2 atmosphere. Final water content was
about 20% as determined by thermogravimetric analysis on the so obtained solids. The sum of
Ca(OH)2 and CaCO3 contents was always lower than 5% in all cases. Further specific details on
the synthesis can be found elsewhere. 3 The details of chemical structures of these polymeric
additives are listed in Table 2.1.2- 1 and pictured in Figure 2.1.2- 1.
2.2.3 C-S-H gels with Methylhydroxyethyl Cellulose (Culminal)
Additives
Stock solutions of sodium metasilicate (Na2SiO3-4H20) and calcium nitrate (Ca(NO3)2-6H2O)
were prepared. The solutions with volume of 1:1 Ca:Si ratio were cooled to about 00 C and mixed
by stirring in a two-necked round-bottomed flask. Methylhydroxyethyl cellulose (commercial
name Culminal) was added as additive (2.4% w/w respect to the amount of tricalcium silicate).
The flask was kept in an ice-water bath under continuous N2 flux. The sodium silicate solution
was added first, followed by slow addition of the magnesium solution. The product was warmed
to ambient temperature and the precipitate settled readily, leaving a clear supernatant solution. In
order to remove residual sodium, the precipitate was washed (diafiltrated) with deionized water
under a N2 atmosphere (to avoid carbonation).
2.2.4 C-S-H gels with Different Ca/Si Ratio
Pure C-S-H gel was prepared through a double-decomposition synthesis according to the method.
Stock solutions of sodium metasilicate (Na2SiO3-4H2O) and calcium nitrate (Ca(NO3)2-6H2O)
32
were prepared. The solutions with volume of 1:1 Ca:Si ratio and 1.4:1 Ca:Si ratio were cooled to
about 0*C and mixed by stirring in a two-necked round-bottomed flask in order to prepare C-S-H
gels with Ca/Si ratio of 1 (sample C-S-H) and 1.4 (sample CSH-B). The flask was kept in an icewater bath under continuous N 2 flux. The sodium silicate solution was added first, followed by
slow addition of the magnesium solution. The product was warmed to ambient temperature and
the precipitate settled readily, leaving a clear supernatant solution. In order to remove residual
sodium, the precipitate was washed (diafiltrated) with deionized water under a N2 atmosphere (to
avoid carbonation). At the end of the process, a small fraction of the supernatant was analyzed for
Na* concentration using flame atomic absorption spectroscopy ([Na'] <0.20
0.01 ppm) to ensure
that the by-product NaNO3 was completely removed by the washing procedure.
2.3 Analytical Form of Small-Angle Scattering (SAS) Model
The C-S-H gel can be pictured as shown in Figure 2.1.1- 1(a). The gel is consisted of globules
packing into a fractal-like object, which is immersed in an aqueous solution or air depending on
the water content. The self-similar fractal structure with a fractal dimension D only extends to a
maximum cutoff dimension of . Denoting the number density of the globule in the C-S-H gel as
N,
and the equivalent spherical radius of the globule as Re, the effective pair correlation function
of the fractal structure can be written
1
4rrN, ReD
rD-3
(2.3.7)
exp
)
g(r)= D
as45,46,47
Therefore, we can derive the inter-globule structure factor of the porous C-S-H gel as
33
zr
sin(Qr) g(r)
S(Q) =1+NNpddr 4rr2
Qr
U
1
D 7(D -1) sin (D -1)tan' (Q )
[i + (g )- 2 (D-1)/2
(QRe)D
=1+
2.3.8)
sin (D -1) tan-1(Q
)
+
Re
45,46,47
(D -1)1
+ (Q
)2
(D-
)/
2
In equation (2.3.2), F(x) is the gamma function. The value of S(Q) at
limS(Q)=1+F(D+1)(
Q=
0 limit is given by
/ Re)D , which becomes Q-independent and flat with the magnitude
proportional to the D-th power of s/Re. This low-Q limit can be used to determine the magnitude
of . For the works done for pure C-S-H at different water content and C-S-H in the present of
PCE additive, the value of
was set to be 670
A
as obtained by Allen et al. 14 determined from
their low-Q data. For other cases, the parameter of was treated as a fitting parameter because we
had access to the even lower
Q data.
The model for the internal structure of the globule having layered sub-structure is depicted in
Figure 2.1.1- 1(b). Although Jennings' model doesn't assign a specific shape to the globules, SANS
data was analyzed by assuming a general form factor for the basic units constituting the gel, where
the aspect ratio can vary from cylinders to disks passing through spheroidal objects. In Figure
2.1.1- 1(b), R is the disk radius, 9 is the angle between the wave vector
Q
and the globule rotation
axis, L1 and L2 are layer thickness of hydration water and hydrated calcium silicate, respectively,
andpi and p2 are their corresponding scattering length densities (slds). ps is the solvent sld. Finally,
n represents the number of repeating layers inside a globule. The interlayer distance, L, is equal to
the water layer thickness, Li, plus the calcium silicate thickness, L2, i.e. L = LI + L2. It is important
34
to note that different combinations of R, L and n can change the overall aspect ratio of the globule
from a cylinder-like to disk-like object. In this regard, the presented model of particle structure
factor includes both of these cases naturally.
We define the normalized particle form factor as F(Q, pu)
-
_1
r
VP
PVP
p = cosO and
V
p(F) exp(iQ " F)d3r , where
is the volume of the globule. The newly derived normalized particle structure
factor P(Q, p) is given by
2J(QR
P(Q, P) = F(Q, p)2
1-
p2)
C2(A2 +B2),3-5
(2.3.9)
QR 1- p2
where
sin QuLI
B
Q
2
Q+Ln
sn
- L2) Bi
sinQp(nL
Qp
2
2
n[ L1 +L 2
2
2
+
Qp(nL-L 2 )
+
A=Xco
sin QpL2
co Qp(nL + L1 )
2
sin QpL2
.si Qpu(nL + L,) sn2
2
(2.3.10)
Qp
(2.3.11)
Qpu
2
2
ji QpL
(2.3.12)
2
=
Pl - Ps
- PS
(2.3.13)
pA -Ps
The particle structure factor P(Q, p) of the object shown in Figure 2.1.1- 1(b) must then be
averaged over all possible directions of globule axis relative to the scattering vector Q , i.e.
35
= JP(Q,p) dp. It can be shown that the derived particle structure factor satisfies
(P(Q))
\
Orientation
0
1 at
the normalization condition (P(Q, u))rea
Q = 0.
The number of layers n, the cylindrical globule radius R, and the interlamellar distance L should
in general have their own distributions. These will further smooth the function
(P(Q).
Here we only introduce an "effective" distribution for the number of layers to take into account all
the possible distributions of n, R, and L. It is straightforward to show that a polydispersity on L has
similar effect with the one on n. In this regard, the polydispersity on n is defined to be effective
because if polydispersities are present even on R and L these will be included in that of n. We
assume the effective polydispersity as a Schultz distribution
fs(n)= Z+1
n
)n)_
nZexp -
Z+1 n /F(Z+1)
(2.3.14)
Z>-1
where n is the mean of the distribution, Z is a width parameter, and F(x) is the gamma function.
2) 1 / 2
The standard deviation of the distribution can be calculated by an = (n2 -
= n /(Z + 1)V/2.
Therefore, the orientationally averaged globule particle structure factor is then further averaged
over the effective number of layer distribution, i.e., (P(Q))rientati,,n
-
f (P(Q))rIenttin f, (n) dn
0
As a result, the measured SAS intensity distribution in the unit of cm-1 can be expressed as:
I(Q) = Np {nrR2 [(P, - Ps)L + (p - Ps )L2 ]1 2(P(Q))
Orientatinn
2
36
S(Q)+ bg[l / cm]
(2.3.15)
From the discussion above, in principle we have unknown fitting parameters in the final form of
SAS intensity distribution listed as: an overall pre-factor which accounts for the number density
of the scattering objects; six parameters contained in (P(Q))rientatio,n: inter-lamellar distance L,
calcium silicate layer thickness L2, average number of layers ni in the globule, the width parameter
Z of Schultz distribution, sld contrast ratio parameter X = (p1 - Ps) /(P 2 - Ps), disk radius of the
globule R; two additional parameters coming from S(Q): the cutoff length
and the fractal
dimension D. For SANS measurement, a flat background bg due to the incoherent scattering of
hydrogen atoms in the sample is also added. The equivalent radius Re can be calculated as
Re = (3nR 2L/4)("3 1.
The combination of SANS and SAXS data analysis allows us to extract all the structural
in equation (2.3.9) should be further convoluted to the
I(Q)Measure =
I(Q) ®
Q
resolution function R(Q) , i.e.
,
parameters much more accurately by introducing additional fitting conditions. For SANS, I(Q)
R(Q) while for SAXS, dQ/Q is very small (< 0.02 ) so for the first
approximation, we neglect the
Q resolution effect
in the X-ray case. For the work of pure C-S-H
gels at different water content, we conducted SANS experiment only to do data analysis. For the
work of C-S-H with PCE additives, we used the combined SANS and SAXS measurements to
extract all the structural parameters. We concluded from this work that SAXS itself only can get
good enough results. Therefore, for other cases (C-S-H gels at different Ca/Si ratio and C-S-H gel
with Culminal additive), only SAXS experiments were carried out to investigate the microstructure
of the C-S-H gels.
37
2.4 Results and Discussion
2.4.1 Pure C-S-H gels with Different Water Content
Our goal in this work is to determine the effect of the equilibrium water content (WC) on the
geometrical parameters (interlayer distance L, average number of layers n , and radius R of the
basic unit, i.e. globule) of the C-S-H gel with good accuracy using formula derived in section 2.3.
While reducing the water content, the gel passes from a situation where the small gel pores are
partially filled (30%) to a situation where only one monolayer of water is present on the C-S-H gel
(10%).
Figure 2.4.1- 1 shows the absolute intensity of C-S-H with three distinct water contents of 10%,
17%, and 30% at 25 C. The low-Q region in all the three cases is a straight line when plotted in
log-log scale, suggesting that the globules pack together to form a fractal object. At high-Q region,
there is a diffraction peak associated with the interlayer distance within the globule itself. The inset
in Figure 2.4.1- 1 displays an enlargement of SANS curves in the peak region. It is clear that on
increasing the water content, the high-Q peak shifts to a lower
Q position,
which corresponds to a
larger interlayer distance. The peak width at water contents of 10% and 17% is much broader and
less defined than the 30% case. This suggests fewer repeating units (i.e. smaller n ) for lower WC
cases. The flat incoherent background level reflects the total amount of water confined in the C-SH gel.
38
102
0.05
%
I
0.08
0.00.04
101
5
-.
0
0.4
100
10-1
0.5
0.55
0.6
0.65
0.7
0.75
0.
25 0 C
-
-2
0.45
-A-
10%
17%
30%
10
I0'
10-2
100
Q-A1
I(Q)
Figure 2.4.1- 1 Absolute intensity
versus Q for C-S-H at three different water contents: 10% (black square),
17% (red circle), and 30% (blue triangle) at 25 C. The inset shows the enlargement of the peak arising from the
interlamellar distance of the globule. The error bars throughout the text represent one standard deviation.3
Figure 2.4.1- 2 shows the fitting results of C-S-H samples at water content of (a) 10%, (b) 17%,
and Figure 2.4.1- 3 shows that of 30%, all measured at 25 C. Our model agrees with the data over
the entire Q-range from 0.02 A' to 1.00 A-1 (see the upper left panel in Figure 2.4.1- 2 and Figure
2.4.1- 3). The fitted parameters for all the investigated samples are listed in Table 2.4.1- 1. When
conducting the fitting process, the parameter
fixed to
was taken from result of Allen et al.14 and kept
= 670 A. This approximation is reasonable for two reasons. Firstly, the
covered in the present experiment is not small enough (i.e. lowest
39
Q measured
Q
range we
is only 0.01
A-1)
to
allow us for a precise estimation of . Secondly, slightly changing
during the fitting process does
not affect the fitting results of other parameters significantly. An ultra SANS experiment is
required to unambiguously determine
. Re in our S(Q) is not a fitting parameter but is
mathematically calculated by Re = (3nR2L / 4)1 , taking into account the parameters extracted
from the globule geometry. For pure C-S-H gel with 10% and 17 % water content, the small gel
pores (SGPs) are empty so that p, should be close to the air sld while for 30% hydrated C-S-H
gel, the SGPs are almost filled by water so p, should be close to the bulk water sld. We therefore
use two different fitting sld contrast ratios X = (p1 - Ps) (p 2
-
Ps), one for 10% and 17% cases
and the other for 30% case, during the fitting process. To reduce the fitting parameters, we assume
here that the globule has the same radius R and the hydrated calcium silicate layer has the same
thickness L 2 for all the three investigated C-S-H gels. The interlayer distance, L , therefore only
changes with the water layer thickness, L. The assumption is reasonable since the C-S-H gels are
prepared by drying the same product into different water contents and the calcium silicate
dimensions (R and L2 ) should be fixed while only water contents can be changed.
Our results show that as the water content passes from 10% to 30%, the interlayer distance
increases as clearly shown by the shift of the peak positions in the inset of Figure 2.4.1- 1.
Interestingly, Yu and Kirkpatrick 4 8 showed by thermal analysis and XRD experiments that upon
heating, water could be lost by tobermorite in steps that corresponded to decreases in layer spacing
from 14 to 12, 11 and 9.6
A.
Only two of these cases can be compared with the present results (L
9 A for 10% and 17% and L ~ 11 A for 30%). It is worth to note that an interlayer spacing of
12 A is a value typical of the basal spacing for semi-crystalline C-S-H often observed in many
synthetic C-S-H preparations 6 and in particular when C-S-H (I) is the prominent phase. 49 Our
40
globally fitted calcium silicate thickness L 2 is 3.5 A, which is close to GCMC simulation results
as reported by Pellenq et al.2 4 ,50 Their molecular model was shown to be mechanically stable
during the course of long molecular dynamics (MD) simulations performed by Youssef et al., o
where the calcium silicate layer thickness resulted in the range 3.3-3.9 A. 2 4 ,50 With L 2 being 3.5
A, the
associated water thickness can be calculated by L, = L - L2 , and results in 5.5 A, 5.8
A for
10%, 17%, 30% cases, respectively.
41
A, 7.9
(a)
Schultz Distribution at <n>=4.53 Z=3.27 on,=2.19
T=250C HydationLevel=0.10
102
F-
(Q) (data fitting)
0.2
0.15
10
0.1
c
0.05
10- [1
102
0
5
1
10
n
0
15
2(
)
Q(A
0
10
107'
-
10
|--S(Q)
10
vs 0
(Q)vs0
--
10 2
10[
1002
10.-
10
1000
10
.2
10'
10
Q(A 1
)
)
0
Schultz Distribution at <n>=4.73 Z=3.95
0.25
T=25 C HydratonLeve=.1 7
.
102.
on=2.13
KO (
)
b)
10
10'
102
Q(A'
0.2
0.15
10
c
0.1
0.05
102 1
102
U-
10'
1
0
i0
5
10
15
20
)
Q(A-
10
-
s(Q) vs
Q
-
P(Q) vs
Q
3-
10
10.
0 10020a
10,'
10
.2
101
10e
10.'
Q(A 1)
io'
i0
10
Q(A 1
)
10
.
1000
Figure 2.4.1- 2 Model fitting results of C-S-H gel at water content (a) 10% (b) 17%. The upper left panel shows the
absolute intensity of the data (green circle) and its corresponding fitted curve (red line), the upper right panel shows
the effective Schultz distribution of the number of layers in the globules, the lower left panel shows the structure factor
S(Q) of the fractal structure, and the lower right panel shows the particle structure factor of the globule
P(Q) Orientation,n . The
error bars of the experimental data in upper left panels represent one standard deviation and
are smaller than the circle. The fitted parameters used here are listed in Table 2.4.1-
42
1.3
Schtz Dstribtdlon at <>=10.86 =0.14 o=10.16
0.08.
