Dynamics and Disorder in Colloidal Crystals of
Osmotically Compressed vs
Uncompressed Thermo-responsive Microgel
Particles
B.V.R. Tata
Light Scattering Studies Section
Condensed Matter Physics Division
Indira Gandhi Centre for Atomic Research,
Kalpakkam – 603 102
tata@igcar.gov.in
Collaborators:
Ms. J. Brijitta, RA
Mr. R.G. Joshi, Scientific Officer
Mr. Deepak Kumar Gupta, Scientific Officer
Optics-11: 23-25/5/2011
Research Theme
Nanoparticle
dispersions
Photonic
Crystals
Polymer
hydrogel
Portable photonic
crystals

Synthesis & Characterization
Structure, Dynamics and Phase transitions
in colloids, gels and composites
(colloids as super atoms, mimic atomic systems)
Photonic crystals through colloidal route
Rheology
Menu
Introduction: Nanoparticle dispersions
Effect of Temperature
•Crystal to Liquid Transition
•Dynamics across melting
[Violation of Dynamical criterion]
SLS/ DLS
Effect of Osmotic Pressure
Tunability of Bragg Diffraction
[ Particle size and SPD reduces]
Second type Disorder
Stacking Disorder
UV visible & Confocal
Nanoparticle Dispersions
Hard Sphere
 > 0. 5
PMMA
SPD 11%
Fluid-solid Transition
Charged
Stimuli-responsive
 ~ 0. 005
PS or Si, CPD < 26%
Gas-liquid
Gas-Solid,
Liquid to Solid,
BCC to FCC
Can not vary Size and SPD
Temperature is not a convenient parameter
 > 0. 74
PNIPAM
Size and SPD
are tunable by
varying T, P
Effect of Size (Charge) Polydispersity
“Ordering Phase Transitions in Charged Colloids”(VCH Publishers. NY. 1996)
Eds. Arora & Tata.
CPD: 26% = ESPD: 17%
Tata & Arora
J. Phys: Condens. Matter, 3, 7983 (1991)
J. Phys. Condens . Matter, 4, 7699, (1991)
J. Phys. Condens. Matter, 7, 3817 (1995)
Size Polydispersity in
PNIPAM nano/microgel
system is tunable by T, P ?
Spin-glass like?
Synthesis of PNIPAM nanogel particles
Brijitta, Tata & Kaliyappan, J. Nanosci. Nanotechnol. 9, 5323 (2009)
Dilute(non-interacting samples)
139mM
1.96mM
1.05mM
2.22mM
300
260
Purification:
VPT occur at T ~ 34 C
240
220
200
180
160
140
120
Dialysis
Concentrate
Ion-exchange
(Mixed bed)
273 nm
T Decreasing
T Increasing
280
Diameter (nm)
Reagents:
N-isopropylacrylamide (NIPAM)
Methylene bisacrylamide (BIS)
Sodium dodecylsulphate (SDS)
Potassium persulphate (KPS)
Synthesis at 70C
100
20
25
30
35
40
45
50
55
o
T C
273
SPD (%) Effective
Charge
density
 (C/cm2)
0.39
5.5
0.25
4
353
6
0.22
520
5
0.19
Mean Dia
(dh nm)
25oC
520 nm
238
60
Phase Behavior of 273nm PNIPAM Nanogel dispersions
Brijitta, Tata & Kaliyappan, J. Nanosci. Nanotechnol. 9, 5323 (2009)
7.1 x 1013 cm-3
Crystalline
4.36 x 1012 cm-3
Liquid-like
1.06 x 1014 cm-3
Glass-like
6
5
60
4
Is(q) (arb. units)
3
I(q)(10 arb.units)
Is(q)
7
3
2
1
0
-1
20
0
1
1.0
1.5
2.0
5
-1
2.5
3.0
q(10 cm )
Fluid – Fluid Transition
at 31.5oC
40
Melting (Crystal to
Liquid) at 26oC
Fluid – Fluid Transition
at 30.5oC
2
3
q (105 cm-1)
Meting of PNIPAM Nanogel Crystals
273 nm
C
C
Imax(arb. units)
4  q111 
np 


