Thursday, April 10, 2014
4:00 pm
Spalding Laboratory 106 (Hartley Memorial Seminar Room)

Chemical Engineering Seminar

Organizing colloids in space and time: from viscoelastic nonequilibrium states to the directed assembly of reconfigurable conducting materials
Kenneth S. Schweizer, G. Ronald and Margaret H. Morris Professor of Materials Science and Engineering, Materials Science and Engineering, University of Illinois at Urbana-Champaign

Dense suspensions and mixtures of colloids and nanoparticles of various shapes and tunable interactions find diverse applications in materials science and engineering.  We have developed a microscopic statistical mechanical theory for the intermittent activated dynamics of hard and soft, spherical and nonspherical, and repulsive and sticky, colloids under quiescent and strongly deformed conditions.  Predictions for how steric caging, physical bond formation, particle softness and shape anisotropy compete leading to new types of nonequilibrium phase diagrams, slow relaxation, kinetic gelation and vitrification, and elastic properties will be described and comparisons with experiments presented.  The approach has also been extended to dense mixtures of spheres and rods which are of interest as functional inks for direct write printing applications and in multiple biophysical contexts. I will also discuss our very recent attempt to use equilibrium statistical mechanics to design quenched disordered templates composed of large mesh rigid rod gels to direct in a fast, triggerable and reversible manner the assembly and metal-insulator transition of colloids for energy applications.  Design rules to achieve remarkably sharp structural transitions with increasing colloid-gel and/or colloid-colloid attractions have been formulated based on two mechanisms:  template driven wetting of the percolated rod network, and large fluctuation mediated aggregation associated with avoided phase separation in porous media.  Dramatic implications for hopping electrical conductivity will be discussed.

Contact Martha Hepworth martha@cheme.caltech.edu
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