Structure and dynamics of soft condensed matter

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Liquid crystals, gels, polymers and lipid membranes are all examples of soft condensed matter; these materials are characterized by weak intermolecular interactions, mechanical softness, and a susceptibility to thermal fluctuations.  Many of these materials are either two-dimensional, quasi-two dimensional, or fractal and they exhibit a rich range of behaviour including phase transitions, pattern formation, and non-linear material properties.  They are also of great practical interest - contact lenses are made of polymeric gels, and liquid crystals form the basis for many display screens - and they can be used as models of more complicated biological systems.  This field has the potential both to produce interesting physics and novel applications.      Our focus is the relationship between microscopic structure and macroscopic material properties in several systems. We study the microstructure of polymer films formed from copolymers consisting of hydrophobic and conducting blocks.  The goal of these studies is to achieve fundamental understanding of the relationship between microstructure and conductivity in ionic polymers, leading to more informed design of these materials, critical for their application in polymer electrolyte membrane fuel cells.  A second research area explores the relationship between microstructure and rheology of yield-stress fluids, materials that flow or yield only when a critical stress is applied; everyday examples include mud, shaving foam and mayonnaise.  We study the light scattered by these materials to study diffusion and elasticity at small length scales and to characterize the microstructure of the material.  The goal of these studies is to uncover universal aspects of yield stress behaviour, leading to the development of microscopic theories.  We also study properties of vesicles, spherical shells formed from lipid bilayers that are used in drug delivery systems and as model membranes.  Here we investigate the properties of the extrusion process by which they are made and material properties of lipid bilayers, including the tension at which they rupture.  These studies are of interest to researchers using this technique as well as to physicists interested in the equilibrium shapes and dynamics of lipid systems.