Rheology Test on Shear Viscosity of Surfactant Solution: Characteristic Time, Hysteresis Phenomenon, and Fitting Equation

A series of rheology tests on surfactant solutions (cetyltrimethylammonium chloride and sodium salicylate system, hereafter referred to as CTAC/NaSal) were performed in the present study. First we investigated the characteristic times (induction time and "plateau" time) of the viscosity variation process to study the effects of shear and temperature on micellar transition on the time scale. It was proved that the characteristic time has a power law dependence on shear rate. The power exponent varies around -1 and increases with temperature. By contrast, concentration influences the characteristic time little. Second the temperature-induced viscosity variation hysteresis phenomenon is studied for the first time. The viscosity variation obviously lags behind the varying temperature, and a "viscosity variation hysteresis circle" (VVH circle) is formed between curves tested under increasing and decreasing temperature. The shear-induced viscosity variation hysteresis also was studied from the induction time viewpoint. It was found that the hysteresis shows apparent power law dependence on both temperature varying rate (r) and shear rate, and the higher r or shear rate leads to the severer hysteresis. Third an equation is established to describe the correlation relation between viscosity and the influencing parameters of shear rate, temperature, and concentration. The calculated viscosity values from the equation agree well with the measured ones.