Temperature dependence of shear wave speed in a viscoelastic wormlike micellar fluid

Abstract

Wormlike micellar (WM) fluids are viscoelastic and can support shear waves. The topologies of microstructures in these WM fluids depend on temperature, concentration and other physical conditions. In this work, the dependence of shear speed with temperature of 200mM CTAB (Cetyltrimethylammonium bromide) /NaSAL (sodium salicylate) micellar fluid in a 5:3 ratio was studied. Shear wave propagation through the fluid was observed as a time varying birefringence pattern by using a high speed camera and crossed polarizers, and shear speed was calculated by an edge tracking technique. Three distinct temperature-dependent regimes of shear wave speed were observed in the temperature range of 20-45⁰C. The boundaries between these regimes were at about 28⁰C and 38⁰C. These temperature-dependent, distinct regimes of shear wave speed suggest different phases in the microstructure of the self-assembled surfactant system which may arise from changes in the micellar structure at the microscopic level.