Kenneth S. Schweizer

Professor Schweizer received his B.S. degree, summa cum laude, from Drexel University and a Ph.D. in physics from UIUC in 1981. Following a two year postdoctoral appointment at AT&T Bell Labs, he was a senior research scientist at Sandia National Laboratories in the Organic and Electronic Materials Department. Dr. Schweizer joined the UIUC faculty in 1991, and is presently a professor of Materials Science and Engineering, Chemistry, and Chemical Engineering, principal investigator in the interdisciplinary Frederick Seitz Materials Research Laboratory, and the Associate Director of the National Science Foundation Nanoscale Science and Engineering Center for the "Directed Assembly of Nanostructures".

Our interdisciplinary group develops and widely applies new equilibrium and time-dependent microscopic statistical mechanical theories of condensed phase systems. We employ both analytical techniques and computationally intensive methods. The focus is on "soft materials" or "soft condensed matter", such as polymers, colloids, nanoparticle fluids, and crosslinked rubber networks. Such systems are rich in fundamental science and also play critical roles in diverse materials technologies.

Soft materials are notoriously sensitive to external perturbations (e.g. applied stress, electric and magnetic fields), and can exist in diverse equilibrium and nonequilibrium phases including liquids, suspensions, liquid crystals, crystals, elastomeric solids, amorphous glasses, and gels. We also study "hybrid" materials composed of soft and hard building blocks. For example, (i) suspensions of inorganic, metallic or glass particles dissolved in a polymer solution, (ii) dense mixtures of nanoparticles in a rubbery polymer matrix corresponding to a polymer nanocomposite, and (iii) fluids of nano-objects with surface-grafted polymeric moieties which can direct mesoscale self-assembly. All these material systems are characterized by a rich and complex competition between entropy (translational, conformational, packing) and enthalpy each of which can favor either order or disorder. An overarching theme is to build theoretical descriptions at a molecular level which address both the chemically specific and generic physical aspects in a unified and predictive manner. Projects are motivated by and/or coupled to many experimental efforts at Illinois and around the world.

A major theme of our present research is to understand the equilibrium structure, phase transitions and properties of diverse polymeric and colloidal systems. We simultaneously develop dynamical descriptions that can predict when these materials become kinetically arrested. In the polymer area, both the ultra-slow local dynamics in the deeply supercooled liquid regime and the vitrification event, and the amorphous solid or thermoplastic state which is characterized by a time-dependent evolution of structure and properties ("physical aging") that is sensitive to external stress, are under intense study. For colloids and nanoparticles a prime focus is diffusion and flow at very high concentrations and/or in the presence of strong intermolecular attractions which can induce glassy or gel-like behavior. Dynamical fluctuation and heterogeneity effects are studied by combining theory and small scale Brownian simulation. A major new thrust is to generalize our dynamical methods to nanoparticle and colloidal systems composed of nonspherical objects. This is a frontier area which holds the promise of bringing the complexity of molecules and chemistry to the particle science field. New theories that address the role of particle shape on structure and slow dynamics for both relatively compact molecule-like objects (e.g. nanocubes, tetrahedra, triangles) and highly anisotropic shapes such as rods and disks are being constructed and applied. For such "molecular colloids" the possibility of chemical heterogeneity or patchiness is also an exciting new direction which is expected to result in novel condensed phase structural arrangements, dynamics, and material properties.

Hybrid systems composed of spherical or anisotropic colloids and nanoparticles mixed with and/or attached to soft and flexible polymers are of high interest. Questions such as the phase behavior, structural organization over many length scales, and the effect of hard inclusions on polymer dynamics, mechanical properties and kinetic arrest are under investigation. Understanding these complex systems requires an extension and synthesis of concepts from polymer, colloid and surface physics, and a full treatment of the interface between chemically and structurally disparate building blocks.

Other problems of enduring interest include the dynamics of polymers in thin films and between hard surfaces, conjugated and electroactive polymers, the slow dynamics of entangled polymers under quiescent and mechanically driven conditions, the application of concepts from colloid and polymer science to biomolecular systems, and the formation, dynamics and mechanical properties of amorphous metallic glasses.

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