Characterization of Nanoparticle Composites and Fabrication of Ordered Structures Katherine Best, Hyun Suk Kim, P.K. Sudeep, Caroline Miesch, Todd Emrick, James Watkins, Alfred J. Crosby

NSF CMMI-0531171

Polymer Poster SymposiumCenter for Hierarchical Manufacturing ● University of Massachusetts Amherst

Xu, et al. PRL. 96 (2006) 066104. Cai, et al. J.Am.Chem.Soc. 130 (2008) 6076. Huang, et al. Nat Mater. 4 (2005) 896.

“Coffee Ring Effect” Maragoni Instabilities Dewetting

Manufacturing Nanoparticle/Polymer Assemblies

The directed placement of

nanoscale objects presents

significant challenges

Objective: Develop robust, line-

based processing methods that can

be used to assemble and distribute

chemically-tailored nanoscale

particles

m

nm

q

• Line assemblies with

controlled spacing and

dimensions demonstrated

• Ability to be directly

integrated into polymer

matrix confirmed

• Chemistry and processing

developments for better

control within assembly

20 mm

(a) Fluorescence micrographs of stripe patterns of CdSe nanoparticles

(4 nm in diameter)

(b) Gradient stripe patterns of CdSe NPs (6 nm in diameter)

(c)–(f ) Optical micrographs of stripe patterns of Au NPs

(3 nm in diameter) with different spacing distances.

100 5000

100

500

(m

m)

p (mm)

h

w 0 100 500

200

300

400

500

5

10

15

20

25 height

h (

nm

)

p (mm)

width

w (m

m)

x : moving distance of the substrate

min : minimum spacing

qc : critical contact angle

when depinning occurs

s : stopping time

min (dh/dw)

pinnning, if q > qc

depinning, if q < qc

min s0.43 for 1mg/mL toluene

s0.38 for 1mg/mL chlorobenzene

s0.77 for 4mg/mL toluene

q0 = q+ qd ~ q + (dh/dw) (dh/dw)

x = min & q0 - qc min, at q = qc

q = q0 - q H/(L + x) x (x << L)

0.01 0.1 11

10

100 1 mg/mL Chlorobenzene

1 mg/mL Toluene

4 mg/mL Toluene

0.77

m

inmm)

s (s)

0.43

0.38

Capillary force holds the solution between a

fixed blade and a moving substrate

Frictional drag is exerted on the solution as blade

moves over substrate

Flow coating is a easy and versatile tool to

generate constant or gradient in polymer film

thickness from nm to mm

* **

Stripe pattern

by stick-slip motion

Casting film

by friction drag

Convective

deposition

Withdrawal velocity,

υ= 1 μm/s

υ= 2 μm/s

υ= 5 μm/s

Flow coating Programmed Flow-coating for Line Assemblies Controlled Formation of Nanoparticle Line Assemblies

Characterization of PMMA Line Assemblies Prediction of Minimum Spacing Limit

Objective : Dynamic self-assembly of nanoparticles or/and polymers via flow-coating

Use flow coating to translate from laboratory scale films to roll-

to-roll processing of films

- Maintain block copolymer alignment observed in Pluronic PEO-PPO-PEO triblock

copolymer blends

Tirumala et al., Chem. Mater. 2007, 19, 5868

AFM images of neat Pluronic F127 (a)

and blends with PAA 16.67wt% (b) and 28.5wt% (c)

Gravure coating Roll coating

Ordered Block Copolymers via Flow Coating

1500 30000

20

40

60

80

100Bound vs Unbound Ligand Tg

Tg

(oC)

Ligand MW (g/mol)

PS ligand

Au-PS Np

CdSe-PS Np

Core

material

Target core size

(nm)

Core size from

TEM (nm)

Core size from

Uv-vis

absorption*

(nm)

Ligand length

(g/mol)

MW ligand

from GPC

(g/mol)

wt%

organic

from TGA

CdSe 4-5 44

(λ=580nm)1500

1500

(PDI=1.1)73

CdSe 4-54

(λ=575nm)3000

2990

(PDI=1.3)

Au 4-5 4 - 1500 1500 83

Au 4-5 - 3000 2990 93

Nanoparticles

*Bawendi et. al., J. Am. Chem. Soc, 1993, 115, 8706-15

• Develop a general understanding on how

nanoparticle characteristics impact composite

material properties

- Core composition

- Core size

- Ligand density

- Ligand binding strength

- Ligand length

Objective : Impact of changing nanoparticle characteristics on a matrix

Motivation and Objective

- CdSe Nanoparticles

- Au Nanoparticles

Nanoparticle Synthesis

Entropic Effect

- Low density region of

chain segments

- Decrease in Tg

+

PS-covered NPs PS

PS-CdSe NPs

(4-5 nm)

PS-Au NPs

(~ 4.2 nm)

Summary

• We have demonstrated that flow-coating can be utilized as a simple and

facile strategy to form nanoparticle and polymer stripe patterns.

• We explained the minimum spacing limit by taking into consideration the surface

roughness of deposited PMMA

• Programmed flow-coating provided a robust route to control the spacing between

lines in a constant or gradient way.

Polystyrene/Nanoparticle Composites

• Initial study exploring the effect of functionalized nanoparticle interactions on

glass transition temperature (Tg) and modulus of polystyrene

• Eventually look at nanoparticle behavior under nonlinear deformations of the

composite

• Composite samples – 131K PS/Au-1500PS

– 131K PS/1500PS

• Composite samples– Thicknesses 300-400nm

– 2-3 samples for each condition

0 2 4 6 8 10

96

97

98

99

100

101

102

103

104

105

Nanocomposite Tg

Tg

(C

)

wt% Filler

1500PS / 131KPS

Au-1500PS / 131KPS

0 2 4 6 8 102.0

2.4

2.8

3.2

3.6

4.0

4.4

4.8

5.2

Nanocomposite Moduli

Mod

ulu

s (

GP

a)

wt% Nps or Ligand

1500PS+131K PS

AuNp-1500PS + 131K PS

• Fixing PS ligands to a nanoparticle core has been shown to increase the Tg of the

ligand

Future Work

• Multicomponent line patterning via flow-coating

• Formation of complex pattern by modifying flow-coating process

• Large scale ordered thin films with roll to roll processing

• Integration of assembled structures into a composite material

• Incorporation of nanoparticle/block copolymers composites with film alignment

to create hierarchical assemblies

• Addition of PS functionalized gold nanoparticles appears to impact PS matrix Tg

and modulus the same as the addition of PS chains equal to the ligand molecular weight

Nanoparticle/Polymer composites