B.V.R. TataLight Scattering Studies Section

Condensed Matter Physics Division

Indira Gandhi Centre for Atomic Research,

Kalpakkam – 603 102

tata@igcar.gov.in

Dynamics and Disorder in Colloidal Crystals of

Osmotically Compressed vs

Uncompressed Thermo-responsive Microgel

Particles

Optics-11: 23-25/5/2011

Collaborators:

Ms. J. Brijitta, RA

Mr. R.G. Joshi, Scientific Officer

Mr. Deepak Kumar Gupta, Scientific Officer

Nanoparticle

dispersions

Polymer

hydrogel

Photonic

Crystals

Portable photonic

crystals

Research Theme

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

Hard Sphere Charged Stimuli-responsive

> 0. 5PMMA

SPD 11%

~ 0. 005PS or Si, CPD < 26%

PNIPAM > 0. 74

Nanoparticle Dispersions

Can not vary Size and SPD

Temperature is not a convenient parameter

Fluid-solid Transition

Gas-liquid

Gas-Solid,

Liquid to Solid,

BCC to FCC

Size and SPD

are tunable by

varying T, P

Effect of Size (Charge) Polydispersity

CPD: 26% = ESPD: 17%

“Ordering Phase Transitions in Charged Colloids”(VCH Publishers. NY. 1996)

Eds. Arora & Tata.

Tata & AroraJ. Phys: Condens. Matter, 3, 7983 (1991)

J. Phys. Condens . Matter, 4, 7699, (1991)

J. Phys. Condens. Matter, 7, 3817 (1995)

Spin-glass like?

Size Polydispersity in

PNIPAM nano/microgel

system is tunable by T, P ?

Synthesis of PNIPAM nanogel particles

Reagents: N-isopropylacrylamide (NIPAM) 139mMMethylene bisacrylamide (BIS) 1.96mMSodium dodecylsulphate (SDS) 1.05mMPotassium persulphate (KPS) 2.22mM

Synthesis at 70C

520 nm273 nm

20 25 30 35 40 45 50 55 60100

120

140

160

180

200

220

240

260

280

300

Dia

mete

r (n

m)

T oC

T Decreasing

T Increasing

VPT occur at T ~ 34 C

Brijitta, Tata & Kaliyappan, J. Nanosci. Nanotechnol. 9, 5323 (2009)

Mean Dia

(dh nm)

25oC

SPD (%) Effective

Charge

density

(C/cm2)

238 5.5 0.39

273 4 0.25

353 6 0.22

520 5 0.19

Purification:Dialysis

Concentrate

Ion-exchange

(Mixed bed)

Dilute(non-interacting samples)

7.1 x 1013 cm-3

Crystalline

1.06 x 1014 cm-3

Glass-like

4.36 x 1012 cm-3

Liquid-like

Phase Behavior of 273nm PNIPAM Nanogel dispersions

Brijitta, Tata & Kaliyappan, J. Nanosci. Nanotechnol. 9, 5323 (2009)

I s(q

)

1.0 1.5 2.0 2.5 3.0-1

0

1

2

3

4

5

6

7

q(105cm

-1)

I(q)(

10

3 a

rb.u

nit

s)

1 2 30

20

40

60

I s(q

) (a

rb

. u

nit

s)

q (105 cm-1)

Fluid – Fluid Transition

at 31.5oC

Melting (Crystal to

Liquid) at 26oC

Fluid – Fluid Transition

at 30.5oC

3

111p

2

q

33

4n

Melting transition: 26.2 oC

= 0.76 (at 25 oC)

= 0.71 (at melting)

p

3

h n6

πd

Meting of PNIPAM Nanogel Crystals

23 24 2550

100

150

200

250

300

I ma

x(q

) (a

rb.

un

its

)

T( oC)

C

L

22 24 26 28100

200

300

400

1000

2000

3000

L

C

I ma

x(a

rb.

un

its)

T( oC)

238 nm273 nm

Melting transition: 24 .2oC

= 0.47 (at 25 oC)

= 0.48 (at melting)

Compressed 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.

DsD0 ( at low )

24 26 280.00

0.02

0.04

0.06

0.08

0.10

0.02

DL/D

S

T (0C)

L

C

23 24 25 260.00

0.02

0.04

0.06

0.08

0.10

0.07

DL /

DS

T(oC)

L

C

273 nm, = 0.76 238 nm, = 0.47

DL/Ds = 0.02 < 0.1 DL/Ds = 0.07 < 0.1

15 30 45 60 750.00

0.04

0.08

0.12

DL/D

S

t (min)

L

C

0.09

Shear melted Colloidal crystal of charged polystyrene spheres

= 0.003, d =0.100 nm

Methodology is RIGHT

NO experimental Artifacts

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 n p

Compressed state: B n p & d

Lietor-Santos et al,

Macromolecules, 42, 6225, (2009)

Hydrostatic

pressure

Effect of Pressure

The dopant particle (d ~ 1850 nm) is experiencing

compression because of the osmotic pressure of the highly

concentrated microgel environment ( d ~ 715nm)

Self-Healing Colloidal Crystals

Ashlee St. John Iyer and L. Andrew Lyon, Angew, Chem. Int. Ed., 48, 4562 (2009)

•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

P ~ kPa

S3 S4S1

P1P2

P3 P4

S2

N N N N

Arg

on

Ga

s

Stirred Cell

Suspension

Membrane

nsindseff 2

UV-Visible spectra of PNIPAM microgel crystals with increase in P

700 800 9000.0

0.1

0.2

0.3

0.4

Ex

tin

cti

on

(%

)

(nm)