T=25 C HydratlonLevI=0.30
10,
I
0.06
10e
C0.04}
'0.02
(Q) xPmQt
10.2
0
1i
P
0
10
20
n
30
40
10
10
-P(Q)
2
02101
102
i
0(A1
i0d"
)
0
vs 0
10,
1000
1
10'
.2
104
10
O(A')
m
-'I
Figure 2.4.1- 3 Model fitting results of C-S-H gel at water content 30% at 25 C. The upper left panel shows the
absolute intensity of the data (green circle) and its corresponding fitted curve (red line), the upper right panel shows
the effective Schultz distribution of the number of layers in the globules, the lower left panel shows the structure factor
S(Q) of the fractal structure, and the lower right panel shows the particle structure factor of the globule
(K
rientation,n . The error bars of the experimental data in upper left panels represent one standard deviation and
are smaller than the circle. The fitted parameters used here are listed in Table 2.4.1-
43
1.3
I
3
Table 2.4.1- 1 Parameters extracted from the model fitting for samples measured at 25 C , a,bf
water
content
interlayer
distance
water layer
thickness
fractal
dimension
average
number of
standard
deviation
equivalent
globule
L (A)
L, ()c
D
layers
and
radius
n
Re (A)e
10%
8.98(1)
5.51(4)
2.75(1)
4.53(2)
2.2
65.7(1)
17%
9.29(1)
5.82(4)
2.69(1)
4.73(2)
2.1
67.4(1)
30%
11.33(1)
7.86(4)
2.58(1)
10.86(3)
10.2
95.0(7)
is fixed as 670 A.' 4
b Scattering length density (sld) contrast ratio x = (p,
a During the fitting process,
-
ps )/(p 2 - Ps) is fitted as -0.170 0.004 for 10% and 17%
hydrated C-S-H gel, assuming the small gel pores (SGPs) are filled by air and as -0.043 0.003 for 30% hydrated CS-H gel, assuming the SGPs are filled by water.
L, is calculated byIL = L - L, where calcium silicate thickness L2 is globally fitted as 3.47 0.04 A.
d
is calcuat bn
by a,,=(n -h
2
)I
2
Z is an individually fitted width parameter of Schultz
=i(Z 1)1/2, where
distribution.
e R, is calculated by Re =
(3nR2L/41 , where disk radius R is globally fitted as 96.3 +0.1 A.
fThe error bars shown in the table is one standard deviation from the non-linear least square fitting process.
The interlayer distance L and the average number of layers n in 10% and 17% cases do not
change too much. However, when increasing the water content from 17% to 30%, the globule
geometrical parameters L,
W, and a,
(standard deviation of the number of layers) all increase
significantly and the corresponding "equivalent" radius, Re, increases from 67 A to 95
A.
for the low water content cases of 10 % and 17%, the equivalent globule radius (about 65
A)
more than twice of the sphere radius (about 25
Even
A)
is
given by Allen et al.,'5 where their SANS
analysis was simply based on a spherical form factor of the C-S-H globule. The total thickness of
the basic unit (t = nL) results in 40.7
A, 43.9 A,
123.0
A for
10%, 17%, 30% cases, respectively.
(
The 10% and 17% samples have globule thickness t close to what was expected in the CM-II
42
A) 1
while 30% case has t far from 42
A.
However, considering more closely the fs (n)
distribution shown in the upper right panel of Figure 2.4.1- 3, we find that its maximum is located
44
at n ~ 2. This clearly indicates that 30% hydrated C-S-H gel is dominated by globules with
thickness nL - 22.7
A.
Our fitting results also show that decreasing the water content from 30% to 10% will cause an
increase in the mass fractal dimension D from 2.58 to 2.75. Therefore, low WC C-S-H gel
presents less open structure than high WC C-S-H gel as a result of the shrinking imposed by the
de-hydration process. Similar values of D were reported by Allen et al.14 in 28-days cured cements
and also by some of the authors of the present paper even in younger C 3S pastes. 20
Based on our fitting results, the microstructure of the 30 % case can be described as in Figure
2.4.1- 4. C-S-H globules are indeed disk-like objects made up of repeating lamellae with thickness
of about 11 A. The lamellar structure is composed of water layer with thickness of 7.9
A
and
calcium silicate layer with thickness of 3.5 A. The lamellar "face" has a dimension of 2R = 190 A.
The globules have an effective size dispersion described by the Schultz distribution shown in the
upper right panel in Figure 2.4.1- 3. When decreasing the water content from 30% to 17%,
interlayer distance of the globules becomes smaller (see Table 2.4.1- 1) because of the decrease of
the water layer thickness. Using the globally fitted calcium silicate thickness for all three cases
(3.5 A), the water layer thickness decreases significantly from 7.9 A for 30% case to 5.8
A
for
17% case. In addition, the average number of layers of the globule n and its standard deviation
6,
decrease substantially when changing from 30% to 17% case. This suggests that during drying,
the globules tend to decompose or agglomerate (corresponding to those highly populated small
n ~ 2 globules in 30% case, see upper right panel of Figure 2.4.1- 3) themselves into a more
uniform size from the initially prepared higher WC gel, which has large size dispersion. The more
uniform size of the globules in low water contents, i.e. 10% and 17%, enables the globules to pack
into a more compact structure, indicated by their larger fractal dimensions (D = 2.75 for 10% and
45
D = 2.69 for 17%) compared with the 30% case (D =2.58). Further drying from 17% to 10% would
not change too much the shape parameters of globules since the size becomes rather uniform at
low WC.
Although the globular sizes obtained here differ from what found in other references, 4" 5 it should
be pointed out that the globule morphologies are very likely depending on the ways of preparing
samples. In this regard, we decided to prepare C-S-H gel using a high w/c ratio to minimize and
possibly avoid Portlandite formation, whose presence could result in a misleading interpretation
of the SANS curves. In addition, as far as we know, this is the first time in the literature that
synthetic C-S-H (I) instead of C-S-H embedded in cement is studied by SANS. Therefore,
variations could be expected. The proposed approach provides a direct way, other than indirect
methods such as N2 sorption isotherms1 ' and NMR 27, to evaluate the C-S-H globule geometrical
,
parameters. To the best of our knowledge this is also the first time that so many parameters L , L 2
R, n , and o- of the C-S-H globule have been obtained from SANS data analysis.
It is of fundamental importance to stress that the present results do not preclude the possibility for
the real C-S-H to be a continuous extension of branched and interconnected multilamellar sheets
where the basic units would be the smallest inhomogeneity (with a disk-like symmetry) present in
the sample and the fractal dimension along with the correlation length would describe how these
inhomogeneities are arranged in the volume. This assessment would reconcile the present model
(and consequently the CM-II) with what has been recently proposed by McDonald et al. 27 and
Dolado et al. 2 5,26 without decreasing the importance of the present approach which actually allows
us to disclose in a direct way the intra-layer spacing, inhomogeneity dimension, and related
polydispersity and moreover to characterize how these entities and the overall C-S-H fractal
structure would respond to different environmental stimuli (hydration degree, temperature,
46
concentration of additive, etc.). Dolado et al. 26 have demonstrated that the simulated SANS curve
corresponding to their branched structure also shows a mass fractal regime in low-Q part and their
simulated XRD result shows a well-defined peak at 0.55 A-1 corresponding to a d-spacing of about
12 A. These features are both present in our extended Q-range SANS curves and therefore we don't
exclude a three-dimensional branched structure. In addition, their MD simulation results 26 indicate
Segmental Branches (SB) with size of 30*30*60 A 3 while our results indicate a larger building
block with averaged size of about 200 (diameter)*200 (diameter)*40 (total thickness) A 3 for 10%
and 17% cases and of 200*200*120
A3 for
30% sample. Our much larger sized building blocks
suggest that a more continuous C-S-H structure with planar pores as proposed by McDonald et
al.27 can also explains the whole picture. However, we chose the Jennings' description to model
our SANS intensity distributions due to its "feasibility" to write down an analytical form factor
where we could explicitly include the interlayer spacing.
Calcium silicate layer is assumed to have the same thickness L 2 for all the investigated samples.
Further experiments such as contrast variation by SANS and SAXS measurements are necessary
to highlight possible changes of L2 with water content and to confirm this assumption. In addition,
by extending the measurement down to 0.001
k-1,
where P(Q) approaches to unity (see lower-
parameter
.
right panel in Figure 2.4.1- 2 and Figure 2.4.1- 3), we should be able to accurately determine the
47
Calcium Silicate
Sheets
0
Interlayer Space
with PhysicalIN
Bound H2 0
Liquid H 20
in
Nanopores
%oo
Figure 2.4.1- 4 Illustration of C-S-H globule microstructure at water content of 30%. The average number of layers
n = 10.9, the standard deviation 6- = 10.2, the disk radius R = 95.0 A, and the interlayer distance L = 11.3 A with
L, = 7.9 A and calcium silicate layer thickness L2 = 3.5 A. The number of layers follows a
Schultz distribution as shown in the upper right panel in Figure 2.4.1- 3. The globules are indeed disk-like objects. 3
water layer thickness
2.4.2 Effect of Polycarboxylic Ether (PCE) Additives
We first conducted non-linear least square fitting to SAXS data and used the resulting parameters
as known parameters to input into the SANS model, allowing only NSANS,
XSANS
and bgsANS to
change. We found Dsxs and DSANS separately by fitting the SAXS and SANS data in the range of
0.0065 A
<
Q
< 0.009 ^- with I = c * Q-D . In this region, 1/
structure factor is proportional to Q-D while
P(Q))
Orientatim,n
<< Q << 1/Re and the fractal
~1. According to Jennings,1 2 there
are two kinds of C-S-H structures formed from the same building blocks (globules), which pack
into structures with different specific surface area and density. SAXS detects both low-density C-
48
S-H (LD-CSH) and high-density C-S-H (HD-CSH) while SANS sees only LD-CSH. Therefore,
we shall use two different fractal dimensions to take into account this effect. We fixed xsAxs to be
0.064 for both C-S-H gels with and without additives, assuming the density of the calcium silicate
layer to be the same as that of the C-S-H particle in D-drying condition.14 This is reasonable
because the scattering length densities of PCEs are very close to water's SLD. Ideally, LSANS and
Lsaxs should be the same, but we allowed this parameter to relax a few angstroms, considering the
different resolutions of the two instruments. Also, we only fitted the Q-range of 0.02 A-1 <
Q<
0.70 A-1 and neglected the surface fractal effect in the Q-range chosen for the SAXS and SANS
data analysis. This is because the surface fractal feature is mainly present within the Q-range of Q
< 0.01
-'."'"4 Finally, because
the change of the
during the fitting process had little effect on
the inter-particle structure factor S(Q) in the range of
Q
> 0.02
A,
we fixed
at 670 A in
accordance with what is reported in previous studies."" 4
Figure 2.4.2- 1 shows the SAXS and SANS data fitting of pure C-S-H gel measured at 25 C
together with their corresponding S(Q) and P(Q). The difference between the SAXS and SANS
intensities comes from the different SLDs of X-ray and neutron, which contribute to P(Q). The
cartoons in Figure 2.4.2- 1(a) show the inter-globule fractal structure (pointed by the arrow to low
Q) and the intra-globule
sub-structure (pointed by the arrows to high Q). The comparison of SANS
and SAXS data fitting results for all of the samples is shown in Figure 2.4.2- 2. Our model agrees
with both SANS and SAXS data over the wide Q-range from 0.02 A-1 to 0.70
parameters used in Figure 2.4.2- 1 and Figure 2.4.2- 2 are listed in Table 2.4.2- 1.
49
A-1.
The fitting
(a)
102
o
SANS exp.
SANS fitti ag
0
SAXS exp.
-
101
-- SAXS fittilng
10'
4
10-1
10-2
7
f
/;
~
4i
10-5
101
104
100
10-1
10-2
10-3
0
o
A
A
10-
P(Q)
-
SANS
S(Q) -SAXS
P(Q) - SAXS
-
104
S(Q) -SANS
101
10-2
100
Q (A-i)
Figure 2.4.2- 1 Model fitting results of the pure C-S-H sample. (a) Experimental data of SAXS (blue open circle) and
SANS (black open circle) and the corresponding data fitting curves of SAXS (cyan line) and SANS (red line) of the
pure C-S-H sample. The SAXS experimental and fitting intensities are shift in y-axis by timing a factor 10 for clarity.
(b) inter-particle structure factor S(Q) of the SAXS data (blue solid triangle) and SANS data (black solid circle, not
seen because it is almost the same curve as the S(Q) of the SAXS data) and intra-particle structure factor P(Q) of the
SAXS data (green open triangle) and SANS data (red open circle) used to fit the data in panel (a). The difference in
P(Q) comes from the different x of neutron and X-ray. The error bars of the experimental data represent one standard
deviation. The cartoons in panel (a) show the fractal structure suggested by S(Q) and the multi-layered cylinder model
we use for P(Q).4
50
-
10
(a) SAXS
106
105
C-S-H
C-S-H/
10 4
PCE23-2
C-S-H/
10 3
102
101
Pure CSH (exp.)
CSH/PCE23-2 (exp.)
CSH/PCE23-6 (exp.)
O CSH/PCE102-2 (exp .)
0 CSH/PCE102-6 (exp .)
.
A
4
PCE23-6
C-S-H/
PCE102-2
C-S-H/
PCE102-6
100
10-I
102
10-3
104
1074
Pure CSH (fitting)
-
---
.
.
.
I
C-S-H
10
C-S-H/
104
PCE23-2
10 3
PCE23-6
102
PCE 102-2
C-S-H/
PCE 102-6
101
.
(b) SANS
106
a
CSH/PCE23-2 (fitting)
CSH/PCE23-6 (fitting)
CSH/PCE102-2 (fitting)
CSH/PCE102-6 (fitting)
C-S-H/
*+
C-S-H/
100
101
102
3
1-4
10
10
*2
101
-
1-
Q
100
(A-')
Figure 2.4.2- 2 Model fitting results of (a) SAXS data and (b) SANS data. Both panels show the experimental data
for pure C-S-H (black open square), C-S-H/PCE23-2 (blue open up-triangle), C-S-H/PCE23-6 (magenta open lefttriangle), C-S-H/PCE 102-2 (navy open diamond), C-S-H/PCE 102-6 (pink open hexagon), and the data fitting curves
for pure C-S-H (red), C-S-H/PCE23-2 (orange), C-S-H/PCE23-6 (cyan), C-S-H/PCE102-2 (green), C-S-H/PCE1026 (dark yellow). The experimental and fitting intensities are shifted in y-axis by timing factors of 104 (pure C-S-H),
103 (C-S-H/PCE23-2), 102 (C-S-H/PCE102-6), and 101 (C-S-H/PCE102-2) for clarity.4
51
Table 2.4.2- 1 Parameters extracted from the model fitting of SAXS and SANS data4 ,a
Sample
LsAxs
L2
n
R
DsAxs
Re
LsAzs
xsA's
DsANs
(A)
10.8(2)
-0.23(1)
2.83
CSH
(A)
13.16(3)
(A)
4.36(6)
0.86(1)
(A)
59.41(8)
2.71
(A)
31.0(1)
CSH +
12.15(1)
4.43(1)
3.51(1)
123.19(8)
2.85
78.5(1)
11.45(2)
-0.329(3)
2.47
12.44(1)
4.56(4)
1.43(1)
59.11(8)
2.47
36.0(1)
11.34(4)
-0.245(5)
2.62
12.76(2)
4.19(6)
1.01(1)
58.92(8)
2.69
32.3(1)
11.22(7)
-0.234(6)
2.54
12.64(1)
4.24(5)
1.46(1)
66.9(1)
2.51
39.5(1)
10.94(4)
-0.298(5)
2.60
PCE23-2
CSH +
PCE23-6
CSH +
PCE102-2
CSH +
PCE102-6
a 4 is fixed as 670 A 4 ,3 and yxa is fixed as 0.064, assuming the density of the calcium silicate layer to be the same as
C-S-H particle in D-drying condition. The width parameter Z of the number of layers with Schultz distribution is
collapsed onto the lowest boundary 0.01 set by the fitting process, indicating the wide distribution of n. DsAxs and
DsAs are found by fitting the SAS data in the Q-range of 0.0065 A-' < Q < 0.009 A-' through I = c * Q-D . Here we
allow LsAxs and LsANs to be different within a few angstroms to consider the difference of the instrument resolutions.
