DOCTORIAL DISSERTATION
LINDSAY BOMBALSKI
Thesis Title: Growth and Effect of Polymeric Ligands on Colloidal Particles
and Tailoring the Optical Properties of Particle Additives
Carnegie Mellon University
Department of Chemistry
Copyright Lindsay Bombalski 2007
All Rights Reserved
Preface: Organic/Inorganic composite materials, even those composed of materials in the
nanoscale range (ie. nanocomposites), face the challenge of opacity caused by light
scattering of particle inclusions. Recent advances in synthetic polymer chemistry and the
understanding of the physical properties of nano-sized materials provide the means to
address this long-standing problem. This work demonstrates that effective medium
concepts in conjunction with novel controlled radical polymerization techniques can be
applied to design particle filler materials with reduced or even diminished light
scattering. Advances in synthetic techniques involving inorganic particle materials allows
for the preparation of well-defined, characterizable core-shell hybrids of a precisely
calculated core and polymer composition. Controlled radical polymerization (CRP),
specifically Atom Transfer Radical Polymerization (ATRP), has expanded the
availability and purity of these neat materials, and is therefore, the preferred method for
the synthesis of our model materials. Standard light scattering methodology is evaluated
in detail for these progressive materials with available mathematical methods, proving the
effective medium theory (EMT) concept. A comparison of the experimental data to
simulated form factor expressions is presented to evaluate the appropriate modelgeometry to analyze static light scattering of polymer-coated particle systems. The
findings of the research open the door to a better understanding for core-shell models and
novel transparent organic/inorganic composite materials.
Thesis Committee Members: Dr. Michael R. Bockstaller, Prof. Richard D. McCullough,
Dr. Newell Washburn, and Prof. Toby M. Chapman.
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Acknowledgements: To my entire thesis committee, thank you for all of your help and
suggestions. May your willingness to proceed through difficulties be exponentially
rewarded. To my parents and family who gave me all the love, support, and
encouragement that allowed me to follow even the hardest problems with confidence.
Without you none of this would be possible, and therefore all of my work is your work.
To Dr. Michael Bockstaller, whose incredible patience, methodical strength, and modesty
has allowed me continue my perseverance for great science. To all the members of the
Matyjaszewski group that throughout the years have given me an incredible background,
direction, and great scientific conservations. And to Kevin, who has loved me through all
of it.
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PREFACE
ACKNOWLEDGEMENTS
TABLE OF CONTENTS
LIST OF FIGURES
LIST OF SCHEMES
LIST OF TABLES
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TABLE OF CONTENTS
CHAPTER 1. INTRODUCTION AND APPROACH
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1.1 INTRODUCTION
1. 2 THEORETICAL BACKGROUND
1.2.1. Refractive Index and Scattering Theory
1.2.2 Effective Medium Theory
CHAPTER 2. MATERIALS
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2. 1 SYNTHETIC INTRODUCTION
2.1.1 Uncontrolled/Free Radical Polymerization
2.1.2 Controlled Radical Polymerization
2.1.3 Specific ATRP Techniques & Limitations of Normal ATRP in Colloidal
Systems
2.2 SYSTEMS
2.2.1 DILUTION SYSTEM ACHIEVEMENT: Polyacrylonitrile-Silica Composites as
Templates for Nanoporous Carbons
2.2.2 Experimental Detail for Polyacrylonitrile-Silica Composites
2.2.2 MINIEMULSION SYSTEMS ACHIEVEMENTS
2.2.2.1 AGET ATRP of Poly(n-butyl acrylate)-Silica Composites
2.2.2.2 Experimental Detail for Poly(n-BA)-Silica Miniemulsion Systems
2.2.2.3 AGET ATRP of Poly(n-butyl acrylate)-Quantum Dot Composites
