Complex Materials Group

Peter F. Green

Department of Chemical Engineering and Texas Materials Institute

The University of Texas at Austin

• Conventional applications: – Coatings– Membranes – Lubrication

• Processing: – Self assembly– Lithography

• Device technologies– Light emitting diodes– Organic photodiodes– Sensors

Motivation for research : problems at the nanoscale in polymer based systems

thin film transistor

(T. Kawase, et. al. Digest of Technical Papers 2001)

Polymer is the active material

component

Particles of Nanoscale dimensions

h~1-50 nm

Polymer thin films (h~1-100 nm) exhibit properties that differ from the bulk (new phenomena)

• Confinement (entropic), enthalpic (polymer-polymer) interactions and interfacial interactions influence properties

– Surface induced ordering of block copolymers

– phase stability (change in Tc)

– Dynamics (Viscosity, chain diffusion)

– Glass transition temperature Tg

– Instabilities and pattern formation

OrderedDisordered

Topics of Interest: Self-Organization, Dynamics and Wetting

• Polymer-nanoparticle systems (bulk and thin film)

• Glass Transition temperature of thin films

• Chain dynamics and miscibility in confined geometries

• Instabilities in thin films (mixtures and homopolymers)

• Wetting and nano-scale organization of structured liquids

• Polymer thin film/CO2 systems (with Johnston group)

Polymer-based Nanocomposites

• Properties at the nanoscale are of broad interest, cross-cutting many disciplines… diverse technical issues (e- transport and single-molecule transistors to mechanical properties and automobile bumpers)

• Polymer-based nanocomposites: polymers+ nanoscale particles (fullerenes, layered silicates, nanoparticles, nanotubes)-new pathways to “tailor” properties of materials

20-50 nm

Thin film

Polymer coil Rg~2-20 nm

Self Organization of chains on a surface determined by film thickness, temperature, substrate topography

h1

h2h3

LEffects of temperature and film thickness

Patterned Substrates

The Glass transition temperature of nanocomposite thin films

- Background: The glass transition temperature of polymer thin films

Influence of - i) single walled carbon nanotubes, - (ii) C60 fullerenes (“buckyballs”) and - (iii) mica-type layered silicate inorganic clays

on the Tg of thin polymer films in the nanometer thickness range

20-50 nm

Polymer coil Rg~2-20 nm

from mmptdpublic.jsc.nasa.gov/jscnano/

The Glass transition of Polymer thin film nanocomposites

• C60, and carbon nanotubes have a similar effect

85

90

95

100

105

110

115

120

125

0 50 100 150 200 250

h (nm)

PS

PS+1wt% layered silicate clay

PS+5 wt% layered silicate clay

3/1

1)(

h

aThT gg

PS: =9Nanocomposite: =4

Decrease in reflects the increase in fraction of the slowly relaxing domains

The effect of nanoparticles is to increase the effective fraction of slowly relaxing domains in the sample

37

36

35

34

Film

Thi

ckne

ss (

nm)

25020015010050

Temperature (o C)

Dynamic processes in confined environmentsNeutron scattering experiments

Relaxation processes affect scattering intensity as well as change d <u2>/dt

0

0.5

1

1.5

2

2.5

3

0 100 200 300 400 500 600

MS

D (

A2)

Temperature (K)

Phase Separation

Glass Transition

Temperature (K)

Red

uced

Int

ensi

ty

0.25

0.3

0.35

0.4

100 200 300 400 500

Dewetting of Thin Films

• Mechanisms (determined by the nature of the intermolecular interactions)

Nucleation: Heterogeneous and homogeneous

Spinodal Dewetting: Spontaneous amplification of capillary waves

Droplets

film

substrate

Misc. Info about the group

• Current Funding: National Science Foundation (DMR, STC), Robert A. Welch Foundation, Sematech

• Facilities used: Atomic force microscopy, spectroscopic ellipsometry, X-ray Scattering, TEM, neutron scattering, dynamic mechanical analysis, rheology

• Collaborations: Johnston, Ganesan, Sanchez, Yacaman

Loo, Bonnecaze, Korgel

• Distribution of Researchers during last 12 months: 9 PhD Students (2 co-advised), visiting scientist, undergraduates, shared post-doc (Johnston group)