The thickness of calcium silicate layer L2 obtained from the SAXS data fitting is close to the result
of grand canonical Monte Carlo (GCMC) simulation (3.3-3.9
S-H gels (3.47
A). 3
A) 24'5 o
and SANS study on pure C-
The results show that the thicknesses of both the water layer (Li) and the
calcium silicate layer (L2) do not change much when PCEs are added, indicating that PCEs do not
form any intercalation products with this phase unlike the case of Al-rich hydrates, i.e. the AFm
phase.5' However, the additives enlarge the C-S-H globules in two ways. First, the average number
of repeating layers n increases for all of the samples with additives, suggesting that PCEs are able
to bind more layers together. Second, the globule disk radius R increases in samples with additives
of PCE23-2 and PCE102-6. This means that when adding PCE23-2 and PCE102-6, the
microstructure of C-S-H becomes
more like the continuous extension of branched or
interconnected multi-lamellar sheets, as in the models proposed by Dolado et al.25 ,2 6 and
McDonald et al.2 7 In addition, by fitting the SAXS data with I(Q) = Cp x Q- 4 in the range of 0.23
52
A-'
<
Q<
0.29 A-', where the contribution from S(Q) is negligible, we found that the Porod
constant C, (not shown), which is proportional to the total surface area per volume, has the trend:
C-S-H> C-S-H/PCE102-2> C-S-H/PCE23-6> C-S-H/PCE23-2> C-S-H/PCE102-6. This trend is
inverse to the trend of the effective radius Re of the globules (see Table 2.4.2- 1) except that the
sequence of PCE23-2 and PCE102-6 samples is reversed (they are very close to each other). This
is reasonable because particles with larger radius have smaller specific surface area. Surprisingly,
except for the sample with PCE23-2, the globules pack into a more open fractal structure when
additives are present, as shown by the decrease in fractal dimension D (see Table 2.4.2- 1).
Uchikawa et al.52 conducted atomic force microscope (AFM) measurements on Ordinary Portland
Cement with and without PCE and found that the addition of PCE significantly increases the
intensity and range of the steric repulsive force introduced by the additives. Ferrari et al.53
investigated the interaction of PCE23-6 with model surfaces using AFM, adsorption isotherms,
and zeta potential. The main tendency for PCEs in cement is to adsorb on positively charged
surface in order to avoid positive-negative particle aggregation. When particles do not adsorb SPs,
the electrostatic interaction dominates, otherwise the steric repulsion dominates. The enhanced
dispersion forces can explain the more open structure in the case of C-S-H (I) pastes containing
PCEs, where the particles all have the same charge as a result of the simplicity of the synthetic
phase which is almost free of Ca(OH)2. The more open structure can be also due to the more
disperse number of layers in the samples containing PCEs compared with the pure C-S-H (I)
sample. This can be seen clearly in Figure 2.4.2- 3, which shows the effective Schultz distribution
of the total thickness of the globules ( t = n L ), contributed from the effective distribution of the
number of repeating layers, for all the investigated cases. The high polydispersity of the globules
in the samples with PCEs makes the globules hard to pack into a compact structure. This is
53
consistent with our study on pure C-S-H gels, 3 in which we showed that C-S-H gel with lower
water content has a higher fractal dimension (a more compact fractal structure) and a more uniform
distribution with respect to the number of layers. Finally, we estimated the number density of the
globules NP (not shown) through the prefactor N = Np (Ap V,) 2 and found that NP has the trend
C-S-H> C-S-H/PCE102-2> C-S-H/PCE23-6> C-S-H/PCE102-6> C-S-H/PCE23-2 (i.e. the
reverse of the particle size trend). This is expected because with the same amount of C 3 S, the gel
with larger globule size should have lower globule number density. The lower Np can also explain
the more open fractal structure formed by the samples in the presence of additives.
1.0
\
--
Pure CSH
-- - CSH/PCE23-2
S.8-
---
o-
*
1
CSH/PCE23-6
-CSH/PCE102-2
-CSH/PCE 102-6
0.6
0.4
N
0 0.2
0.00
25
50
75
100
125
150
Total Thickness t (A)
Figure 2.4.2- 3 The effective Schultz distribution of the total thickness t = n L of the globules for samples of pure
C-S-H (black line with solid square), C-S-H/PCE23-2 (red line with solid circle), C-S-H/PCE23-6 (green line with
solid up-triangle), C-S-H/PCE102-2 (blue line with solid down-triangle), C-S-H/PCE102-6 (magenta line with solid
left-triangle). The normalization condition is
fs (t) dt =
54
L .4
The thermogravimetric analysis performed on the pastes containing PCEs is shown in Figure 2.4.24 as derivative weight loss signal versus the temperature. A well-defined peak due to the polymer
decomposition is evident at around 400"C for the C-S-H/PCE102-6 and C-S-H/PCE23-6 samples.
For the cases of CSH/PCE102-2 and CSH/PCE23-2, this peak is barely distinguishable from the
base line. A second feature is shown at about 380 C in almost all cases. The estimated mass losses
due to the presence of adsorbed polymers (considered the baseline due to the degradation of the
inorganic phase) are 0.4 0.1% for C-S-H/PCE102-6 and C-S-H/PCE23-6 and 0.2 0.1% for C-SH/PCE102-2 and C-S-H/PCE23-2. These semi-quantitative observations are in agreement with the
literature, 31-37 confirming the higher propensity of the PCEX-6 series to be adsorbed on the
calcium silicate phase, as a result of the higher amount of charged carboxylic groups present on
the backbone.
55
-K--
C-S-H/PCE102-6
-Li- C-S-H/PCE23-6
-A- C-S-H/PCE102-2
-C>- C-S-H/PCE23-2
L)
0
4-J
a)
M
0
300
400
Temperature (*C)
500
Figure 2.4.2- 4 Detail of the thermogravimetric measurements, presented as derivative weight loss vs. temperature,
of the four C-S-H samples synthesized in presence of additives. The pure C-S-H sample (not shown here) gives a
smooth baseline showing no features in the reported temperature range and in particular at 380 and 400 *C. a
Ridi et al. 34 previously studied the hydration reaction of tricalcium silicate (C 3 S) in the presence
of the same four PCEs investigated in this study. Their results showed that decreasing PEO side
chain length and density increases the induction time. As a result, the induction time followed the
sequence of C3S/PCE23-6 > C 3 S/PCE23-2 > C 3S/PCE102-6 > C3S/PCE102-2 > pure C3S. Our
results here indicate that for the longer PEO chain cases, i.e. PCE102-Y series, the PCE with lower
56
side chain density (PCE 102-6) induces globules with a larger disk radius and a large average
number of layers. These globules pack into a more open fractal structure compared with the higher
side chain density sample (PCE102-2) and the pure C-S-H sample. This should be related to the
fact that a PCE with a lower side chain density has a higher adsorption on the C3S starting powder
-
as well as on the final C-S-H particles and hence affects more on the microstructure of C-S-H. 3 1
37 However, surprisingly, the PCE23-Y series (shorter PEO chain length) shows the reverse trend.
The higher chain density polymer (PCE23-2) induces the greatest change in the C-S-H
microstructure. Actually, C-S-H/PCE23-2 has parameters very different from the parameters of
other samples (see Table 2.4.2- 1) and the reason for this is not clear yet. A field emission scanning
electron microscope (FE-SEM) investigation was conducted to clarify this point. The FE-SEM
images displayed in Figure 2.4.2- 5 show that in the pure C-S-H sample (panels (a) and (b)), two
different morphologies are present: zones of fibrillar structures and areas with networks of foils
coexisting all over the sample. Working at a very high w/c ratio results in a very inhomogeneous
sample in respect of the morphology and the composition, as testified both by SEM images and
EDS analysis, which shows the broad range of Ca/Si ratio ranging from 1.6 to 2.0. On the other
hand, almost no sign of fibril is found in the samples containing additives (panels (c)-(j)), where
the main morphology consists of flat structures arranged in sponge-like networks. If we consider
closely these sponge-like features, it is clear that a more compact structure is achieved when the
PCEs are present in the pastes, which is consistent with the expectation that PCEs produce highperformance concretes with low porosity. Moreover, it can be observed that in the cases of PCE232, PCE23-6 and PCE102-6, the global morphology is more amorphous and compact than the other
cases. At this stage we have to remember that SEM and SAS techniques give complementary
information and pertain different dimensional ranges, rendering difficulty to reconcile the results.
57
An ultra-SAS experiment would allow us to link the extracted fractal dimensions to the actual
morphology in the micrometer dimensional range.
iN
3Wk W'
I.
-*4 S
Figure 2.4.2- 5 FE-SEM images of (a)-(b) C-S-H, (c)-(d) C-S-H/PCE102-2, (e)-(f) C-S-H/PCE102-6, (g)-(h) C-SH/PCE23-2, and (i)-(j) C-S-H/PCE23-6. Images on the left correspond to 25X magnification (bar = 1 pm) while
images on the right correspond to 75X magnification (bar = 200 nm). 4
58
I
2.4.3 C-S-H gels with Methylhydroxyethyl Cellulose (MEHC,
Culminal) Additives
The SAXS data and the corresponding fitting curves for the C-S-H and C-S-H/MHEC are reported
in Figure 2.4.3- 1. The parameters used for the data fitting are listed in Table 2.4.3- 1. Figure 2.4.31 indicates that the SAXS data of both C-S-H and C-S-H/MHEC can be fitted very well across 3
orders of magnitude in
Q
range (2.3*10-3 A-1 <
Q
< 0.74
A 1) using a model of polydisperse
multilayer disk-like globules packing into a fractal structure. This is consistent with previous
studies by some of the authors.3
4
The globule structure and morphology of C-S-H gel can also be tuned by using different types of
additives. 4 In order to stress this point, a C-S-H gel was grown in the presence of
methylhydroxyethyl cellulose (Culminal), an additive commonly employed by cement industry.
Table 2.4.3- 1 suggests that Culminal additive favors the formation of small C-S-H globules as
compared to the pure gel. The interaction of cellulose derivative with C-S-H primary units results
in a significant reduction in the disk radius and a slight decrease of the average number of layers
inside the globules. The interlayer distance L also becomes smaller while the thickness of calcium
silicate layer L2 is not changed. According to the literature, 54 cellulose ethers facilitate the extrusion
of cement paste. The higher mobility of the globules due to the reduction in the globule size may
contribute to explain this effect induced by the cellulose derivative. In addition, SEM images (see
Figure 2.4.3- 3) indicate that the foil-like morphology becomes less extended when adding
Culminal. The much smaller disk radius R found in C-S-H/MHEC hinders the globules from
packing into a continuous morphology with higher resistance to the extrusion process.
59
Since the building blocks pack into the fractal structure, the size, shape, and polydispersity of the
globules will definitely affect the resulting fractal arrangement described by mass fractal
dimension D and fractal cutoff . The large disk radius R of pure C-S-H suggests that in this case
the microstructure of the C-S-H gel is more like a continuous structure with planar pores as
proposed by McDonald et al.2 7 This continuous and extended planar structure can explain the
higher fractal dimension obtained in pure C-S-H. The inclusion of the Culminal in C-S-H gel has
the effect of reducing the extension of the planar structure and consequently achieve a more open
arrangement (a smaller D). Moreover, the analysis of SAXS data shows that adding Culminal can
enlarge the "fractal domain" (increase
4,
see Table 2.4.3- 1).
Figure 2.4.3- 2 illustrates the Schultz distribution of the total thickness t = n L of the multilayer
disk-like globules in C-S-H and C-S-H/MHEC. The small Zn (see Table 2.4.3- 1) found for both
cases indicates that the globules are very polydisperse. The averages of total thickness I = n L are
25.5
A
and 19.0 A and the standard deviations of total thickness o- = nL /(Z, +1)1/2 are 23.2
A
and 15.4 A for C-S-H and C-S-H/MHEC, respectively. Overall these results show the possibility
to control the size of the constituent globules and therefore to tune the macroscopic properties of
cement.
60
7
10
106
10
104
oo10.
0
102
100
10-
o
o
C-S-H (experiment)
C-S-H/MHEC (experiment)
10-2 -I
10~ 3
0'
I
I
10-2
1
Q (A-')
100
Figure 2.4.3- 1 Model fitting results of SAXS data for C-S-H (blue open circle) and C-S-H/MHEC (red open uptriangle). The corresponding data fitting curves are denoted by black lines. The experimental and fitting intensities for
C-S-H are shifted in y-axis for clarity. The error bars of the experimental data represent one standard deviation and
are smaller than the symbols. The fitted parameters used here are listed in Table 2.4.3- 1.5
Table 2.4.3- 1 Parameters extracted from the model fitting of SAXS data of C-S-H and C-SH/MHECS,a
Sample
D
#(A)
R (A)
L (A)
CSH
CSH+
2.881(1)
752.6(1)
128.468(2)
14.251(1)
2.757(1)
3000(ub)
49.612(1)
12.598(1)
SH+C
Zn
Re (A)
5.752(2) 1.790(1)
0.206(1)
68.096(5)
5.908(2)
0.521(1) 32.742(3)
L 2 (A)
ii
1.509(1)
MHEC
aThe values in the parenthesis are one standard deviation from the nonlinear least-squares fitting process. For C-S-H
sample,
_ P1 -- Ps collapsed to the lower fitting boundary 0.001 set by the author while for C-S-H/MHEC,X = 0.079
tA-
+0.001.
61
0.040
C-S-I I/MHEC
0.035
0.030
0
0.025
0.020
0.015
N
0.010
0.005
0.000
|
0
20
40
60
Total Thickness t (A)
80
100
Figure 2.4.3- 2 The effective Schultz distribution of the total thickness t = nL of the multilayer disk-like globules,
due to the distribution of the number of repeating layers n, for C-S-H (blue solid square) and C-S-H/MHEC (red solid
fs (t)dt =1. 5
circle). We assume no distribution of the disk radius R of the globules. The normalization condition is
0
Figure 2.4.3- 3 shows morphology of C-S-H and C-S-H/MHEC by SEM. C-S-H exhibits leafy or
sheet-shape objects arranging in a dense, laminar pattern as already reported in previous work."
For C-S-H/MHEC, the foil-like morphology appears less extended. It is known that additives of
cellulose ethers facilitate extrusion of final paste. 54 This is probably because C-S-H gel favors the
formation of smaller sheets in the presence of cellulose additives and is induced a "plasticizing
effect" on the final paste.
62
Figure 2.4.3- 3 SEM micrographs of: (a) C-S-H and (b) C-S-H/MHEC at magnification 90 kX. Scale bar is 200 nm.
6
63
2.4.4 C-S-H gels with Different Ca/Si Ratio
The SAXS data and the corresponding fitting curves for C-S-H with Ca/Si = 1.0 and C-S-H with
Ca/Si = 1.4 are reported in Figure 2.4.4- 1. The parameters used for the data fitting are listed in
Table 2.4.4- 1. Figure 2.4.4- 1 indicates that the SAXS data of both C-S-H gels can be fitted very
well across 3 orders of magnitude in
Q
range (2.3* 10-3
A-1
<
Q
< 0.74
A-)
using a model of
polydisperse multilayer disk-like globules packing into a fractal structure. This is consistent with
previous studies by some of the authors.3 4
The size of C-S-H disks can be tuned by controlling the Ca/Si ratio and this size is linked to the
final macroscopic cement properties. Comparing C-S-H with Ca/Si=1.0 and C-S-H with Ca/Si=1.4
shows that the increase of the Ca/Si ratio reduces the effective size of the globules (Re ~ 68
C-S-H with Ca/Si
=
1.0 and Re ~ 26 A for C-S-H with Ca/Si
=
A
for
1.4 as indicated in Table 2.4.4- 1).
The radius of the disk R becomes much smaller although the average number of layers n becomes
slightly larger in C-S-H with Ca/Si = 1.4. Moreover, the calcium silicate thickness (L 2 ) becomes
larger but the interlayer distance (L) turns out to be smaller when increasing the Ca/Si ratio. A
similar decrease in the interplanar distance of C-S-H with the increase in the Ca/Si ratio was also
highlighted in a recent study.5 6 Furthermore, He et al.55 studied the morphology of the C-S-H gels
prepared by the hydrothermal route at 95 C with different Ca/Si ratios using Scanning Electron
Microscopy (SEM). They found that gel with lower Ca/Si ratio (Ca/Si = 1) exhibits sheet shape
while C-S-H with higher Ca/Si ratio (Ca/Si > 1.3) displays fibrillar morphology at the microscale
level. The much smaller disk radius R found in C-S-H with Ca/Si = 1.4 may possibly explain why
it is hard for the globules in larger Ca/Si case to pack into a more planar and continuous
morphology at larger length-scale. It should be noted that SEM and SAXS probe the microstructure
64
of the gels in different size domains. The larger detectable size achieved in the present SAXS
experiment (~100 nm) is a tenth of the scale-bar of the SEM images studied by He et al.55
The increase of the Ca/Si ratio in C-S-H gel both have the effect of reducing the extension of the
planar structure and consequently achieve a more open arrangement (a smaller D). Moreover, the
analysis of SAXS data shows that increasing Ca/Si can enlarge the "fractal domain" (increase (,
see Table 2.4.4- 1).