2.2.2.4 Experimental Detail for Quantum Dot Miniemulsion Systems
2.3 ARGET ATRP FOR COMPOSITE SYNTHESIS
2.3.1 ARGET ATRP method description
2.3.2 Experimental Detail for Quasi-Transparent Polystyrene-Silica Composites
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CHAPTER 3. METHOD BACKGROUND
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3.1 LIGHT SCATTERING
3.1.1 Static Light Scattering
3.1.1.1 Rayleigh Scattering
3.1.1.2 Form Factor
3.2.1.3 Structure Factor
3.2.2 Dynamic Light Scattering
3.2.2.1 Autocorrelation Function and Relaxation Time Spectra
3.2.2.2 The Diffusion Coefficient
3.2 PRACTICAL CONSIDERATIONS
CHAPTER 4. CHARACTERIZATION AND EXPERIMENTAL RESULTS 78
4.1 SYNOPSIS
4.2 CHARACTERIZATION OF PHYSICAL PROPERTIES
4.2.1 Molecular weight and grafting density
4.2.2 Transmission Electron Microscopy
4.2.3 Dynamic Light Scattering
4.3 CHARACTERIZATION OF OPTICAL PROPERTIES
4.3.1 Refractive Index Increment
4.3.2 Static Light Scattering
4.4 FURTHER ANALYSIS AND DISCUSSION
4.4.1 Characterization of Angular Dependence
4.4.2 Interaction of Particles in Solution
CHAPTER 5: CONCLUSIONS AND SUGGESTIONS FOR FUTURE STUDIES
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5.1 CONCLUSION
5.2 FUTURE STUDIES
CHAPTER 6. BIBLIOGRAPHY
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APPENDIX A: SUPPLEMENTAL INFORMATION
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LIST OF FIGURES
Chapter 1
Figure 1.1. Bending of light caused by changes in refractive index at the interface of two
materials. Velocity of the beams slows at it moves into a medium with a higher refractive
index (n2 in this case), reducing the angle of refraction, relative to the incident angle, at
the interface. The relationship is described by Snell’s law: n1sinθ1 = n2sinθ2.
Figure 1.2. Illustration of the effective medium theory. Properties of the individual
constituents (such as conductivity, and dielectric constant) of a composite for which the
volume of each is known can be mathematically combined in order to approximate values
for entire medium.
Figure 1.3. Illustration of the concept of transparent nanocomposites. Scattering is
produced by differences (left) in dielectric constants of the matrix (m) and the particle
(p) and are absent when the dielectric constants of the medium and particle match (right).
Figure 1.4. Conceptualization of the effective medium theory. For an incident beam, the
effective dielectric constant (εeff) of a non-magnetic material (μ = 0) is a function of the
dielectric constants of both the particle (εp) and the matrix (εm). Likewise in the case of
hybrids, the dielectric constant of the polymer graft(s) (εg) contributes to the εeff for the
composites material. Maxwell-Garnett theory predicts the theoretical compositions from
the effective permittivity and vice versa.
Figure 1.5. Calculated effective refractive index neff of a silica-core/PS-shell composite
nanoparticle (see equation 1.4). For the composition m(PS)/m(silica) ~ 0.2 the core-shell
particle is isorefractive with toluene (black dotted line). The refractive index of silica and
PS are assumed to be nSiO2 = 1.458 and nPS = 1.550.
Chapter 2
Figure 2.1: X-Ray diffraction diffractograms of three nanocomposite samples. The peak
from the suspension-prepared clay composites (a) indicates the presence of aggregates.
Figure 2.2. Diagram illustrating the necessity of control over growth of a polymer chain
in colloidal system. Randomness of free radical processes lead to inefficient initiation,
and particle instability.
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Figure 2.3. (A) The first-order kinetic plot of ATRP of BA from silica MIs in bulk. Inset:
the first-order kinetic plots during the first 6 hours. (B) Evolution of molecular weight of
polyBA of hybrid particles versus monomer conversion and (C) GPC traces of polyBA
from bulk ATRP of BA from silica particle MIs. Polymerization conditions: Table 2.2,
entry 1-5.