0.58

0.63

0.65

0.73

0.77

0.81

0.89

1.01

P

32

22

3

2

33

4

nn

p

eff

Bnn

B

eff

p

dn

d

n

Equation of state

(HS Colloidal crystals)

cz

bza

z1

3TknP Bp

For fcc structure

a = 0.62, b = 0.71, c = 0.59 26z

2 3 40.9

1.0

1.1

1.2

0.50

0.75

1.00

1.25d

nn/d

h

dn

n/d

h

np ( 10

13cm

-3)

(dnn

)

(dh)

Blue shift of B

Osmotic compression leads to deswelling of particles for 0.74

P = 0.74 (constant)

dnn

P(Pa)0.58 1.3

0.63 2.0

0.65 2.7

0.73 25.4

0.74 2702.9

0.74 2862.2

0.74 3127.8

0.74 3528.37

dnn/dh > 1

dnn/dh < 1

np

np

d = dh

d < dh

Disorder in PNIPAM Microgel Crystals:

CLSM Study

Type of disorder

( arising due to T, SPD, and stacking)

Types of Crystal Imperfections (Disorder)

Finite Size effects

Abrupt loss of positional

order at the boundary

Peak width is

independent of

diffraction wavevector

First type

Thermal motion of

particles

Preserves long-range

Correlations in particle

positions

Reduces intensities of

the higher-order peaks in

the diffraction pattern via

the Debye-Waller factor

No change in peak width

Second type

Strain –induced

lattice deformations

Positional correlation

length reduces

Peak width increases

with increase in length

of the diffraction wave

vector

Dullens & Petukhov, EPL, 77, 58003 (2007)

0

4

8

0.0 0.5 1.0 1.5 2.00

4

8

g(r

)

Experimental, c dnn= 0.372 m

r (m)

Ideal hexagonal Lattice

0

2

4

6

0.0 0.5 1.0 1.5 2.00

2

4

6

g(r

)

r (m)

Experimental , ddnn= 0.292 m

Ideal hexagonal Lattice

For S1, dnn=372 nm Observation

For S2, dnn=292 nm dnn < d

Particles shrunk from 501 nm to 372 nm and 292 nm respectively upon

osmotic compression

Ordering Reduction in SPD

Sample S1 ( np = 2.75×1013cm-3, = 1.81 )

Sample S2 ( np = 4.75×1013cm-3, = 3.13 )

dh=501 nm SPD = 37%

N = Total number of particlesrn = position vector of particles

Characterize type of disorder : By determining structure factor S(q):

2

1

).exp(1

)(

N

n

nrqiN

qS

0 1 2 3 4 5 6 70.1

1

10

100

S(q

)

q/q10

Sample S2, (d)

0 1 2 3 4 5 6 70.1

1

10

100

S(q

)

q/q10

Sample S1, (c)

Calculated radial profiles of S(q) in [10] direction: By averaging S(q) over

short arcs with an opening angle of 2Oand radius q.

Width of peaks (FWHM) analyzed as a funct. of diffraction order

Higher order diffraction peaks are more broadened and lesser in

intensity

1 2 3 4 5 60.0

0.1

0.2

0.3

0.4, S1

, S2

Ideal hexagonal lattice

Re

lati

ve

Pe

ak

wid

th

q

/q1

0

Area

un

der t

he P

ea

ks

Diffraction Order, q/q10

0

3

6

9

12

15

Peak width increases

monotonically with increase in

diffraction order:

Increase is more for S1 (SPD ~

11%) than S2( SPD ~7).

For ideal HCP lattice

(simulated): Peak width

independent of diffraction order

Presence of second type

disorder in S1, S2 and

arises due to SPD

Area under diffraction peaks decrease as a function of

diffraction order indicating the presence of first type disorder

CLSM Results on large size particles:DLS on Dilute sample at 23oC dh= 834nm, SPD =17%

0.2 0.4 0.6 0.8 1.0 1.2

0.00

0.25

0.50

0.75

1.00

SPD=5%

Uncompressed

Compressed

P(d

)

d (m)

825nm

488nm

SPD=13%

T= 23oC

CLSM measurements provide clear evidence: Osmotic compression of

PNIPAM particles to a volume fraction ≥ 0.74 not only influences particle

size but also SPD

20 22 24 26 28 30 32 34 36 38 40

600

700

800

900

1000

1100

1200

T (oC)

Dia

mete

r (n

m)

0.0

0.2

0.4

0.6

0.8

1.0

SP

D

SPD also decreases with increase in T

Why the distribution changes upon variation of P or T ?

DLS measurements

Shear melt

Cover glass

Suspension25 mm

8 mm

I. As-prepared

CLSM study• RHCP

II . Re- crystallizedHeat up to 40C

(Isotropic liquid)

Slow cooling

(0.15C/min)

• FCC

Diameter d = 520nm, volume fraction =0.44

stacking prob. = 0.42 0.15 (RHCP) ; 0.95 0.17 (FCC)

Lattice constants a = 620 nm ~1.2d

c =1012nm ~1.95d

c/a=1.63

Volume fraction =0.43, np =5.841012 cm-3

Origin of split-second peak :

Second neighbours or from B-planes

More than 50 % B-planes moved (shear) in y-direction by 0.68d

r/d=1.54

r/d=1.68y

x

A

B

A

0 1 2 3 40.0

0.8

1.6

2.4

3.2

r/d

0.0

0.8

1.6

2.4

3.2

g(r

)

1.4 1.6 1.80.4

0.8

1.2

r/d

g(r

)

Ex

pt.

hcp

The sudden withdrawal of shear on the shear melted liquid

leads to solidification into RHCP structure in the case of the as-

prepared 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.

Why RHCP & FCC?

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)