Figure 2.4.4- 2 illustrates the Schultz distribution of the total thickness t = n L of the multilayer
disk-like globules in C-S-H with Ca/Si = 1.0 and C-S-H with Ca/Si = 1.4. The small Zn (Table
2.4.4- 1) found for both cases indicates that the globules are very polydisperse. The averages of
total thickness t = n L are 25.5
A
and 23.9 A and the standard deviations of total thickness
a = nL /(Zn +1)1/2 are 23.2 A and 15.7 A for C-S-H with Ca/Si = 1.0 and C-S-H with Ca/Si
=
1.4, respectively. Overall these results show the possibility to control the size of the constituent
globules and therefore to tune the macroscopic properties of cements.
65
106
105 1
104
10310 2
-
10'
O
100
o
o
10-'1
C-S-H Ca/Si=1.0
C-S-H Ca/Si=1.4
Ij
1010-2
*''''10'2
ul~ululI
100
10-3
Figure 2.4.4- 1 Model fitting results of SAXS data for C-S-H with Ca/Si = 1.0 (blue open square) and C-S-H with
Ca/Si = 1.4 (red open diamond). The corresponding data fitting curves are denoted by black lines. The experimental
and fitting intensities for C-S-H with Ca/Si = 1.0 are shifted in y-axis for clarity. The error bars of the experimental
data represent one standard deviation and are smaller than the symbols. The fitted parameters used here are listed in
Table 2.4.4- 1.5
Table 2.4.4- 1 Parameters extracted from the model fitting of SAXS data of C-S-H with Ca/Si =
1.0 and C-S-H with Ca/Si = 1.45,a
D
Ca/Si=1.0
2.881(1)
Ca/Si=1.4
2.530(1)
(A)
R (A)
L (A)
L 2 (A)
<n>
752.6(1)
128.468(2)
14.251(1)
5.752(2)
1.790(1)
0.206(1) 68.096(5)
1327(1)
30.837(1)
12.364(1)
7.319(3)
1.930(1)
1.308(1)
Zn
aThe values in the parenthesis are one standard deviation from the nonlinear least-squares fitting process.
Re (X)
25.724(1)
P P2
in both cases collapsed to the lower fitting boundary 0.001 set by the author.
66
-
Sample
s
0.035
+
0.030
Ca/Si=1.0
-C-S-H
-
-+-- C-S-H Ca/Si=1.4
-
0.025
-
0.020
0.015-
0.010-
Aj
0.005
-
N
-
0.000
0
20
60
40
Total Thickness t
80
100
(A)
Figure 2.4.4- 2 The effective Schultz distribution of the total thickness t = nL of the multilayer disk-like globules,
due to the distribution of the number of repeating layers n, for C-S-H with Ca/Si = 1.0 (blue solid circle) and C-S-H
with Ca/Si = 1.4 (red solid square). We assume no distribution of the disk radius R of the globules. The normalization
condition is ffs(t)dt =1.5
0
Figure 2.4.4- 3 shows morphology of both C-S-H gels investigated by SEM. C-S-H with Ca/Si =
1.0 exhibits leafy or sheet-shape objects arranging in a dense, laminar pattern as already reported
in previous work.55 C-S-H with Ca/Si = 1.4 displays a morphology similar to Ca/Si = 1.0 but the
foils are more polydisperse and there are coexistent tiny fibrils.
67
Ca/Si=1.4
b
_
R
is
t
s
r1
Figure 2.4.4- 3 SEM micrographs of: (a) C-S-H with Ca/Si = 1.0 and (b) C-S-H with Ca/Si = 1.4 at magnification 90
kX. Scale bar is 200 nm. 5
68
Chapter 3
Microstructure of Magnesium-SilicateHydrate Globules
3.1 Introduction
Although concrete is one of the most used construction materials by mankind (~10 km 3/year), its
production is still not optimized in term of C02 emissions. 57 As a result, the manufacture of cement,
i.e. the main binder phase in concrete, contributes more than 5% of all human-generated
greenhouse-gas release. 58 In this context, one of the main challenges in the cement industry is to
develop alternative binders which have similar mechanical robustness but generate less CO2
emissions. 59
Recently, a strong attention has been focused on hydraulic binders based on highly reactive
periclase (MgO). This oxide reacts with water and a silica source, forming an amorphous solid
phase (i.e. magnesium-silicate-hydrate: (MgO)X-SiO2-(H20)y abbreviated as M-S-H 60) responsible
for the structural arrest of the hydrated matrix ("setting" of cement). MgO-based
cements61-64
can
be obtained by partially or fully using magnesium silicates which replace the carbon-rich limestone
originally required in the CaO-based Portland Cement (PC) production process. 65 Therefore, the
productionprocess of MgO-based cements involves low or even negative C02 emissions ifpart of
the MgO reacts with CO2. Using magnesium silicates as raw materials to produce large amounts
of MgO is a realistic approach since they are very abundant on a global basis (magnesium
69
orthosilicate constitutes about 70% of the Earth's mantle). 66 Even though MgO-based cements
have the potential to transform a production route with one of the highest environmental impacts
to a eco-friendly production process, 67 they are not widely in use so far. This is mainly due to their
poor properties that need to be addressed before broadcasting a large use of MgO-based
cements. 63,64 For example, it is known that the mechanical response of MgO-based cements or
MgO-PC blends are usually inferior to those of PC alone 64 if not carbonated in special ways. 6 8 69
In this context, we studied the differences in the morphology and in the microstructure between
pure synthetic M-S-H,7 0 C-S-H gels (calcium-silicate-hydrate: (CaO)x-Si02-(H20)y), 49 and their
mixtures. C-S-H has a colloidal nature 1 ,12, 28 and is the main hydration product and the primary
binding phase in PC.6 5 We extended our study to the mixed C-S-H/M-S-H gel with Ca/Mg ratio
1:1 in order to understand the compatibility of the two hydrated phases at the nanoscale and
microscale levels. By combining wide- and small-angle X-ray scattering and electron microscopy,
we studied the multiscale structure of M-S-H, C-S-H, and the mixed samples from angstrom to a
few micrometers. The different microstructures evidenced in this study might explain the
dissimilarities in the mechanical properties between the MgO- and CaO-based cements and allow
us to build bottom-up model for novel eco-sustainable binders.
3.2 Materials
Pure M-S-H gel (sample MSH) was prepared through a double-decomposition synthesis according
to the method described by Brew and Glasser. 70 Stock solutions of sodium metasilicate
(Na2SiO3-4H 2O) and magnesium nitrate (Mg(N0 3) 2 6H2 0) were prepared. The solutions with
volume of 1:1 Mg:Si ratio were cooled to about 0 C and mixed by stirring in a two-necked round-
70
bottomed flask. The flask was kept in an ice-water bath under continuous N2 flux. The sodium
silicate solution was added first, followed by slow addition of the magnesium solution. The product
was warmed to ambient temperature and the precipitate settled readily, leaving a clear supernatant
solution. In order to remove residual sodium, the precipitate was washed (diafiltrated) with
deionized water under a N2 atmosphere (to avoid carbonation). At the end of the process, a small
fraction of the supernatant was analyzed for Na* concentration using flame atomic absorption
spectroscopy ([Na+] < 0.20
0.01 ppm) to ensure that the by-product NaNO3 was completely
removed by the washing procedure. The same procedure was used to synthesize C-S-H with Ca/Si
ratio equal to 1 (sample CSH) using calcium nitrate instead of magnesium nitrate. The mixed CS-H/M-S-H gel (sample Mixed) was synthesized using calcium and magnesium nitrate in order to
have a Ca/Mg ratio equal to 1.
Another M-S-H gel was synthesized starting from highly reactive solid MgO and silica fume (SF)
according to Cheeseman et al.63 (sample MSH*). A paste of 30 wt.% MgO and 70 wt.% SF with
water-to-solid ratio of 3 was prepared by adding a mixture of the solids to water and mixing the
paste for 15 min. This alternative method to synthesize M-S-H is very similar to the real hydration
process taking place in MgO-based cement pastes.
Table 3.2- 1 shows the labels used to refer to the investigated samples in this study. Achieved
elemental compositions for all the samples were measured using Energy-Dispersive X-ray analysis
(EDX).
71
Table 3.2- 1 Chemical composition of the different silicate hydrates investigated.5
Sample Label
Target composition
Chemical Route
MSH
Mg/Si=1
double-decomposition
MSH*
Mg/Si=1
solid oxides
CSH-A
Ca/Si=1
double-decomposition
Mixed
Ca/Mg=1, (Ca+Mg)/Si=1
double-decomposition
3.3 Analytical Form of Small-Angle X-ray Scattering (SAS)
Model
The SAXS absolute intensity for a gel with fractal structure consisting of metal (Ca or Mg) silicate
hydrate globules immersed in the solvent can be expressed in general as:
I(Q) = N(PQ))S(Q), + bkg
(3.3.16)
N is a pre-factor related to number density and average total contrast of scattering length density
(SLD) of the globules. S(Q), is the corrected inter-globule structure factor of the porous gel taking
into account of the effect of polydispersity. (P(Q)) denotes the normalized intra-particle structure
factor averaged over the distribution of the size and all possible orientations of the globules.
72
3.3.1 Inter-globule structure factor
Here we assume that the size, orientation, and position are all independent 7 ' and therefore S(Q),
can be expressed by equation (3.3.1.1).
S(Q)C =1+,(Q) [S(Q) -1],
2
S(Q)=1+N fdr 4 r2
. F(Q) is the particle form factor and
sin(Qr)
g(r)= 1+
Qr
=
1+
D
7(D+1)
D F(D -1)sin[(D -1)tan-'(Q
1
(QRe)D
sin[(D -1)tan-1(Q4)]
2
(D -1) [+ (Q ) (D-1)/2(Q
[i + (Q
)]
)-2 J(D1)/2
(3.3.1.2)
)
where 8(Q) = (F(Q))2 /(I F(Q)
(3.3.1.1)
45,46,47
with F(x) being the Gamma function.
The essential parameters of the inter-globular structure factor are the mass fractal dimension, D,
the fractal cutoff dimension, , and the equivalent radius, Re.
3.3.2 Intra-globule structure factor
The normalized intra-particle structure factor, i.e. (P(Q)) = (IF(Q)2), includes the size and shape
information of the globules and therefore is essential to distinguish the difference in the
nanostructure of the building block between the C-S-H and M-S-H gels.
73
3.3.2.1 C-S-H case
For C-S-H gels, (P(Q)) equals to (P(Q))
and its mathematical expression can be found
in section 2.3.
The fitting parameters of the intra-particle structure factor of the C-S-H samples are the disk radius,
R, the layer thickness of hydration water, Li, and the layer thickness of hydrated calcium silicate,
L 2, the scattering length density contrast ratio Z = 'i - Ps (pt, p2, and ps are scattering length
P 2 -Ps
densities (SLDs) of hydrated water, hydrated calcium silicate, and solvent, respectively), the
average number of repeating layers inside a globule, n , the width parameter Z, of the number of
layers described by a Schultz distribution. The equivalent radius Re in S(Q) can be calculated as
Re = (3iR2L / 4)(1/3>, where L = Li + L 2 is the interlayer distance, and the total thickness t can be
found by t = n L.
3.3.2.2 M-S-H case
In the M-S-H cases (see Figure 3.4.1- 1) the high-Q peak characteristic of the layered sub-structure,
which is the essential feature of the C-S-H samples, is not present. In addition, there is a broad
bump in the high-Q part of the SAXS pattern. These observations allow us to use a simple model
of polydisperse spheres to describe the intra-particle structure factor. We denote the normalized
intra-particle structure factor averaged over the radius of the polydisperse spheres as
(3.3.2.2.1)
P(Q))R = fP(Q, R)shere fs(R)dR ,
0
where
74
P(Q, R)
= 3[(sin(QR) - (QR)cos(QR)]
(3.3.2.2.2)
.
sphere(QR)3
We assume the distribution of the sphere radius to be Schultz distribution and therefore
R
ZR (3.3.2.2.3)
.fs(R)=
+1).
1 RZR exp j ZR_ R 1 'I/(ZR
The essential fitting parameters of the intra-particle structure factor of the M-S-H samples are the
average radius R of the spheres and the width parameter ZR of the Schultz distribution of the
.
sphere radius. The equivalent radius Re in S(Q) is equal to R
3.3.2.3 Mixed case
Based on the description above, we analyze the mixed sample through a combined model,
assuming that the interaction between C-S-H and M-S-H components is negligible at the lengthscale studied by SAXS (~1-2000 A). Consequently, we can express the scattering intensity of
SAXS by adding together the intensity contribution from both C-S-H and M-S-H components:
I(Q) = NCSH
P(Q))CSH S(Q)mCSH + NSH
(P(Q))H S(Q)mASH + bg,
(3.3.2.3.1)
The essential fitting parameters of the intra-particle structure factor of the M-S-H samples are the
average radius R of the spheres and the width parameter ZR of the Schultz distribution of the
sphere radius. The equivalent radius Re in S(Q) is equal to R.
75
3.4 Results and Discussion
3.4.1 Nanometer to submicron length-scale
Figure 3.4.1- 1 shows the SAXS experimental data and the corresponding fitting curves for MSH
and MSH* samples, using the C-S-H model of multilayer disk-like globules. The parameters used
for data fitting are listed in Table 3.4.1- 1. Although the experimental data and the fitting curves
have acceptable agreement, the big error bars of many parameters from the fitting process shown
in Table 3.4.1- 1 indicate that C-S-H model doesn't work well for the M-S-H cases. The absence
of the high-Q peak corresponding to the multilayer sub-structure makes the use of C-S-H model
on M-S-H samples very unconvincing. Moreover, experimental
evidence of multilayer
arrangement in M-S-H gels is completely missing. For these reasons, a model that polydisperse
spheres arrange themselves into fractal structure is used.
76
1 ft
10'
106
105
C.
M
'i
104
"PM(
10
-
.. yy
ma
1.1
'
10
10
-'
O
o
o
MSH (experiment)
MSH* (experiment)
102
10-3
102
100
10~'
Q
(A-)
Figure 3.4.1- 1 The SAXS experimental data for MSH (violet open circle) and MSH* (pink open diamond). The data
fitting curves using C-S-H multilayer disk-like model are denoted by black lines. The experimental and fitting
intensities are shifted in y-axis by timing a factor of 10 for MSH for clarity. The error bars of the experimental data
represent one standard deviation and are smaller than the symbols. The fitted parameters used here are listed in Table
3.4.1- 1.
Table 3.4.1- 1 Parameters extracted from the model fitting of SAXS data of M-S-H samples using
C-S-H multilayer disk-like modela
D
L2
L
n
R
X
Z
Re
MSH
2.950(1)
393.13(2)
4(10)
5.0(9)
1(28)
10.42(2)
0.001(lb)
7(12)
6(107)
MSH*
2.487(1)
804.1(2)
0.001(lb)
10(66)
1(2)
162.559(8)
0.001(lb)
10(ub)
52(122)
alb(ub) means that the fitting value collapses onto the lower (upper) boundary set in the fitting procedure. The values
in the parenthesis are one standard deviation from the nonlinear least-squares fitting process.
77
Figure 3.4.1- 2 shows the experimental data and the corresponding fitting curves for MSH and
MSH*, using polydisperse spheres as intra-particle structure factor. The fitting parameters used in
Figure 3.4.1- 2 are listed in Table 3.4.1-2. The match between the data and fitting curves for both
MSH and MSH* over the wide
Q
range indicates that the simpler model works very well to
describe the newly made M-S-H samples. The structure difference of the basic building block can
lead to totally different mechanical properties. The binding force between disk-like globules in CS-H is stronger than that between spherical globules in M-S-H because C-S-H globules have
surface contact while M-S-H globules have only point contact. It is noteworthy that our work is
the first time that the structure of M-S-H gels is investigated in such a detail.