Figure 2.4. Thermogravimetric analysis of SiO2 initiator and SiO2-g-PAN in N2 or air
atmosphere: a) hybrid-1; b) hybrid-2.
Figure 2.5. TEM images of nanoporous carbon prepared from hybrid-1: a) thin film; b)
sublayer film.
Figure 2.6. TEM images of nanoporous carbon prepared from hybrid-2: a) thin film; b)
thick film.
Figure 2.7. a) Nitrogen adsorption isotherms and b) pore side distribution of thick film of
nanoporous carbon prepared from hybrid-2.
Figure 2.8. (A) The first-order kinetic plots for AGET ATRP of BA from silica particle
MIs in miniemulsion. (B) Evolution of molecular weight of polyBA of hybrid particles
versus monomer conversion and (C) GPC traces of polyBA from ATRP of BA from
silica particle MIs in miniemulsion. Polymerization conditions: Table 2.2, entries 6-9.
Figure 2.9. Tapping mode AFM micrographs of core-shell hybrid particles from SR&NI
ATRP (a) and AGET ATRP (b) in miniemulsion.
Figure 2.10. FTIR spectra of THP and THP-Cl.
Figure 2.11: Visible absorption spectra of the samples: a) CdS-TOPO, b) CdS-Py, c)
CdS-THP-Cl, and d) CdS-THP-Cl/Pn-BA. Samples a) and b) were recorded in toluene; c)
and d) in THF. The corresponding solvents were used as references.
Figure 2.12. Tapping mode AFM phase micrograph (2.5x2.5µm) of core-shell hybrid
CdS-THP-Cl/ Pn-BA nanocomposite prepared by AGET ATRP in miniemulsion.
Figure 2.13: GPC trace of Pn-BA prepared by AGET ATRP after detachment from CdSTHP-Cl nanoparticles.
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Chapter 3
Figure 3.1. Light Scattering experimental setup (a) and definitions for Incident (Io) and
scattered (Is) beam intensities, detector distance (rd), and angle of measurement (θ). The
representations for scattering vector (q) and angle (θ /2) and wave vectors (ki and ks) are
given in b. Composite factors of importance (utilized mainly in the structure factor
calculations), namely particle radius (R), inner/core radius (Ri), radius of gyration (Rh)
and particle to particle distance (ri-rj), are defined in (c).
Figure 3.2: Graph of the form factor P(qR) for a sphere, given in equation 3.8.
Calculations utilized λ = 532 nm, np = 1.55, and R = 10 nm. For angles less than 15° the
value of P(qR) is very close to 1.
Chapter 4
Figure 4.1. Illustration of the optical characteristics of PS@SiO2 core-shell particle
system. The dotted gray line indicates the dielectric constant of the embedding medium
toluene.
Figure 4.2a. Size exclusion chromatography traces of polystyrene chains after detachment
from core-shell samples, measured against polystyrene standards. From left : DP10
(black), DP140 (red), DP150 (blue), and DP760 (green).
Figure 4.2. Panels b-e depict bright-field electron micrographs of the respective particle
samples prepared in Table 4.1. Panel b: DP10 (grafting density σ = 0.71 chains/nm2).
Panel c: DP140 (grafting density σ = 0.09 chains/nm2). Panel d: DP150 (grafting density
σ = 0.5 chains/nm2). Panel e: DP760 (grafting density σ = 0.5 chains/nm2). Scale bar is
100 nm.
Figure 4.3. Computer-extrapolated (via CONTIN) relaxation time spectra from sample
angles of overlaid with the corresponding correlation functions given in Figure 4.7. a)
DP150 at 150 degrees b) DP10 at 30 degrees c)DP10 at 150 degrees d) Correlation
functions and resulting relaxation times (returned by CONTIN analysis) for bare silica,
DP10, and DP150 at 30 degrees.
