W. G. Pritchard Lab Seminar: 3:30-4:30 PM, 102 McAllister Building

	          **Monday January 13, 2003**
	
Shear-banding and instabilities in complex fluids under shear: 
"phase separation"?

Peter D. Olmsted

Interdisciplinary Research Centre in Polymer Science
University of Leeds

Abstract:

"Shear banding", or flow-induced inducement of macroscopic "phase 
coexistence" has been observed in many complex fluids, including wormlike
micelles, lamellar systems, associating polymers, and liquid crystals. In
this talk I will review this behavior, and discuss a general phenomenology
for understanding shear banding and flow-induced phase separation in
complex fluids. To go beyond simple constitutive modelling of stress as a
function of strain rate, one must carefully consider the relevant
microstructural order parameter, and construct the fully coupled
hydrodynamic equations of motion. Although this has been successfully done
for very few fluids, we can nonetheless obtain general rules for the "phase
behavior". Perhaps surprisingly, the interface between coexisting phases
plays a crucial role in determining the steady state behavior, and is much
more important than its equilibrium counterpart. I will also touch on some
kinetic aspects of these "transitions".


    NOTE SPECIAL TIME AND PLACE: Mon 3:30-4:30, 102 McAllister