3 3  2 
1000
400
3
300
πd
  h np
6
L
3
Imax(q) (arb. units)
3000
2000
238 nm
300
250
200
150
50
200
L
100
23
24
25
o
T( C)
100
22
24
26
Melting transition:
T( C)
o
28
26.2 oC
 = 0.76 (at 25
= 0.71 (at melting)
oC)
Compressed
Melting transition: 24 .2oC
 = 0.47 (at 25 oC)
= 0.48 (at melting)
Uncompressed
Dynamics Across Melting
Dynamical Criterion for freezing of colloidal liquids
DL/ Ds ~ 0.1
DL: Long-time Self Diffusion coeff.
Ds= Short time Self Diffusion coeff.
D0= Free Diffusion coeff.
DsD0 ( at low )
238 nm,  = 0.47
273 nm,  = 0.76
0.10
0.10
0.08
0.08
L
DL / DS
L
DL/D S
0.06
0.04
0.02
0.00
24
0.04
0.00
26
0
T ( C)
DL/Ds = 0.02 < 0.1
C
0.02
0.02
C
0.07
0.06
28
23
24
25
o
T( C)
DL/Ds = 0.07 < 0.1
26
Shear melted Colloidal crystal of charged polystyrene spheres
 = 0.003, d =0.100 nm
0.12
L
Methodology is RIGHT
NO experimental Artifacts
0.09
D L/D S
0.08
0.04
C
0.00
15
30
45
t (min)
60
75
Why DL/Ds is low ?
Interpenetration of polymer chains of PNIPAM at
the surface: DL to be low
Self-Healing Colloidal Crystals
Ashlee St. John Iyer and L. Andrew Lyon,
Angew, Chem. Int. Ed., 48, 4562 (2009)
Tunabilty of Bragg wavelength
by Osmotic pressure
Uncompressed state: B
Compressed state:
B
np
np & d
Effect of Pressure
Lietor-Santos et al,
Macromolecules, 42, 6225, (2009)
Hydrostatic
pressure
Self-Healing Colloidal Crystals
Ashlee St. John Iyer and L. Andrew Lyon, Angew, Chem. Int. Ed., 48, 4562 (2009)
The dopant particle (d ~ 1850 nm) is experiencing
compression because of the osmotic pressure of the highly
concentrated microgel environment ( d ~ 715nm)
•External osmotic pressure Pext ~104 Pa.
•Elastic modulus of swollen microgels ~ 102–104 Pa
•Osmotically induced deswelling is expected
Effect of osmotic pressure
Schematics of stirred cell ultrafiltration setup
Suspension
Argon Gas
Membrane
Stirred Cell
P1
P2
N
S1
N
S2
S3
P3
P4
N
N
S4
P ~ kPa
UV-Visible spectra of PNIPAM microgel crystals with increase in P
2eff d s sin   n
Extinction (%)
0.4
0.3

0.58
0.63
0.65
0.73
0.2
0.77
0.81
0.89
1.01
0.1
4  2eff 


np 
3 3  B 
3  B 
d nn  
2  2eff 
np 
0.0
700
800
 (nm)
1.2
2
d nn 3
2
1.00

1.0
0.9
2
0.75
3
4
13
-3
np ( 10 cm )
Equation of state
(HS Colloidal crystals)
z  6
 (dh)
1.1
900
 3  a z  b 
P  n p k BT 


 1  z   z  c  
1.25
dnn/dh
(dnn)
dnn/dh
P
For fcc structure
a = 0.62, b = 0.71, c = 0.59
0.50
Blue shift of B

P(Pa)
0.58
0.63
1.3
2.0
0.65
0.73
2.7
25.4
0.74
0.74
2702.9
2862.2
0.74
3127.8
0.74
3528.37
dnn/dh > 1
np

d = dh
dnn/dh < 1
np

d < dh
dnn
P
 = 0.74 (constant)
Osmotic compression leads to deswelling of particles for   0.74
Disorder in PNIPAM Microgel Crystals:
CLSM Study
Type of disorder
( arising due to T, SPD, and stacking)
Types of Crystal Imperfections (Disorder)
First type
Second type
Finite Size effects
Thermal motion of
particles
Strain –induced
lattice deformations
Abrupt loss of positional
order at the boundary
Preserves long-range
Correlations in particle
positions
Positional correlation
length reduces
Reduces
intensities of
the higher-order peaks in
the diffraction pattern via
the Debye-Waller factor
No change in peak width
Peak width increases
with increase in length
of the diffraction wave
vector
Dullens & Petukhov, EPL, 77, 58003 (2007)
Peak width is
independent of
diffraction wavevector
 Sample S1 ( np = 2.75×1013cm-3, = 1.81 )
dh=501 nm SPD = 37%
 Sample S2 ( np = 4.75×1013cm-3, = 3.13 )
8
Experimental,
c
dnn= 0.372 m
g(r)
4
For S1, dnn=372 nm
For S2, dnn=292 nm
Observation
dnn < d
0
8
Ideal hexagonal Lattice
4
0
0.0
0.5
1.0
1.5
2.0
r (m)
6
Experimental ,
4
d
dnn= 0.292 m
g(r)
2
0
6
Ideal hexagonal Lattice
4
2
0
0.0
0.5
1.0
r (m)
1.5
Particles shrunk from 501 nm to 372 nm and 292 nm respectively upon
osmotic compression
Ordering
Reduction in SPD
2.0
Characterize type of disorder : By determining structure factor S(q):
 Calculated radial profiles of S(q) in [10] direction: By averaging S(q) over
Oand radius q.
2
short arcs with
an
of
2
Nopening angle