Table 3.4.1- 2 evidences that the average radius R of the spherical globules is about the same for
MSH and MSH* (R
~ 17
A).
However, the size distribution of the globules is wider in MSH.
This can be seen from the Schultz distribution of the radius R illustrated in Figure 3.4.1- 3. The
standard deviations of the radius distribution
-R = R I(ZR + 1)1/2 are 9.7
A and 6.8 A for MSH and
MSH*, respectively. In addition, the larger fractal dimension D for MSH indicates that the
globules arrange compactly in the fractal structure as compared to the MSH* case. Masoero et
al.72 also found an increase in packing density with polydispersity in cement composed of spherical
building particles.
78
Table 3.4.1- 2 Parameters extracted from the model fitting of SAXS data of CSH, MSH, MSH*
and Mixed samples','
R (A)
L (A)
L2 (A)
nZ
752.6(1)
128.468(2)
14.251(1)
5.752(2)
1.790(1)
2.608(1)
403.5(2)
b
13.85(1)
b
b
D
()
R(A)
MSH
2.971(1)
374.38(2)
17.414(1)
-
-
-
2.232(1)
-
MSH*
2.753(1)
443.46(2)
16.482(1)
-
-
-
4.879(1)
-
-
CSH
2.881(1)
Mixed
Mixed
3(ub)
28.86(5)
b
-
-
-
b
NcSH
NMSH
365.6(2)
2.614(1)
-
Mixed
P2 - Ps
0.206(1)
b
Re (A)
0.001(lb)
68.096(5)
b
b
ZR
-
D
(A)
-
Sample
alb (or ub) means the fitting value collapses onto the lower (or upper) boundary limit. The values in the parenthesis
are one standard deviation from the nonlinear least-squares fitting process. bOther structural parameters of Mixed
shown in equation (3.3.2.3.2) are fixed as the same values as CSH and MSH.
79
10i'I
10'
106
10104
-
*
0%PO
103
10'I
1:
o
O
10-1
10-2
MSH (solution)
MSH (solid)
51
,1
10-3
10-
1
10-'
100
)
Q (A4
Figure 3.4.1- 2 Model fitting results of SAXS data for MSH (violet open circle) and MSH* (pink open diamond),
using polydisperse spheres as intra-particle structure factor. The data fitting curves are denoted by black lines. The
experimental and fitting intensities are shifted in y-axis for MSH for clarity. The error bars of the experimental data
represent one standard deviation and are smaller than the symbols. The fitted parameters used here are listed in Table
3.4.1- 2.5
80
0.07
(solut -ion)
-\ -MSH
-
0.06
-+-MSH*(solid
+
-
0.05
0
-
0.04
0.03
-
-
*
-
0.02
-
*
0.01
*
U.',
0
I
5
I
10
I
-
15
20
*
I
I
25
30
35
40
45
50
55
60
R (A)
Figure 3.4.1- 3 The Schultz distribution of the radius R of the spherical globules for MSH
(violet solid circle) and
.
MSH* (pink solid diamond). The normalization condition is ffs (R) dR
=1
0
Figure 3.4.1- 4 shows the experimental SAXS data and the corresponding
fitting curves for CSH,
MSH and Mixed samples, in which the fitting model for CSH is polydisperse multilayer
disk-like
globules, that for MSH is polydisperse spherical globules, and that for Mixed is the combined
model described in equation (3.3.2.3.1). The fitting parameters used in Figure 3.4.1- 4 are listed
in
Table 3.4.1- 2. Interestingly, the fractal cutoff
found in M-S-H samples (MSH and MSH*) is
much smaller than that found in CSH. This suggests that the fractal structure expands narrower in
81
space (the "fractal domain" is smaller) in M-S-H case. The much larger fractal size found in C-SH indicates a stronger binding force between the globules to maintain and expand a larger fractal
domain. The fractal dimensions of CSH and MSH are both very large, suggesting that compact
fractal structures can be achieved by double-decomposition in solutions. However, D is higher in
the MSH case. This corroborates that it is easier to pack into compact structures for spheres than
for disks. Cho et al.73 studied the effect of particle shape on packing density in natural and crushed
sands. They found that irregularity (i.e. decreasing the sphericity or roundness of the particles) can
hinder the particle mobility and therefore make the particles hard to arrange themselves into a
dense packing configurations. Although the particles they investigated are much bigger in size
than the globules we studied here, the basic packing mechanism should be similar.
82
108
A
M-S-H
Mixed
o
C-S-H
o
107
106
105
0,
104
4)
102
102
4)
Ana
10
100
102
10"2
10~3
10-'
10-2
100
Q (A-)
Figure 3.4.1- 4 Model fitting results of SAXS data for CSH (blue open diamond), MSH (red open circle), and Mixed
(olive open up-triangle), and the corresponding data fitting curves are all denoted by black lines. The experimental
and fitting intensities are shifted in y-axis for MSH and Mixed for clarity. The error bars of the experimental data
represent one standard deviation and are smaller than the symbols. The fitted parameters used here are listed in Table
3.4.1- 2.1
83
There is still a peak of layered structure at high
Q in the
SAXS data for the Mixed sample even
though it is broader than the peaks in the case of C-S-H samples, as shown by Figure 3.4.1- 4. In
addition, the peak for the Mixed sample is superposed by a broad shoulder characteristic of
polydisperse spheres. Furthermore, the SEM image of the Mixed sample (see Figure 3.4.3- 1)
suggests the decoupling of C-S-H and M-S-H morphologies. We therefore fitted the SAXS curve
of Mixed sample by linear combination of the curves of the pristine CSH and MSH gels, which
were synthesized using the same chemical route, assuming that the interaction between the C-S-H
and M-S-H fractals is negligible (see equation (3.3.2.3.1)). We only allowed change of pre-factors
NCSH and NMSH and fractal parameters DCSH, CSH, DMSH, and MSH. The interlayer distance LCSH was
set as a variable to account for the slight change of the peak position, however it does not change
much compared with L of CSH. The fitting parameters are listed in Table 3.4.1- 2. Figure 3.4.1- 4
demonstrates the high agreement between the SAXS data and the corresponding fitting curve based
on this combined model. The results show that the fractal dimension D of both C-S-H and M-S-H
components does not change much in Mixed sample compared with D in the pure counterparts,
CSH and MSH. Nevertheless, the fractal cutoff 4 of both components decreases significantly. The
result suggests that both kinds of globules pack into similar fractals as those in their pure
counterparts but the fractal domains become much smaller when the other component is present.
3.4.2 Angstrom length-scale
Figure 3.4.2- 1 shows the wide-angle X-ray scattering (WAXS) data for CSH, MSH and Mixed
samples. There are sharp peaks in WAXS patterns for CSH located at
Q=
2.05
A-1
and 2.23
A-1
characteristic of Tobermorite Ca5(Si6O16(OH) 2).4(H 20) (see ref.55 and the references therein),
indicating formation of a quite ordered structure at the angstrom level. In contrast, the broad bumps
84
of MSH centered at
Q=
1.84 A-' and 2.45
A- 1 suggest
that Lizardite 4 3 may form in M-S-H gel
although the phases present in the gels are mostly amorphous in nature. WAXS patterns indicate
that Brucite, Mg(OH)2, is not present in the final product of MSH because of the absence of
characteristic peaks located at
Q=
1.28, 1.97, 3.51, 4.01, and 5.18 A-.
64
The WAXS data for
Mixed sample contains features of both C-S-H and M-S-H components as the pattern is the
superposition of C-S-H sharp peaks and M-S-H broad shoulders.
50000
M-S-H
-#--
45000 -
a
E
--Mixed
#
C-S-H
40000
35000-
3000025000200000
15000
10000
-
5000
1.0
1.2
1.4
1.6
1.8
2.0
Q
2.2
2.4
2.6
2.8
3.0
3.2
3.4
(A-')
Figure 3.4.2- 1 WAXS data for CSH (blue), MSH (red), and Mixed (olive). "*" indicates the peaks attributed to
Tobermorite Cas(Si 6 Oi 6 (OH) 2 ).4(H20) 38 and "#" denotes the peaks contributed by Lizardite (Mg 3Si 20s(OH) 4). 74 The
WAXS intensities are shifted along the y-axis for the sake of clarity. 5
85
3.4.3 Submicron to micrometer length-scale
Figure 3.4.3- 1 shows the SEM images for CSH, MSH and Mixed samples. The SEM image of
MSH shown in Figure 3.4.3- 1(b) evidences an irregular porosity between interconnected and
densely packed spherical particles (diameter between 30 and 50 nm) at the submicron level. It
seems that difference in structure between the basic building blocks of C-S-H and M-S-H reflects
disparity in morphology at larger length-scale. CSH exhibits laminar pattern while MSH shows
morphology of connected spheres at submicron to micrometer length-scale. The extended structure
of C-S-H suggests a stronger binding force and better mechanical properties because the foil-like
objects in C-S-H have surface contact rather than point contact between the spherical particles
found in M-S-H gel. Finally, the case of Mixed gel is particularly interesting. This sample presents
regions of typical M-S-H structure alternating with regions of characteristic C-S-H morphology.
This mixed feature is in agreement with the WAXS and SAXS results (see Figure 3.4.2- 1 and
Figure 3.4.1- 4). Co-precipitated M-S-H and C-S-H are essentially immiscible as a result of
intrinsic structural differences between the two hydrated phases from angstrom to micrometer
length-scale.
86
CSH
a
MSH
b
r4
Mixed
c
Figure 3.4.3- 1 SEM micrographs of: (a) CSH and (b) MSH (c) Mixed at magnification 90 kX. Scale bar is 200 nm.
.5
87
Chapter 4
Microstructure of Pluronics Micellar
Solutions
4.1 Introduction
Pluronics is a type of triblock copolymers with a central polypropylene oxide (PPO) block and two
polyethylene oxide (PEO) blocks, each on either side of PPO block. It has attracted lots of interest
recently because of its immense industrial applications in drug delivery, biotechnology, detergency,
tissue engineering, food protection, coating and painting. 75-88
When Pluronics is dissolved in solution, it exhibits very rich phase behavior. The properties of
Pluronics solutions are significantly influenced by temperature and concentration through
adjusting their hydrophobic/hydrophilic character.89-92 The Pluronics exhibits self-assembly
feature because of the different solubility for the constituent blocks. 89- 9 1 At temperature below the
critical micelle temperature (CMT), both PEO and PPO blocks are soluble and therefore the
copolymers stay as unimers in the solution. As increasing temperature above CMT, PPO block
starts to become hydrophobic and the copolymers assemble to form micelles with hydrophobic
PPO core and hydrophilic PEO corona. 90 When further heating, the solutions reach a threshold
temperature named cloud point and the system forms two coexisting isotropic phases. 93-95 At
higher concentration and temperature, micelles can form gel state and crystalline lattice
structure.
96,9 7
88
The phase diagram of Pluronics copolymers has been widely studied by small-angle neutron
scattering (SANS),
98-1 02
small-angle X-ray scattering (SAXS),
101'103,104
static and dynamic light
-
991 0 1
105
scattering (SLS and DLS), nuclear magnetic resonance (NMR), rheological measurement,
103,106,107
and differential scanning calorimetry (DSC).1 0 1,10 8 109 However, there are very limited
understanding on the solvent distribution within the micellar particles formed by Pluronics
copolymers, which is the key to unravel the role of the solvents in structural stability of the micelles.
Recent studies have shown that dehydration of the hydrophilic component at high temperature
leads to clouding behaviors. Moreover, it was suggested that gelation of Pluronics solutions is a
result of dehydration of the micellar cores.
10
It is therefore important to understand the instability
of the micelles induced by change of the solvent distribution in order to further current
comprehension of the phase behaviors of Pluronics and other amphiphilic copolymers. On the
other hand, since many drugs are hydrophobic and are sensitive to water distribution within the
carrier, studies on hydration distribution can provide essential information to the controlled release
drug delivery systems based on amphiphilic copolymers.
The lack of knowledge of hydration distribution is mainly due to the technical difficulty in
conducting experiments and data analysis. In previously SANS experiment, Cap and Gown
model 1 ,12 was used to describe the shape and size of the Pluronics micelles. In this model,
volume fraction of water is treated as a constant value inside the micelle core and follows Gaussian
distribution outside the core. However, with the broadness of the accessible wave vector
Q range
due to the advance of SANS instrument, this model cannot obtain fitting curves with satisfactory
agreement at high
Q region. A modified model
and solvent distribution"
Li et al."
5
5 should
1 114
taking account of interaction of corona chains 3,
be used instead in order to attain more accurate results. Recently,
developed a method to extract solvent distribution within the micelles using SANS
89
contrast variation based on core-shell model. This method was successfully used to determine
water distribution inside micelles consisting of polystyrene- poly[styrene-g-poly(ethylene oxide)]
diblock copolymers." 5 Li et al. focused on the effect of PEO side chain length on water distribution.
In this study, we applied this method to investigate the degree and distribution of hydration within
the Pluronics micelles under the influence of molecular weight, temperature, concentration, and
hydrophobic/hydrophilic character, which are all essential parameters for tuning the phase
behavior. Our results reveal strong relation between these parameters and the hydration and
indicate an important role of the solvent molecules in the micellar solutions formed by amphiphilic
copolymers.
4.2 Materials
The L64, P84, F88, and F108 Pluronics triblock copolymers were purchased from BASF Corp.,
Florham Park, NJ, USA and were used as received without further purification. The details of the
Pluronics are described in Table 4.2- 1. D2 0 were purchased from Cambridge Isotope Laboratories,
Inc., Tewksbury, MA, USA. Solvents for SANS contrast matching experiments were prepared by
mixing appropriate amount of D2 0 with de-ionized water. Four different solvents with molar ratios
of D 2 0/H 2 0 at 100/0, 90/10, 80/20, and 70/30 were used. The samples of different concentrations
were prepared by dissolving appropriate amount of copolymers in the four solvents in order to
have four contrasts. The samples were stored for one week at 4 "C, which is below the critical
micelle temperature (CMT), for homogeneous mixing.
90
Table 4.2- 1 Properties of PEO-PPO-PEO Triblock Pluronics Copolymers Used in this Work
Pluronics
Molecular Weight
No. of PO
No. of EO
PO/EO
30
2*13
1.15
Classified Type
(g/mol)
L64
2900
A
(Hydrophobic)
P84
4200
43
2*19
1.13
F88
11400
39
2*103
0.19
A
(Hydrophobic)
B
(Hydrophilic)
F108
14000
48
2*127
4.3 Analytical Form of Small-Angle
0.19
B
(Hydrophilic)
Neutron Scattering
(SANS)
In order to extract the intramicellar water distribution together with the polymeric spatial
arrangement, we incorporate the contrast variation method into the SANS technique developed by
Li et al. ,1" 5 assuming the isotopic effect can be neglected.
The measured SANS absolute intensity I(Q) can be obtained by convoluting the theoretical
coherent scattering cross section Ith(Q) with the instrumental resolution function R(Q), expressed
as:
I(Q)=J 2t (Z)
2-
()2
exp
_
(QQ)
215(Q)
2
(4.3.17)
_dz,
As shown in equation (4.3.1), R(Q) is assumed to be a Gaussian function with standard deviation
6(Q) and
Q dependent parameter
Qm. Here, we approximate our micellar system as monodisperse
91
centrosymmetric core-shell particles with diffusive interfaces interacting with each other through
hard sphere potential."
6
With this approximation, Ith(Q) can be further factorized into the
contributions from the intraparticle density fluctuation and from the interparticle spatial
arrangement, expressed as:
Ith(Q)
(4.3.18)
=AP(Q)S(Q)+IINc
where A is a prefactor depending on particle number density and the total particle scattering
contrast, P(Q) is the normalized intraparticle structure factor, which is the Fourier transformation
of the distribution of the scattering length density (SLD) within the micelle, S(Q) is the interparticle
structure factor, and IINC is the
Q independent
incoherent background.
4.3.1 Intraparticle Structure Factor
To characterize the intraparticle spatial correlation of both polymeric component and the
surrounding solvent, we model the intramicellar SLD distribution Ap(r) as a centrosymmetric
core-shell particle with diffusive interfaces at both core-shell boundary and micellar peripheral
boundary. The degree of the fuzziness of the interfaces is approximated by two Gaussian functions.
