Structure and Dynamics of Soft Condensed Matter

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Liquid crystals, gels and lipid membranes are all examples of soft condensed matter, materials that 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; are formed by self-assembly of smaller components such as particles, polymers or lipid molecules; and 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 to produce both interesting physics and novel applications. Our focus is on the relationship between microscopic structure and macroscopic material properties in several systems. In this proposal, we plan to work in three areas. We will 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 informed design of these materials, which is critical for their application in polymer electrolyte membrane fuel cells. We are also starting studies of nanostructure in polymer films formed from blends of electron-donating polymers and molecular acceptors for application to organic photovoltaic devices. Again, the goal is to understand how the nanostructure is determined to inform design of better materials. A third research area explores the relationship between microstructure and rheology in 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.