Experimental study on rheological properties of semidilute surfactant solutions

In order to investigate the effects of concentration and shear rate on rheological properties of semidilute surfactant solutions, CTAC/NaSal aqueous solutions with four mass fractions of 0.05%, 0.07%, 0.10%, and 0.15% were measured under the conditions of 25 °C and 1-300 s ^-1. The results show that the viscosity thickening rate caused by shear-induced transition decreases with an increase in the surfactant concentration at the same temperature until a critical saturation concentration arises. When the surfactant concentration is less than the critical saturation concentration, the shear rate-shear stress rheology curve σ (γ) satisfies the logarithm law in two regions of 1 s ^-1 to the critical shear rate and the critical shear rate to 300 s ^-1. Once the concentration reaches the critical saturation concentration, there is no shear-induced transition and the viscosity curve η (γ) at the critical saturation concentration is the maximum viscosity one. The possible formation mechanism of shear-induced structure (SIS) is presented by the shear energy analysis of the system. From the rheology, the SIS is no longer the necessary condition to generate turbulent drag reduction for semidilute surfactant solutions.