I
Therefore, the P(Q) can be expressed as:
2
(P2 - P1 )2
_(P2 - 11 )2
(P2
+
A
P V
- PI)V2 +
Q VR
+ ab Pblob(Q,
Fi (Q, R2) exp(_
2)
,115
4
V
F (Q, RI)exp(-
Q2
+
P(Q) = F(Q,R R2 , c1,C02) + ab Pio(Q,Rg)
2
4
R,)
92
where pi (p2) is the SLD contrast between the shell (core) and the solvent, i.e.,
P1 = Pshel
-
Psoivent
and P 2
= Peore - Psoivent
the radius of the micelle (core), 61
(c2)
- Vi (V 2) is the volume of the micelle (core), Ri (R 2 ) is
is the standard deviation of the Gaussian function used to
describe the fuzziness of the interface, and F(Q,R) is the normalized form factor of a
homogeneous sphere:
F (Q1R)
3[sin(QR) - QR cos(QR)]
(43
. .1
4)
.
-
(QR)
Pblob(Q,Rg)
is the contribution from blob scattering, 113,114 which can be calculated from the model
of Beaucage."1 4
sin[ptan-1(q*)
ua
1+
~2
/2
(4.3.1.5)
'
1
Pblob (Q, Rg) =
1qb
and p = v-1 -1. v is the Flory-Huggins parameter.
where q* =
[erf(qRg /
Nf)
The radius of gyration Rg of the micelle can be calculated by its definition:
fr2p
R
r)d3r
P(- r
V F2 (Q,R ,R25O,
2)
F2 (Q, R1, R2,9 al5,U2)I
U
(4.3.1.6)
+5U)]
(P P()22
PV (P2 -P1 )V2 +P1 Vi 2
115
The prefactor A can be explicitly calculated by:
93
A=n[(p2 -P1 )V2 +pvi] 2
(4.3.1.7)
where ns is the micellar number density.
Since the scattering length contrast profile Ap(r) is the difference between the SLD of the micelle
and that of the solvent, we can extract the number density distribution of the hydration water H(r)
by noting that both polymeric components and the guest water molecules contribute to the micellar
SLD. Thus, we express Ap(r) as:
Ap(r)
= pmicele(r) - Psovent = ppoymer(r) +
H(r)- bsolvent
- Psolvent
(4.3.1.8)
= Ppoiymer(r)+ bsolven{ H(r)
where bsolvent is the average scattering length of the solvent and psolvent the average SLD. bsolvent and
psolvent can be calculated by:
(4.3.1.9)
bsovent = y - bDO + (1- r)bH2o,
and
(4.3.1.10) Pso1ent
=
b
V water
where y is the molar ratio of D20 in the solvent and Vwater is the water molecular volume, which is
30 A 3
.
_soivent
PD
2O
2OH
Here we neglect the number of the labile protons in the Pluronics copolymer. Therefore, ppolymer(r)
is unchanged when varying y. We can determine the value of ppolymer(r) and H(r) uniquely through
fitting Ap(r) versus y at each radial distance r with equations (4.3.1.6) and (4.3.1.7).
Based on the discussion above, the prefactor A can be re-written to
94
A
= nl
Naggb,,.oer+ YNex Nagg(bD
bH
NaggPY""bH2
Do
bH]]2(4.1.1
2
where Nagg is the aggregation number of the copolymers in a micelle, Nex is the number of protons
in a copolymer chain which are exchangeable with hydrogens or deuteriums the solvent. bpolymer
and vpolymer are the total scattering length and total volume of a copolymer, respectively.
4.3.1 Interparticle Structure Factor
S(Q) is obtained by solving the Ornstein-Zernike integral equation analytically with the PercusYevick closure." 6 Hard sphere interaction potential was used in this study which has shown to
provide satisfactory results for soft colloidal systems at low concentration.1 08
95
4.4 Results and Discussion
The SANS contrast variation data analysis results for all the samples at various conditions are
listed in Table 4.4- 1. Other relative parameters extracted from the hydration analysis are listed in
Table 4.4- 2.
Table 4.4- 1 Parameters Extracted from Global Model Fitting of SANS Data of PEO-PPO-PEO
Triblock Pluronics Copolymers Used in this Worka
Sample
T
(P
( 0C)
R
Rin
Rout
(A)
(A
(A
Uc
(A)
(A)
X100
X90
X80
X70
am
cc
c
40
0.015(6)
55(8)
38.5(5)
53.8(7)
0.01 (b)b
21.1(8)
2.26(9)
2.22(9)
2.17(9)
2.06(9)
0.05g/ml
40
0.0581(3)
121.0(3)
24.2(7)
41.9(6)
0.01 (lb)b
17.4(4)
1.31(5)
1.35(5)
1.36(5)
1.42(5)
0.O1g/ml
40
0.0159(4)
152(3)
37.9(2)
51.2(5)
0.01 (lb)b
21.2(4)
1.42(3)
1.44(4)
1.47(4)
1.53(4)
0.F8ml
50
60
70
80
80
0.2030(3)
0.2147(3)
0.1951(2)
0.1701(3)
0.0386(8)
191.5(1)
198.8(1)
201.7(1)
199.8(1)
232(3)
31.73(3)
34.51(2)
37.09(3)
38.82(3)
42.2(1)
73.6(4)
78.0(3)
81.6(3)
77.7(4)
11.4(1)
35.9(3)
5.8(1)
5.9(1)
6.0(1)
6.3(1)
10.78(9)
11.98(8)
11.24(9)
35.6(3)
33.8(3)
37.1(3)
5.00(7)
4.84(7)
3.40(6)
5.06(7)
4.84(7)
3.37(6)
5.38(8)
5.36(8)
3.82(7)
5.36(8)
5.12(7)
83(2)
11.3(3)
49(1)
3.0(2)
3.1(2)
3.1(2)
F108
gml
0.01
0.
ml
0.8ml
____
___
-
0.016/ml
3.1(2)
___
40
50
60
70
0.2188(4)
0.2531(3)
0.2412(3)
0.2132(3)
223.6(2)
238.0(1)
243.1(1)
238.9(1)
34.20(2)
37.25(2)
39.30(2)
40.99(2)
85.2(5)
10.8(1)
42.5(5)
7.2(2)
7.9(2)
8.0(2)
8.0(2)
94.4(3)
93.8(3)
92.7(3)
11.38(7)
10.98(6)
11.59(6)
40.5(3)
43.6(3)
42.8(3)
5.32(6)
4.66(5)
7.46(9)
5.97(6)
5.03(6)
7.52(9)
5.86(6)
5.09(6)
7.59(9)
6.00(6)
5.06(6)
80
0.1817(3)
232.3(2)
42.70(4)
94.0(3)
13.20(7)
39.3(3)
-
4.97(6)
5.04(6)
5.04(6)
6.67(4)
6.72(4)
13.66(3) 27.4(1)
0.4781(2) 204.63(3) 42.85(2) 91.4(1)
80
aThe values in the parenthesis are one standard deviation from the nonlinear least-squares fitting process.
6.92(4)
7.11(4)
bib means the fitting parameter collapses onto the lower fitting boundary set by the author.
cX100, X90, X80
and X70 are the values of Pcore
Pshell
- Psolvent
-
for
100%, 90%, 80%, and 70% D 20 solvents, respectively.
Psolvent
96
Table 4.4- 2 Parameters Related to Hydrationa
Sample
(bC)
Naggb
Sam___le___(__C)____agg_
R C
HtotaRd*1
(A
p(0-8
A-3)
totalR
1toaP
/ Na
ns *HtotalRp
/Ngg
(1022 Cm
40
98(13)
99.8
1.35
17(10)
1374
2.32
40
0.05g/ml
P84
40
0.Olg/ml56)
21(2)
56(1)
107.9
1.60
6.26(6)
7607
1.00
131.8
13.
2.90
0.86(6)
5186
2.51
32(1)
190.5
9.46
5.52(1)
29571
5.22
60
44(1)
195.8
10.24
5.22(1)
23275
5.34
70
58(1)
194.7
10.02
4.541(8)
17271
4.55
80
67(2)
204.4
11.59
4.071(9)
17303
4.72
80
78(5)
251.3
21.67
0.59(3)
27779
1.28
0.ml
40
49(1)
221.2
14.86
3.7(1)
30333
5.56
0.05ml
50
67(1)
225.9
15.76
3.59(5)
23524
5.65
60
93(2)
237.9
18.38
3.21(4)
19762
5.89
70
84(2)
235.2
17.73
2.99(6)
21112
5.30
80
94(2)
225.9
15.63
2.77(7)
16631
4.33
80
42.2(1)
181.2
8.01
10.7(5)
18972
8.53
0.Og/ml
0.5
0.8ml
5ml
0
3
aThe values in the parenthesis are one standard deviation.
bAggregation number Nagg is found by fitting the fitted prefactor A with equation (4.3.1.9). For 0.05 g/ml L64 and 0.01
g/ml P84 at 40 0C, Nagg value is calculated by Nagg = (4/3 7c Rtn 3)/(vpo Npo) due to their "dry" micelle core found in
Figure 4.4.4- 1(b) in order to avoid unnecessary fitting process which delivers large errors. vPo= 95.411 is the volume
of one PO monomer and NPo is the number of PO monomers in one triblock copolymer.
.
cRadius of periphery Rp is the closest distance to the micelle center where water number density equals to 0.033 A-3
1/vwater= 1/30 A-3 , the bulk water number density. That is, H(Rp) = 0.033 A- 3
Rp
JH(r) 47rr2 dr
.
d Htotal,Rp is the total number of water within a sphere with radius equals to R,. Htotal,Rp =
0
ens is the micelle number density and is calculated by ns = 6(p/(7r R3 ), where
and R is the hard sphere radius of the micelle particle.
97
p is the volume fraction of the micelles
4.4.1 Effect
of
Molecular Weight
Figure 4.4.1- 1 (a) and (b) show the experimental SANS data and their corresponding fitting curves
in four solvents of different D 20 concentrations for 60 "C 0.05 g/ml F88 and F108 micellar
solutions, respectively. The data was subtracted by constant incoherent backgrounds. The data
exhibit clear core-shell features of two bumps for the micelles formed by hydrophobic PPO core
and hydrophilic PEO shell. These features enable us to accurately determine the fitting structural
parameters as indicated in Table 4.4- 1. Some relevant parameters calculated from Table 4.4- 1
and hydration results are listed in Table 4.4- 2. The structural parameters such as R, Rin, Rout all
have larger values in F 108 due to its larger molecular weight. The greater size of F 108 micelles is
also because of its large aggregation number Nagg (see Table 4.4- 2) compared with the F88 case.
Figure 4.4.1- 1(c) demonstrates the neutron scattering length density (SLD) distribution p(r) of
F88 (dashed lines) and F108 (solid lines) of the hydrated micelles at different contrasts extracted
from the SANS model fitting. The SLD contribution of the polymeric component ppolymer(r)
(orange lines in Figure 4.4.1- 1(c)) and the number density of hydration water (Figure 4.4.1- 1(d))
can be determined by linear fitting through equation (4.3.1.6). The high polymeric SLD of F 108,
and therefore high polymeric density, compared with F88 is the combined effects of high Nagg
(Table 4.4- 2) and low degree of hydration (Figure 4.4.1- 1(d)). Figure 4.4.1- 1(c) and (d) indicate
that the core-shell interfaces in F88 and F108 are not sharp interface and both polymer density and
water number density change smoothly. Moreover, water density distribution and therefore water
volume fraction within the PPO core is not a constant in type B Pluronics as suggested by previous
Cap and Gown model 1 1,11 2 (core radius Rin for F88 and F108 at 0.05 g/ml at 60 "C is 34.5 A and
39.3
A,
respectively).
Figure
4.4.1-
1(d)
suggests
that
at
fixed
PO/EO
ratio
(hydrophobic/hydrophilic ratio), water molecules are easier to diffuse into the micelles formed by
98
Pluronics with lower molecular weight for type B Pluronics. This can be seen clearly from Table
4.4- 2. Rp, periphery radius, is the distance to micelle center where water number density starts to
be comparable to bulk water number density.
Hotal,Rp, the
total number of water within a sphere
with radius Rp, is 10.24 * 105 and 18.38 * 10 5 for F88 and F108, respectively. However, Htotal,Rp/
Nagg = 23275 and 19762 for F88 and F108. This means that although more water molecules are
contained in single micellar particle for F 108 solution because of its large particle size contributed
from the large Nagg and molecular weight, the number of water molecules per single triblock
copolymer chain is greater for F88. This is due to the longer distance required by the water
molecules to travel through which hinders the diffusion. This is suggested from Figure 4.4.1- 1(d).
F88 and F108 have comparable water number density in corona region but the density difference
enlarges when approaching to the micelle center since fewer water molecules are able travel
through the long PEO chain into the core region for large polymer such as F 108. The value
ns*HtotalRp
represents the total number of waters stay in the micelle particles per unit volume,
where ns is the number density of the micelles. ns*Htotal,Rp is 5.34 * 1022 and 5.89 * 1022 for F88
and F108 at 0.05 g/ml at 60 C, respectively. Surprisingly, at the same concentration, i.e. the same
amount of EO and PO monomers because of the same PO/EO ratio for F88 and F108, there are
slightly more water retained in the micelles in the solution as a whole for F108 than for F88. This
may suggest many F88 polymers stay in the form of unimers rather than forming aggregation
(micelle) compared with the F108 case. The microstructure change due to varying the molecular
weight of the type B Pluronics micellar solutions is illustrated in Figure 4.4.1- 2.
The hydration results found here can be essential to deepen the current understanding of phase
behavior of block copolymers. Yardimci et al."
7
mapped out the phase diagram for Pluronics F68
and F 108, which have the same PO/EO ratio. They found the liquid-like packing phase of micelles
99
in between the disordered unimer phase and a micelle phase with crystalline order. Interestingly,
the range of the liquid-like micelle phase in the phase diagram strongly depends on the chain length
of the copolymers. Their results indicate the stabilization of the micelles in liquid phase against
crystalline phase for polymer with shorter chain length, i.e. F68. The liquid-like packing of
spherical micelles discovered in F68, F88, and F108 solutions is also observed very often in block
copolymer melts in a wide temperature-concentration window between a disordered phase, where
the blocks are fully mixed, and an order crystal phase.11-
20
Similar chain-length-dependent phase
behavior is observed in highly asymmetric block copolymer melts. Wang et al.121 showed that the
liquid-like spherical micelle phase of the block copolymer melt is a result of strong and localized
composition fluctuations in the disordered phase based on self-consistent-field theory. They also
predicted the decrease of the temperature range of liquid-like micelle phase when increasing the
chain length, a similar result as what found by Yardimci et al.117 Our current hydration study for
F88 and F108 indicates higher hydration levels in both core and corona regions for the shorter
chain length polymer F88. Wang et al.122 , 2 3 investigated the effect of hydration water on short
time (sub-picosecond) collective vibrations in protein lysozyme. They found that the presence of
hydration water can introduce fluctuations and reduce the energy barrier. In addition, increasing
hydration degree produces phonon population enhancement and therefore increases the fluctuation
amplitude. Roh et aL. 2 4 studied the variation of mean-squared atomic displacement <r2> with the
protein hydration level. They concluded that <r2> increases with the degree of hydration of the
protein molecule in long time (nanosecond) scale. These studies demonstrate that invasive solvent
molecules can promote fluctuations in the macromolecules in both short and long time scales. As
a result, the current hydration study verifies that at fixed PO/EO ratio, type B Pluronics with a
shorter chain length exhibits higher fluctuations introduced by the higher hydration level inside
100
the micelles. These fluctuations can stabilize the liquid phase against crystallization and enlarge
the range of liquid-like micelle phase in the phase diagram according to Yardimci et al.117 and
Wang et al.121 Our finding of hydration is therefore essential for future theoretical work aiming to
take account of the presence solvent molecules, which was not included in previous selfconsistent-field theory.1 2 1
101
10
10
(a)
(b)
F108 0.05 g/ml 60'C
F88 0.05 g/ml 60"C
1041
10'
G
'e
10
1021
10'i
101
C
10"
.r
10 1i
C
l Os
c
100% D20
O
>
D20
80% D20
70% D20
H
>
90%
0
Q0 10
100% D('
90% D20
80% DO
S70%
D20
3
10
-
'U
Q(A'
j*4
Q (A-l)a
10=
(C)
Fs 0.O&g/mI 60"C
0.05g/ml 60'C
0.035
-
7.0x10e-
(d)
6.0x10-
-
5.0110
-
-FlOt
-
0.030
"V
0.025
-
4.Ol
3.SfI0
a
-
o.4
O
"
F
-
2.0x 10'
0.020
-
-
8
/0%
D 20
-
"
"
F88
70% D 20
-
F08 80. D 2 0
F108 0% D2 0
-
-
F8 polymer
-
1108 polymer
-
-=F10890%/ D20
188 90%/ D20
"
0.015
-
eI4 100%/ D20 FI08 100% D20
.0
0.010
-
-
0.0
r (A)
0
20
40
60
80
100
120
140
160
0
20
40
60
10
100
120
140
160
r (A)
r (A)
Figure 4.4.1- 1 The SANS experimental data and the corresponding model fitting curves for 0.05 g/ml micellar
solutions of (a) F88 and (b) F108 Pluronics copolymers at 60 C in 100% D 20 (magenta open right-triangle), 90%
D 20 (olive open diamond), 80% D 20 (blue open up-triangle), and 70% D 20 (red open circle). The fitting curves are
denoted by black lines. The error bars of the experimental data represent one standard deviation and are smaller than
the symbols. The experimental and fitting intensities are subtracted by a constant incoherent background and shifted
on the y-axis for the sake of clarity. (c) The neutron scattering length density (SLD) profile of the F88 (dotted line)
and F108 (solid line) micelles pmicee(r) with the same colors as described in (a) and (b). The orange lines are SLD
profile of polymeric component ppolymer(r). r represents the distance to the micelle center. (d) The radial water number
density distribution H(r) determined from equation (4.3.1.6) for F88 (red line) and F108 (blue line). The inset shows
the accumulated number of water distribution within the sphere with radius r.
