W. G. Pritchard Lab Seminar: 4-5 PM, 116 McAllister Building

	          **Tuesday April 2, 2002**
	
Living and Dead Polymers: Rheology and Structure of Complex 
  Multicomponent Fluids

Lynn M. Walker

Department of Chemical Engineering
(Center for Complex Fluids Engineering)
Carnegie Mellon University

Abstract:

The dynamics of wormlike micelles are analogous to semi-dilute polymer
solutions, with additional relaxation mechanisms due to the aggregate
nature of the micelles. The rheology of these systems is controlled by
the microstructure of the micellar aggregates. While the aggregation
of surfactants and polymers in solution has been studied extensively,
the ramifications of such assembly on the rheology of systems
involving wormlike micelles have not been investigated at a
fundamental level. 


We are quantifying the rheology and flow-induced structure of mixed
systems of wormlike micelles and nonionic, aqueous polymer. We have
found significant differences in the rheology of mixtures of
cetyltrimethylammonium tosylate (CTAT) and specific nonionic polymers;
differences controlled by polymer architecture and physicochemical 
properties. Local micellar structure is probed with a combination of
small-angle neutron scattering and static light scattering. The
details of assembly and its influence on structure and macroscopic
rheology have been quantified for a series of nonionic polymers,
focusing on the availability of hydrophobic moieties in those
polymers. Results provide the fundamental understanding necessary to
tune the rheology of micellar solution and provide guidelines in
formulation design. The rich behavior of these materials will also be
demonstrated with the influence of added electrolyte and in situ
polymerization.