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Physical Society Colloquium
Colin Denniston Johns Hopkins University Interfaces regulate bulk behavior in biological systems and the formation and properties of industrial materials from shampoo to liquid crystals. Complex fluids allow greater control of interfacial phenomena via the extra degrees of freedom associated with their internal structure and composition. The interfacial boundary conditions involve coupled relations between the fluid velocity, the order parameter, and external applied fields. I illustrate this with two examples. In the first, I show how differential wetting of the components of a fluid mixture coupled to a concentration gradient can drive convective flows. I construct a quantitative model of this effect and demonstrate its use in the construction of an entropy driven nano-motor. In the second example I report on a novel method of dynamically controlling the boundary conditions at the surface of a nematic liquid crystal using a surface flexoelectric effect. By moving the surface directors one can manipulate defects that lie near the surface. Understanding of this effect and how defects move in a liquid crystal can be used to create a bistable display that retains its state with no applied voltage.
Thursday, February 21st 2002, 15:00 |