102
Water
Molecule
*
PPO Block
PEO Block
0'
Inc'rease
Molecular Weight
Figure 4.4.1- 2 Illustration of microstructure change of type B Pluronics micellar solutions when increasing molecular
weight.
4.4.2 Effect of Temperature
Figure 4.4.2- 1(a) and (b) show the SANS data measured at different temperatures and their
corresponding fitting curves for 0.05 g/ml F88 and F108, respectively, in pure D 20. The fitting
parameters are listed in Table 4.4- 1. Ri, increases when temperature is increased. Rout has similar
trend at low temperature. This is due to the increase of aggregation number Ngg with temperature,
which was also found in type A Pluronics in previous study."'
As a result, the micelle number
density decreases as heating. Figure 4.4.2- 1(c) and (d) demonstrate the number density
distribution of hydrated water of the F88 and F108 micelles. We divide the radial distance r by
core radius Rin in order to normalize the hydration change due to the variation of particle size
contributed by temperature and molecular weight. Both F88 and F108 exhibit the dehydration of
the micelles when increasing temperature. It is well known that PEO is hydrophilic at low
temperature but becomes hydrophobic at high temperature while PPO is always hydrophobic. 96 ""11
The change of hydrophobicity of PEO is due to the weakening of the hydrogen bond between
103
water molecules and the oxide group. The results validate this effect by indicating that fewer water
molecules are bound in both core and shell when temperature is increased. The total number of
water molecules per Pluronic chain, Hota,/Rp/Nagg, also decreases with temperature (except for 70
C) for both F88 and F108 (see Table 4.4- 2). The dehydration effect is more clearly seen for F88
which has smaller molecular weight (Figure 4.4.2- 1(c) and (d)). During dehydration, the outer
layer of water molecules beside the polymeric component will be driven away first and then the
inner layer ones. As mentioned above, fewer water molecules can diffuse inside the F108 micelles
due to the longer distance. At the same temperature, F88 will have more outer layer water than
F 108 and therefore the hydration will change more significantly in F88 (lower molecular weight)
case. The microstructure change due to varying the temperature of Pluronics micellar solutions is
illustrated in Figure 4.4.2- 2.
104
lur
10
10
E
104
10'
10'
10=
10'
.a
10,
0
10
c
10
-
C
1"
10-2
F88 0.05g/mI W0C
10-
---
10"'
L M88
0.O5g/mi
FI08 O.O5g/mI WC
1:108 O.O.V/ml 70 C
F108 O.O5g/nil W0C
i.
<
F108 0.05g/uIl 500C
F1OO.Vgml 4("C
Ia
50"C
Iu:
10"2
10 =
10"'
102
Q(AW)
)
Q(A
0.035-
0.030
0.030
-
-
0.035-
0.025
-
C
4b
0.025-
4'
Q
0.015-
I.a
0.020 -
au
2
O
w
.
I0.010
-
0.010
,
0.020
-
y=
I
rC
0
0.005
:.000
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
.rIrin
0.0
4.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
r/Rin
r/Rin
Figure 4.4.2- 1 The SANS experimental data and the corresponding model fitting curves for 0.05 g/ml micellar
solutions in 100% D 20 of (a) F88 and (b) F108 Pluronics copolymers at temperature 80 C (orange down up-triangle),
70 C (magenta open right-triangle), 60 C (olive open diamond), 50 C (blue open up-triangle), and 40 C (red open
circle). The fitting curves are denoted by black lines. The error bars of the experimental data represent one standard
deviation and are smaller than the symbols. The experimental and fitting intensities are subtracted by a constant
incoherent background and shifted on the y-axis for the sake of clarity. The extracted water number density distribution
H(r/Rn) for (c) F88 and (d) F 108. The inset is the enlargement of H(r/Ri,) within the micellar core. The colors shown
in (c) are the same as described in (a) and that in (d) are the same as described in (b).
105
*
Water
Molecule
PPO Block
;"
r
AJ r-
PEO Block
Increase
Temperature
"--
Figure 4.4.2- 2 Illustration of microstructure change of Pluronics micellar solutions when increasing temperature.
4.4.3 Effect of Concentration
Figure 4.4.3- 1(a) demonstrates the SANS data and corresponding fitting curves for F 108 micellar
solutions at 80 0C at concentrations of 0.01 g/ml, 0.05 g/ml, and 0.18 g/ml. The parameters of
SANS model fitting are listed in Table 4.4- 1. The inter-particle structure factor S(Q) plotted in
Figure 4.4.3- 1(b) indicates that the primary peak of S(Q) becomes sharper and its position shifts
to higher
Q when
increasing concentration. This illustrates the micelle particles arrange into more
ordered structure and the inter-particle distance is shorter in concentrated sample. The decrease of
hard sphere radius R and increase of volume fraction qp with concentration (see Table 4.4- 1) also
verify the shifting and sharpening of S(Q) primary peak. Rin remains almost constant for all the
three concentrations. Rout increases from 83
A to 94 A
as concentration increases from 0.01 g/ml
to 0.05 g/ml due to the large aggregation number Nagg in high concentration. However, Rout does
not change much as further enhancing the concentration from 0.05 g/ml to 0.18 g/ml even though
both Nagg and hard sphere R become much smaller. In addition, the unexpected large volume
fraction (p = 0.48) found in F108 at 0.18 g/ml at 80 0C suggests that the micelles may be in a
106
different state than the 0.01 g/ml and 0.05 g/ml cases. Rheological measurements1
07
by Mohan et
al. on F 108 aqueous solutions in a broad concentration-temperature window indicated that 0.18
g/ml F 108 at 80 C may be in a soft solid phase, which is a possible mixing of randomly oriented
crystallites, micellar fluid, and polycrystalline phase. SANS experiments carried out by Yardimci
et al."
7
suggests that 0.18 g/ml F108 at 80 C is close to the phase boundary between ordered
crystalline micelle phase and liquid-like micelle. The appearing of the second order peak shown
in Figure 4.4.3- 1(a) can demonstrate the crystalline nature of this solution. The extracted water
number density versus normalized radial distance r/Rin is shown in Figure 4.4.3- 1(c). H(r/Rin)
indicates that the degree of hydration grows in the outer part of the coronas (r/Ri, > 1.5) but the
micelle cores (r/Rin < 1) dehydrate significantly when increasing micelle concentration. It was
found that Pluronics F127 (PO/EO ratio = 0.325 and molecular weight = 12600 g/mole) forms gel
state because the micelles pack into partly ordered cubic phases as a result of desolvation of micelle
cores."
0
The change of hydration distribution from 0.05 g/ml to 0.18 g/ml found here confirmed
quantitatively that the formation of crystalline ordered micelle phase accompanies dehydration of
micelle cores. The water molecules driven away from the cores move to the corona region. As a
result, the total number of water molecules per chain
(Htotal,Rp/Nagg)
is comparable in 0.05 g/ml
and 0.18 g/ml F108 at 80 C.
The change of the concentration mainly affects the "diffusiveness" of the solvent-micelle interface,
i.e., am decreases with the concentration. This effect can also be found in Figure 4.4.3- 1(d), which
depicts the SLD distribution of polymer component in the micelles. The micelles of 0.05 and 0.18
g/ml samples have a more defined solvent-micelle boundary while micelles in 0.01 g/ml sample
only show smooth transition across the boundary. For the liquid-like micelle phase, i.e. 0.01 g/ml
and 0.05 g/ml at 80 0C, increasing concentration leads to growth of micelle size by increasing Nagg.
107
The more concentrated slightly hydrophilic PEO chains in the coronas at 80 C in 0.05 g/ml F108
solutions facilitate the attachment of water molecules by providing more sites for the formation of
hydrogen bonds. On the other hand, the dense hydrophobic PPO chains prohibit the further
diffusion of water molecules into the cores. These effects can explain the difference of H(r/Rin)
profile between 0.01 g/ml and 0.05 g/ml F108 solutions.
The microstructure change of the type B Pluronics micellar solutions with the copolymer
concentration is illustrated in Figure 4.4.3- 2.
108
3.0
104
(b)
(a a)
2.5
10'
-
F108 80*C 0.01 g/ml
-F108
80*C 0.05 g/ml
F108 80C 0.18 g/mI
-
2.0
10'
1.5-
C
u
10-
C
1.0
-
10
0.5-
10x2
-.
10'
FIN 0.Olg/mISO"C
0.0..
0.00
0.02
Q (A-)
-
0.06
0.08
0.11
Q (A')
'
0.035
0.04
(d)
I
(c)
0.030
4:10'7
0.025
k< 3x10-7
.a-
9
0.020
2
0.015
I
g
awl
Y
a
I
0.010
Z'
7
I
i
!
V
0.005.
110'7~
an7s-;
x
I
13
29
2.!
)1
!3
_
Oka
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
3
4
r/Rin
5
r/Rin
Figure 4.4.3- 1 (a) The SANS experimental data and the corresponding model fitting curves for F108 micellar
solutions in 100% D2 0 at 80 *C with concentration of 0.18 g/ml (olive open diamond), 0.05 g/ml (blue open uptriangle), and 0.01 g/ml (red open circle). The fitting curves are denoted by black lines. The error bars of the
experimental data represent one standard deviation and are smaller than the symbols. The experimental and fitting
intensities are subtracted by a constant incoherent background and shifted on the y-axis for the sake of clarity. (b)
Inter-particle structure factor S(Q). (c) The extracted water number density distribution H(r/Rin). The inset is the
enlargement of H(r/R,,) in shell region. (d) The extract polymeric SLD distribution ppolymer(r). The colors shown in (c),
(d) are the same as described in (b).
109
Water
Molecule
PPO Block
.PEO
Increase
Concentration
.
--
Block
Figure 4.4.3- 2 Illustration of microstructure change of type B Pluronics micellar solutions when increasing
concentration of the copolymers.
4.4.4 Effect of Hydrophobic/Hydrophilic (PO/EO) Ratio
Figure 4.4.4- 1(a) shows the SANS data and the corresponding fitting curves for 0.01 g/ml L64
and P84 and 0.05 g/ml L64 and F108 all at 40 "C. Figure 4.4.4- 1(b) demonstrates the extracted
water number density versus R/Rin. The fitting parameters can be found in Table 4.4- 1. The water
content in the micellar cores of 0.05 g/ml L64 and 0.01 g/ml P84 solutions at 40 C collapses into
zero because the water number density is too low to be resolved by the current data. The calculated
number density became slightly negative, which is unphysical, and the author set it to be zero. The
failure to accurately determine the hydration profile in the micelle cores of L64 and P84 is also
due to the missing of clear core-shell features in the SANS data (see Figure 4.4.4- 1(a)), i.e. the
bumps at high
Q region
as found in F88 and F108 cases (see Figure 4.4.4- 1(a),(b), Figure 4.4.2-
1(a),(b), and Figure 4.4.3- 1(a)). It is noteworthy that the micelles formed by L64 and P84
Pluronics (type A) have sharp core-shell interface, suggested by the fact that the parameter cc
always collapsed onto the fitting lowest bound (0.01) set by the author (see Table 4.4- 1). In
110
contrast, F88 and F108 (type B) form micelles with smooth interface. This must be due to the
strength of the repulsion interaction between hydrophobic (PPO) and hydrophilic (PEO) blocks.
For type A Pluronics (L64 and P84), the number of EO and the number of PO are comparable (see
Table 4.2- 1) and the repulsive interaction is large; for type B Pluronics (F88 and F108), the
composition of the hydrophilic element (PEO) is much higher than that of the hydrophobic element
(PPO) and the repulsion diminishes. The stronger repulsion in type A Pluronics makes the PPO
and PEO blocks less compatible and sharpens the core-shell interface. In addition, the large
percentage of hydrophilic part in type B Pluronics allows much water to diffuse inside the micelles
as compared with type A Pluronics (see curves of 0.05 g/ml L64 and F108 solutions at 40 0C in
Figure 4.4.4- 1(b)). The water molecules inside the micelles can smear the core-shell interface. It
should be noted that F 108 has much higher molecular weight than L64 but it still has much higher
water number density within the micelles at the same solution conditions (0.05 g/ml and 40 C).
By comparing L64 0.01 g/ml solution with 0.05 g/ml solution at 40 C (Figure 4.4.4- 1(b)), the
water content in the micelles is higher in lower concentration case. This is consistent with type B
results (Figure 4.4.3- 1(c)). However, the much higher water content in L64 0.01 g/ml than in 0.05
g/ml at 40 *C is out of the expectation. Chen et al.1 1 1 investigated the phase diagram of L64 micellar
solutions. Their results indicate that L64 solution at 0.01 g/ml at 40 0C is only slightly above the
critical micellization temperature (CMT). Therefore, the micelles formed in this condition is less
established and therefore more water molecules can diffuse inside. It may even be a mixture of
monomer state and liquid-like micelle state.
Finally, micelles formed by P84 has less water content than those formed by L64 both at 0.01 g/ml
at 40 0C. P84 and L64 have comparable PO/EO ratio but P84 has higher molecular weight. This is
111
consistent with the type B result (see Figure 4.4.1- 1(d)) that the longer traveling distance induced
by the longer polymer chains inhibits the diffusion of water into the micelles.
The
microstructure
change
of the
Pluronics
micellar
solutions
(hydrophobicity/hydrophilicity character) is illustrated in Figure 4.4.4- 2.
112
with
PO/EO
ratio
10
,
104-
10'
100
0
10-I,
F108 0.05g/m 400C
10"
o
L64 0.05g/mi 40"C
A
L64 0.01 g/mI 40"C
P84 0.01g/mI 40'C
o
10
102
Q(-)
(b)
0.035.
0.0300.025
.,r
0.0200.015
0
0.010
a
+
0.005
.
0.000
0.0
0.5
1.0
1.5
2.0
2.5
F108 0.05g/mI 40*C
L64 0.05g/mI 40"C
L64 0.01g/ml 40"C
P84 0.01 ml40"C
3.0
3.5
4.0
r/Rin
Figure 4.4.4- 1 (a) The SANS experimental data and the corresponding model fitting curves for micellar solutions in
100% D 2 0 at 40 C for F108 0.05 g/ml (magenta open right-triangle), L64 0.05 g/ml (olive open diamond), L64 0.01
g/ml (blue open up-triangle), and P84 0.01 g/ml (red open circle). The fitting curves are denoted by black lines. The
error bars of the experimental data represent one standard deviation and are smaller than the symbols. The
experimental and fitting intensities are subtracted by a constant incoherent background and shifted on the y-axis for
the sake of clarity. (b) The extracted water number density distribution H(r/Ri,). The colors shown in (b) is the same
as described in (a).