1
N = Total number of particles
S (q ) 
exp(iq.r )

N
n
rn as
= position
vector
of particles
 Width of peaks (FWHM) analyzed
a funct. of
diffraction
order
n 1
Sample S1,
S(q)
100
(c)
10
1
0.1
0
1
2
3
4
q/q
5
6
7
10
Sample S2,
S(q)
100
(d)
10
1
0.1
0
1
2
3
4
5
6
7
q/q10
Higher order diffraction peaks are more broadened and lesser in
intensity
 For ideal HCP lattice
(simulated): Peak width
independent of diffraction order
 Presence of second type
disorder in S1, S2 and
arises due to SPD
15
,
,
0.3
S1
S2
Ideal hexagonal lattice
12
9
0.2
6
0.1
0.0
3
0
1
2
3
4
5
6
Diffraction Order, q/q10
Area under diffraction peaks decrease as a function of
diffraction order indicating the presence of first type disorder
Area under the Peaks
 Increase is more for S1 (SPD ~
11%) than S2( SPD ~7).
0.4
Relative Peak width
q/q10
 Peak width increases
monotonically with increase in
diffraction order:
CLSM Results on large size particles:
DLS on Dilute sample at 23oC dh= 834nm, SPD =17%
1.00
Uncompressed
Compressed
488nm
P(d)
0.75
T= 23oC
0.50
825nm
0.25
SPD=13%
SPD=5%
0.00
0.2
0.4
0.6
0.8
1.0
1.2
d (m)
CLSM measurements provide clear evidence: Osmotic compression of
PNIPAM particles to a volume fraction ≥ 0.74 not only influences particle
size but also SPD
DLS measurements
1200
1.0
1000
0.8
900
0.6
800
0.4
700
SPD
Diameter (nm)
1100
0.2
600
0.0
20 22 24 26 28 30 32 34 36 38 40
o
T ( C)
SPD also decreases with increase in T
Why the distribution changes upon variation of P or T ?
Diameter d = 520nm, volume fraction =0.44
I. As-prepared
Shear melt
8 mm
25 mm
Suspension
CLSM study
Cover glass
• RHCP
II . Re- crystallized
Heat up to 40C
(Isotropic liquid)
Slow cooling
(0.15C/min)
• FCC
stacking prob.  = 0.42 0.15 (RHCP) ;
0.95 0.17 (FCC)
Origin of split-second peak :
Second neighbours or from B-planes
1.2
Ex
2.4 pt.
Volume fraction =0.43, np =5.841012 cm-3
g(r)
3.2
0.8
0.4
1.4
1.6
1.6
1.8
r/d
Lattice constants a = 620 nm ~1.2d
c =1012nm ~1.95d
c/a=1.63
g(r)
0.8
0.0
3.2
hcp
2.4
1.6
0.8
0.0
x
0
1
2
r/d
A
B
y
r/d=1.54
r/d=1.68
A
More than 50 % B-planes moved (shear) in y-direction by 0.68d
3
4
Why RHCP & FCC?
The sudden withdrawal of shear on the shear melted liquid
leads to solidification into RHCP structure in the case of the asprepared sample
B-plan shift: Arise due to local shear stress locked up during
the freezing of the shear melted liquid.
Slow cooling rate of 0.15oC/min might be responsible for the
occurrence of fcc structure in the recrystallized sample.
Conclusions
PNIPAM Nano/microgel dispersions differ from Hard-sphere/Charged
colloidal dispersions both in dynamics and phase behaviour
Role of Inhomogeneties with in each gel particle needs to understood
to explain the narrowing of Size distribution upon osmotic compression
Sabareesh, Sidhartha Jena and Tata, Bussei Kenkyuu 87, 88 (2006);
AIP 832, p. 307 (2006)