Nanoparticle Assembly: From Fundamentals to ...

Nanoparticle Assembly: From Fundamentals to Applications Faraday Discussion Self-Assembly and Rheology of Colloidal Particles in Hexagonal and Nematic Liquid Crystals .

Siddharth Kulkarni and Prachi Thareja Chemical Engineering, Indian Institute of Technology, Gandhinagar.

Approach and Methodology

Particles in LC: • A new class of soft materials: complexity of the LC matrix with reference to the classical colloidal solutions. • Interparticle interactions governed by the anisotropic LC medium: magnitudes higher than in isotropic medium

Display Screens LCDs

ElectroOptical Devices

Liquid Crystals

Controlled drug delivery

Rheology: Oscillatory Measurements 10

5

10

MBBA

Spherical Silica (dp=400 nm)

TiO2 (21 nm)

+

Elongated FeOOH (l=500 nm)

+

MBBA: weak nematic liquid crystal Methoxybenzilidene Butylaniline

Gp' (Pa)

10

0

FeOOH/H1 (0.5C/min)

104

FeOOH/H1 (1C/min) FeOOH/H1 (2C/min)

3

0

1

2

3

4

SiO2/H1 (1C/min) SiO2/H1 (2C/min) FeOOH/H1 (2C/min)

3

10 0.000

5

0.004

0.008

0.012

0.016

0.020

Volume Fraction, 

wt %

102

8

10

12

14

100 10-1

16

wt%

G'~8.15

Pure Bond Stretching 𝜀=0

3

10

Strong Link Regime

102

102

Pure MBBA 10-2

10-1

100 101 Angular Frequency, (rad/s)

Pure Bond Bending 𝜀=1

x

𝑑𝑓

x

𝑑𝑓

2.03

2.38

1.49

2.69

102

Shih Model

G' ~

(1 2  x )/(3 d f )

𝑑𝑓 : Fractal dimension

Intra-floc links govern the elastic network behaviour.

x: connectivity parameter

103

2.5 wt% 5 wt% 7.5 wt% 10 wt% 12.5 wt% 15 wt% Blank

Shear Thickening

101 0

10

10-1 10-2 100

FeOOH/H1 (1C/min)

at same 

SiO2/H1 (2C/min)

6

103

FeOOH/H1 (0.5C/min)

Difference in Gp'

Gelation: Frequency Independent G'

Rheology: Rotational Measurements

SiO2/H1 (0.5C/min)

SiO2/H1 (1C/min)

4

Volume Fraction, 

10

SiO2/H1(0.5C/min)

2

104

5

104

2.5 wt% 5 wt% 7.5 wt% 10 wt% 12.5 wt% 15 wt%

101

105

Effect of particle loading at different cooling rates

1

2

3

10 10 Shear rate (1/s)

10

System follows HerschelBulkley Model till 10 wt% loading Model Equation: . C

  A  B

102 101 2.5 wt% 5 wt% 7.5 wt% 10 wt% 12.5 wt% 15 wt% Blank

100 10-1 10-2 100

101 102 Shear rate (1/s)

103

Wt%

A

B

C

2.5

0.67

0.173

0.834

5

0.89

0.338

0.778

7.5

2.51

0.346

0.78

10

6.40

0.257

0.848

Conclusions Particles in H1 LC phase• Composite Strength (Gˈ) and microstructure are functions of:  Particle Concentration  Higher concentration, higher Gp’.  Particle Shape  FeOOH particles self-assemble and form a percolating network which imparts higher elasticity to the H1 LC phase than the SiO2 particles.  Cooling rate  Increase in cooling rate leads to more number of small H1 domains, imparting higher elasticity. Particles in Nematic LC• Formation of composites with significantly high solid-like properties at low volume fraction (ϕ