Rheological and flow birefringence studies of a shear‐thickening complex fluid—A surfactant model system

Abstract

A common surfactant solution system is investigated to demonstrate the characteristic and generic features observed in shear‐thickening self‐assembling fluids. Rheological and flow birefringence measurements on the aqueous CTAB/sodium‐salicylate solutions disclose a number of unusual flow behaviors under different flow conditions. All solutions with concentrations ranging from 0.5 to 5 mM exhibit shear thickening above certain critical shear rates, accompanied by an increase in flow birefringence over a range of temperature from T=14 to 36 °C. An extraordinarily long induction period, which is found to be inversely proportional to the applied shear rate, precedes the establishment of the shear‐thickening state. This dynamic state is highly flow birefringent, strongly nonlinear viscoelastic and possesses long relaxation times. We deduce that shear‐induced coagulation results in self‐assembling of surfactant molecules to form new micelles which are of exceedingly large sizes and which can survive against th...