Figure 4.4. Calculated D vs. q for all angles, and average D shown with lines of similar
color. DP10 display contrary results to TEM in relation to size. Particle diameters derived
from this data were 56.21 nm for DP150 and 127.67 nm for DP10.
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Figure 4.5. Field autocorrelation function g1(q, t) at q = 2.75  107 m-1 of particle
samples DP150 (left) and DP760 (right) with the fits to stretched exponential function
(Kohlrausch-Williams-Watts). Stretching parameter is  = 0.97 and 0.99 for DP150(a)
and DP760(b), respectively, indicating single-dispersed particles of uniform size in
solution. The hydrodynamic radius follows from Stokes–Einstein relation as rH, DP150 = 19
nm and rH, DP760 = 35 nm, respectively. For particle samples DP10 and DP140 the
scattering intensity was too small to facilitate resolution of the correlation functions
without dust interference (See Figure 4.6).
Figure 4.6. Sample correlation functions for various samples. The break in the curve
observed in DP140 is attributed to sudden interference from dust.
Figure 4.7. Refractive Index Increment measurement for sample DP10.
Figure 4.8. Refractive Index Increment measurement for sample DP760.
Figure 4.9. The refractive index increment for particle samples DP10, DP150, and
DP760 confirming that index-matching (i.e. (dn/dc) = 0) is expected for particle
compositions m(PS)/m(SiO2) ≈ 0.2, close to the theoretical value.
Figure 4.10. Scattering intensity I(q) vs. q of PS-coated Silica DP10(red), 150 (blue), &
760 (black, except toluene) for all measured concentrations. Note that equal mass
concentration of all particle samples implies an even stronger scattering contribution per
particle for DP760 since its number concentration is only about one third of DP150.
Figure 4.11. Intensity (q) vs. q of PS-coated Silica DP10 at various concentrations.
Figure 4.12. Intensity (q) vs. q of PS-coated Silica DP150 at various concentrations.
Figure 4.13. Intensity (q) vs. q of PS-coated Silica DP760 at various concentrations.
Figure 4.14. Intensity (q) vs. q of PS-coated Silica DP140 at various concentrations.
Measurement taken at a 50% filter setting.
Figure 4.15. Intensity (q) vs. q of PS-coated Silica DP140 and DP150. Measurement
taken at a 10% filter setting.
Figure 4.16. Absolute values for Intensity (q) vs. q of PS-coated Silica DP10, 140, 150, &
760 for comparable volumes at filter setting of 10% versus toluene standard. Equivalent
volumes were 10.0 (DP10), 0.5(DP150), and 0.3 (DP140) mg/mL, respectively. The
curve of 0.5 mg/mL for DP140 is shown (overlapping) to accentuate minimal scatter in
this sample for higher concentrations.
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Figure 4.17. Total scattered intensity R(q) for particle samples DP10 (diamonds), DP140
(circles) and DP150 (squares) revealing the reduced angular dependence of the scattering
intensity for particle samples DP10 and DP140 indicating a decrease in optical phase
shift.
Figure 4.18. Scattering characteristics of PS@SiO2 particle systems at equal particle
number density c/M. Plot of the total scattering intensity R(q) at q = 9.16  106 m-1 as
function of the particle composition m(PS)/m(SiO2) for all particle samples. The
reduction of forward scattering of sample DP140 confirms the approximate indexmatching condition. Arrow indicates theoretical null-scattering composition
m(PS)/m(SiO2) ≈ 0.19.
Figure 4.19. Digital photograph of equivalent volume density of samples used in this
study dispersed in carbon disulfide in front of a black background. From left: DP10,
DP150, and DP760.
Figure 4.20. Top: Form factor model fits to the raw intensity (I(q))data for the DP150
sample (concentration = 0.97 mg/mL). Effective sphere (left) and core-shell (right) best
fits shown by the blue lines. (Note: Best fits determined via the sum of the RMS residual
errors squared.) Bottom: Error for the above fit for each curve in terms of the residual.
