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 T c ) –Dynamics (Viscosity, chain diffusion) –Glass transition temperature T g –Instabilities and pattern formation Ordered Disordered

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/CO 2 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 nm Thin film Polymer coil R g ~2-20 nm

Self Organization of chains on a surface determined by film thickness, temperature, substrate topography h1h1 h2h2 h3h3 L Effects 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) C 60 fullerenes (“buckyballs”) and -(iii) mica-type layered silicate inorganic clays on the T g of thin polymer films in the nanometer thickness range nm Polymer coil R g ~2-20 nm from mmptdpublic.jsc.nasa.gov/jscnano /

The Glass transition of Polymer thin film nanocomposites C 60, and carbon nanotubes have a similar effect PS:  =9 Nanocomposite:  =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

Dynamic processes in confined environments Neutron scattering experiments Relaxation processes affect scattering intensity as well as change d /dt Phase Separation Glass Transition Temperature (K) Reduced Intensity

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)