113
~4.
0
Xa~
Water
Molecule
PPO Block
Low PO/EO Ratio
PEO Block
High Molecular Weight
High PO/EO Ratio
Low Molecular Weight
Figure 4.4.4- 2 Illustration of microstructure change of Pluronics micellar solutions when varying PO/EO ratio
(hydrophobicity/hydrophilicity character).
114
Chapter 5
Summary and Future Work
5.1 Summary
In this study, I have demonstrated that although calcium-silicate-hydrate
(C-S-H) gels,
magnesium-silicate-hydrate (M-S-H) gels, and Pluronics micellar solutions are seemingly very
different systems, they can all be viewed as disordered colloidal systems, which have basic
building particles packing themselves into larger length-scale structure. The information of
microstructure of the disordered colloidal systems can provide essential link to their macroscopic
properties. I have established structure-property relationships for C-S-H gels, M-S-H gels, and
Pluronics micellars solutions. These relationships are usually missing in the literature.
The study can be divided into two main parts: cement binders, which include C-S-H and M-S-H
gels, and micellar solutions.
5.1.1 Cement binders
The study of cement binders can be summarized by Figure 5.1.1- 1. I first contribute to the smallangle scattering (SAS) methodology by building an elaborate analytical model for form factor of
C-S-H basic particles, i.e. globules. This model was applied to SAS data analysis and the essential
structural parameters were successfully extracted. I studied the effects of (1) water content, 3 (2)
115
additives of comb-shaped polycarboxylic ethers (PCEs), 4 (3) methylhydroxyethyl cellulose
additive,5 and (4) Ca/Si ratios on the microstructure of C-S-H gels.
It has been found by the author that C-S-H gel forms globules with larger interlayer spacing at
high water content (WC) because water layer thickness is larger. In addition, the average number
of layers of the globules increases with the WC so the size of the globules grows significantly.
These growing-size globules are much more polydisperse than the globules in the low WC case.
The large globules in the high WC gel then pack into an open fractal structure compared with the
microstructure found in the low WC case. 3 The open fractal structure found in high WC case
demonstrates its poor mechanical property.
For C-S-H gels in the presence of PCE additives, the additives with loose side chains have higher
degree of adsorption on the cement surface and therefore have higher impact on the C-S-H
microstructure. The additives only stay on the surface of globules and do not affect the thickness
of the both water layer and calcium silicate layer. Moreover, PCE additives have the ability to bind
more disk together and therefore the C-S-H globules have larger average number of layers in the
presence of additives. Due to the dispersion force introduced by PCE, C-S-H gels with additives
form more open microstructure.4 This open structure delivers flowability to the cements.
Adding methylhydroxyethyl cellulose (culminal) significantly decreases the size of the globules
by diminishing the disk radius. Thus, the microstructure of C-S-H gels changes from a continuous
structure without culminal to a discrete colloidal structure in the presence of culminal. Also, the
fractal structure becomes slightly open if culminal is added. The small globules and the open fractal
structure found in the C-S-H gel with culminal enhance the mobility of the globules and these
effects facilitate the extrusion process. 5 The combined effects of open microstructure and small
size globules introduced by adding culminal facilitate the extrusion process of cements.
116
Increasing the Ca/Si ratio decreases the size of the C-S-H globules by significantly decreasing the
disk radius although the average number of layers increases a little bit. Also, the fractal structure
becomes more open at high Ca/Si ratio. The continuous structure found in SAS analysis at low
Ca/Si ratio can be also found in scanning electron microscope (SEM) images. The compact
structures found in both nanometer and micrometer length-scales explain the better mechanical
properties for C-S-H gel with low Ca/Si ratio. 5
Recently, a strong attention has been focused on hydraulic binders based on highly reactive
periclase (MgO). This oxide reacts with water and a silica source, forming an amorphous solid
phase (i.e. magnesium-silicate-hydrate: (MgO)X-SiO2-(H2O)y abbreviated as M-S-H 6 0) responsible
for the structural arrest of the hydrated matrix ("setting" of cement). MgO-based cements have
been called "green cements" because little C02 is generated during their production process
compared with their counterparts of CaO-based cements (Ordinary cements). However, the poor
properties of MgO-based cements 63,64 greatly limit their widescale use. To give insight for future
design of robust and eco-friendly binders, the author applied SAS analysis to the M-S-H gel in
order to understand its microstructure. 5 The results show that M-S-H gel also forms fractal
structure. However, the basic building particles of M-S-H gels have very different structure than
that of the C-S-H gels. It was found that the primary unit at the nanoscale level of C-S-H to be a
multilayer disk-like globule, whereas for M-S-H it is a spherical globule. The distinct difference
in the nanoscale structure also reflects in the structure in the micrometer length-scale observed in
SEM. The SEM images show that in the submicron to micrometer length-scale, C-S-H gel forms
foil-like structure while M-S-H forms structure packed by spherical particles. Moreover, the
globules pack into fractal structure with much longer fractal range in the C-S-H case. Since the
disk-like globules and foil-like structure in C-S-H gel interact through "surface contact" while the
117
spherical globules and particles in M-S-H gel interact through "point contact", M-S-H gel
possesses much weaker mechanical properties. The longer fractal range in C-S-H also
demonstrates its stronger binding force. The knowledge of the microstructure of M-S-H is essential
for future design of the eco-friendly binders based on MgO.
Water:
J
O-
O
Nao
"
HP
- large interlayer distance
large number of layers
- more polydisperse
- open structure 4 weak mechanical properties
- McDonald' s model (low WC) Jennings' model (high WC)
- open structure
delivers flowability
CH 3
OH
O
C-S-H
1,OH
CH3
4M-S-H:
1I0
HOC
,H2
MHEC:
-
- open structure
- small globules jFacilitate Extrusion
- McDonald' s model 4 Jennings' model
4
point contact
- Surface Contact
- Decrease mechanical strength
Figure 5.1.1- 1 Summary of structure-property relationships of cement binders studied.
5.1.2 Pluronics Micellar Solutions
The study of Pluronics micellar solutions can be summarized by Figure 5.1.2- 1. Pluronics is a
type of triblock copolymers with a central polypropylene oxide (PPO) block and two polyethylene
118
oxide (PEO) blocks, each on either side of PPO block. It has attracted lots of interests recently
because of its immense industrial applications in drug delivery, biotechnology, detergency, tissue
engineering, food protection, coating and painting. When dissolved into water, Pluronics
copolymers aggregate to form core-shell micelles with the core region composed of hydrophobic
PPO and with the corona region composed of hydrophilic PEO. The phase diagram and
microstructure of various Pluronics have been extensively studied by other researchers. However,
the role of water molecules on the complicated phase behaviors and structures is missing. In this
study, the author used SANS contrast variation method to extract the hydration water distribution
within the micelles. Effects of (1) molecular weight, (2) temperature, (3) concentration, and (4)
hydrophobicity/hydrophilicity character (PO/EO ratio) were investigated by the author. This study
can deepen the current understanding on the phase behavior of amphiphilic copolymers.
It was found that at fixed hydrophobicity/hydrophilicity character (PO/EO ratio), smaller
molecular weight Pluronic has higher degree of hydration and both of the core and corona regions
have higher water number density. It is suggested here that higher water content boosts larger
composition fluctuation, which stabilizes the liquid-like micelle phase from crystallization. This
can explain the larger region of liquid-like micelle phase in the phase diagram of Pluronics with
shorter chain length found by Yardimci et al." 7
Upon heating, the hydration content in both core and corona regions decreases. This verifies that
hydrogen bonds are weakened as increasing temperature and therefore the hydrophilicity of PEO
blocks decreases.
For Pluronics at low PO/EO ratio, increasing concentration dehydrates the core region but the
hydration degree becomes higher in the corona region. This is due to the higher aggregation
number of the micelles at larger concentration. The more PEO chains in the corona in high
119
concentration case provide more sites for water molecules to form hydrogen bonds. In contrast,
the denser hydrophobic PPO chains in the core region prevent water to further diffuse into the
cores.
In general, the current study suggests that lowering water content can drive the phase transition
from liquid-like micelle phase to crystalline micelle phase for low PO/EO ratio.
Studying
the
hydration
distribution
of
Pluronics
at
different
PO/EO
ratio
(hydrophobicity/hydrophilicity ratio) shows that micelles formed by Pluronics at lower PO/EO
ratio have higher degree of hydration even though the Pluronics has much larger molecular weight.
We found in this study the structure-phase behavior relationships for the Plurnoics micellar
solutions. It is suggested that water plays an important role in the phase transition, which was
neglected in previous studies.
120
High MW
Molecular Weight:
- low MW: highhy dration degree
- may explain MW dependent phase diagram
Low MW
*"
40
Temperature:
- high temperature:
low hydration degree
4
.
Dehydration of core may induce
ordered micelle crystalline phase
Concentration:
- high concentration:
* low hydration degree (core)
* high hydration degree (corona)
Figure 5.1.2- 1 Summary of structure-phase behavior relationships of micellar solutions studied.
5.2 Future Work
5.2.1 Cement binders
Firstly, this thesis emphasizes on the microstructure of "mature cement binders". However, the
methodology developed here can be used to study the microstructure change during the hydration
process once the globules of C-S-H or M-S-H start to form. In other words, one can study time121
dependence of the microstructure (aging effect). By combining with rheology measurements, one
can find out how the strength of C-S-H and M-S-H gels develops with their microstructures.
Secondly, the author studied the microstructure of cement binders using static measurement, i.e.
small-angle scattering. We can get supplementary microstructure information through the dynamic
measurement such as quasielastic neutron scattering (QENS). We can study the dynamics of water
as a function of hydration level, say 8%, 15%, and 30%, in both hydrated C-S-H and M-S-H gels
at a temperature range, say 180K-300K, by QENS. Once the microstructure falls in the realm of
continuous Jennings' Colloidal Model II (CM-II), which can be checked by SAS analysis, we can
explain the dynamics results accordingly. According to CM-II, the microstructure of C-S-H can
be schematically described through a hierarchy of pore sizes. The basic structural unit is a disklike globule with a layered internal structure. The water inside the globule is located in both interlamellar spaces and in very small cavities (intraglobular pores, IGP) of dimensions
1 nm. The
packing of these globules produces a porous structure with two characteristic pore types: small gel
pores (SGP) of dimensions 1-3 nm and large gel pores (LGP) of dimensions 3-12 nm. Here we
expect that M-S-H also forms similar hierarchical pore structure. However, due to the difference
in the shape of basic units between the M-S-H and C-S-H gels, their pore structures should also be
very different. Moreover, the absence the layered sub-structure within the M-S-H globules allows
us to get rid of contribution of the water dynamics from the water confined in the layered structure.
Varying water content will significantly affect the water dynamics in the gels. At hydration level
of 8%, only inter-lamellar and IGP water are present. Therefore, only C-S-H gel will have dynamic
signal within the QENS resolution. At hydration level of 15%, the hydration water occupies the
surface of SGP and starts to fill the SGP. At the higher hydration level of 30%, we expect all the
SGPs are filled with water and the surface of LGP starts to be occupied. Moreover, the interaction
122
between water and confining surface will become stronger when decreasing the hydration level.
We know that 40% hydrated white cement shows a fragile-to-strong dynamic crossover. It will be
interesting to know how the dynamics of water and the fragile-to-strong dynamic crossover
phenomenon will change with the hydration level and the pore structure of the studied gels.
Moreover, we can gain extra information of pore structure from the water dynamic,
complementary to the globule structure obtained from SAS.
Finally, to produce a robust but eco-friendly cement binders, one route is to improve the
compatibility between the C-S-H and M-S-H gels in the mixture. This can be achieved by adding
additives to enhance the interaction between the two gels. The microstructure of the mixture gel
in the presence of additives can be studied by SAS. The compatibility and interaction between CS-H and M-S-H gels can be deduced from the data analysis.
5.2.2 Pluronics Micellar Solutions
The picture of the role of water suggested by this work needs a further confirmation from
simulation and modified mean-field theory. Both water influence on the composition fluctuation
and how fluctuation affects the phase behavior need to be clarified by complementary theories.
On the other hand, this work can be used to improve the current mean-field theory which was only
used for block copolymer melt and didn't take account of water contribution.
123
Appendix A
A List of Publications
1. Wei-Shan Chiang, Kao-Hsiang Liu, Christopher Elliot Bertrand, Yun Liu, Sow-Hsin
Chen*, "Water Distribution within the Micelles Formed by Pluronics: Effects of
Temperature, Concentration, Molecular Weight, and PEO/PPO Ratio", manuscript in
preparation.
2. Wei-Shan Chiang, Giovanni Ferraro, Emiliano Fratini, Francesca Ridi, Yi-Qi Yeh, U-Ser
Jeng, Piero Baglioni*, and Sow-Hsin Chen*, "Multiscale Structure of Calcium- and
Magnesium-Silicate-Hydrate Gels", J. Mater. Chem. A., 2, 12991, 2014.
3. Zhe Wang, Wei-Shan Chiang, Peisi Le, Emiliano Fratini, Mingda Li, Ahmet Alatas, Piero
Baglioni, and Sow-Hsin Chen*, "One Role of Hydration Water in Proteins: Key to the
"Softening" of Short Time Intraprotein Collective Vibrations of a Specific Length Scale",
Soft Matter., 10, 4298, 2014.
4. Zhe Wang, Kao-Hsiang Liu, Peisi Le, Mingda Li, Wei-Shan Chiang, Juscelino Leao,
Madhusudan Tyagi, John R.D. Copley, Andrey Podlesnyak, Alexander I. Kolesnikov,
Chung-Yuan Mou, and Sow-Hsin Chen*, "The Boson Peak in Supercooled Water
Confined in Nanoporous Silica Matrix: a Neutron Scattering Study", accepted by Phys.
Rev. Lett., 112, 237802, 2014.
124
5. Christopher Elliot Bertrand, Wei-Shan Chiang, Madhusudan Tyagi, and Sow-Hsin Chen*,
"Low-Temperature Water Dynamics in an Aqueous Methanol Solution", J. Chem. Phys.,
139, 014505, 2013.
6. Wei-Shan Chiang, Emiliano Fratini, Francesca Ridi, Sung-Hwan Lim, Yi-Qi Yeh, Piero
Baglioni, Sung-Min Choi, U-Ser Jeng, and Sow-Hsin Chen*, "Microstructural Changes of
Globules in Calcium-Silicate-Hydrate Gels with and without Additives Determined by
Small-Angle Neutron and X-ray Scattering", J. ColloidInterface Sci., 398, 67, 2013.
7. Zhe Wang, Christopher Elliot Bertrand, Wei-Shan Chiang, Emiliano Fratini, Piero
Baglioni, Ahmet Alatas, Esen Ercan Alp, and Sow-Hsin Chen*, "Inelastic X-ray Scattering
Studies of the Short-Time Collective Vibrational Motions in Hydrated Lysozyme Powders
and Their Possible Relation to Enzymatic Function", J. Phys. Chem. B, 117, 1186, 2013.
8. Hua Li, Emiliano Fratini, Wei-Shan Chiang, Piero Baglioni, Eugene Mamontov, and
Sow-Hsin Chen*, "Dynamic Behavior of Hydration Water in Calcium-Silicate-Hydrate
Gel: A Quasielastic Neutron Scattering Spectroscopy Investigation", Phys. Rev. E, 86,
061505, 2012.
9. Wei-Shan Chiang, Emiliano Fratini, Piero Baglioni, Dazhi Liu, and Sow-Hsin Chen*,
"Microstructure Determination of Calcium-Silicate-Hydrate Globules by Small-Angle
Neutron Scattering", J. Phys. Chem. C, 116, 5055, 2012.
10. Hua Li, Wei-Shan Chiang, Emiliano Fratini, Francesca Ridi, Francesco Bausi, Piero
Baglioni, Madhu Tyagi, and Sow-Hsin Chen*, "Dynamic Crossover in Hydration Water
of Curing Cement Paste: the Effect of Superplasticizer", J. Phys.: Condens. Matter, 24,
064108, 2012.
125
11. Cheng-Si Tsao, Mingda Li, Yang Zhang, Juscelino B. Leao, Wei-Shan Chiang, Tsui-Yun
Chung, Yi-Ren Tzeng, Ming-Sheng Yu, and Sow-Hsin Chen*, "Probing the Room
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