Monday, September 15, 2014 1:00 p.m. RLM 11.204
Professor Joseph R. Gladden
Department of Physics
National Center for Physical Acoustics
The University of Mississippi
In viscous Newtonian fluids, support of shear waves is limited to the viscous boundary layer. However, non-Newtonian fluids, which have a shear modulus, support shear waves over much longer distances. Wormlike micellar fluids are an interesting class of non-Newtonian fluids in which surfactant molecules, aided by the addition of salts, self-aggregate into long and flexible cylindrical structures. The dimensions and topology of these structures depend on concentration, surfactant/salt ratio, and temperature. We will present studies in which acoustic shear wave propagation is used to better understand various structural phases of this system as a function of concentration and temperature. These studies indicate 2 distinct phase transitions between 0 (water) and 600 mM surfactant. Birefringent properties of this fluid make the acoustic field simple to visualize using crossed polarizers. We will also present neutron scattering results on microstructure, relaxation in static shear strain fields, and rheological studies to help flesh out the story on this complex fluid.