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Session G28 - Dillon Medal Symposium.
MIXED session, Tuesday afternoon, March 19
Room 275, America's Center
The dynamics of concentration fluctuations present in a polymer-polymer-solvent solution near its critical point are examined for both simple shear and extensional flow. It is shown that the system of polystyrene/polybutadiene in dioctyl phthalate can be described by a simple modification to the Cahn-Hilliard model. The result is a dynamical response characterized by a single relaxation time that accurately predicts measurements of flow-induced orientation and distortion of the fluctuations using small angle light scattering and scattering dichroism. Experiments involving the start up and cessation of steady shear flow, and oscillatory flow are described. The single relaxation time scale response is clearly demonstrated using a Cole-Cole representation of the dynamical data acquired in oscillatory shear, where the in-phase and out-of-phase data are shown to obey a simple, circular relationship.