Figure 4.21. Top: Form factor model fits to the raw intensity (I(q))data for the DP150
sample (concentration = 0.97 mg/mL) for the effective sphere after rejecting the first four
data points (left).
Figure 4.22. Top: Core shell form factor model fits to the raw intensity (I(q))data for the
DP150 sample for concentrations 0.3 mg/mL(left) and 0.17 mg/mL (right). Particle radii
determined to be 29.1 and 30.5 nm, respectively. Bottom: Error for the above fit for each
curve in terms of the residual.
Figure 4.23. Best fit curve comparison for Guinier approximation (black) versus effective
sphere (left, red) and core shell (right, red) form factors. Top: Core shell form factor
model fits to calculated (R(q))data for the DP150 sample for concentrations 0.17 mg/mL
(left) and 0.3 mg/mL (right) after rejecting first two points due to a poor background
calibration at those angles). Bottom: Error for the above fit for each curve in terms of the
residual. Guinier approximation error given in black.
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LIST OF SCHEMES
Chapter 1
Scheme 1.1. Synthesis of poly(styrene)-functionalized silica nanoparticles of varying
grafting density and degree of polymerization.
Chapter 2
Scheme 2.1: Initiation, propagation and termination reactions for free radical
polymerization. Rate constants of dissociation (kd), initiation (ki), propagation(kp),
coupling (kct), and disproportionation (kdt) termination as well as reaction components
catalyst/initiator (I), radical (R°), and Monomer(M) are given in shorthand. Monomer and
Polymer(P) are interchangeable.
Scheme 2.2. ATRP. The activation and deactivation steps proceed with the rate constant
kact and kdeact. Generated free radicals (Pn·) propagate and terminate (including
combination and disproportionation) with rate constants kp and kt.
Scheme 2.3. Nanoporous carbon sheets templated from solution-processable PAN-grafted
silica nanoparticle (SiO2-g-PAN) prepared by ATRP.
Scheme 2.4. Illustration of ATRP of BA grafting from silica particles in bulk (left) and
miniemulsion (right).
Scheme 2.5: AGET (A) and Simultaneous Reverse and Normal Initiation (B)
modifications to the general ATRP scheme. In this case, the initiator (I) was
Azobisisobutyronitrile (AIBN) and the reducing agent was ascorbic acid.
Scheme 2.6: Route to ATRP from particle surfaces in miniemulsion system.
Scheme 2.7: Synthetic strategy for the preparation of QDs/polymer nanocomposites by
AGET ATRP in miniemulsion.
Scheme 2.8: Ligands exchange at the surface of the QDs: TOPO= tris(octyl)phosphine
oxide;Py=Pyridine;THP=tris(hydroxypropyl)phosphine;THP-Cl=tris(hydroxypropyl)
phosphine oxide macroinitiator.
Scheme 2.9: ARGET modifications to the general ATRP scheme. In this case, the
reducing agent was Sn(II) (specifically tin(II) 2-ethylhexanoate (Sn(EH)2).
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LIST OF TABLES
Chapter 2
Table 2.1. MWs and MW Distributions of the Polymers from Different Nanocomposites
Table 2.2. ATRP of BA from Functionalized Silica Particles in Bulk and Miniemulsion
Chapter 4
Table 4.1. SiO2-PS samples prepared by ARGET ATRP for transparent target material
and studies.
Table 4.2. PS@SiO2 calculated and measured size agreements.
Chapter 5
Table 5.1. Composition and architecture of selected polymer-coated particle systems for
compatibilization and index-matching with the respective matrix polymer (calculated
using Equation 1.2 and assuming an inorganic particle diameter of d = 20 nm). n denotes
the refractive index. Polymers listed are abbreviated as such: polymethyl methacrylate
(PMMA), polystyrene (PS), acrylonitrile (A), polyvinyl alcohol (PVA), polyacetic acid
(PAA), and polypropylene oxide (PPO).
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