A study of the surfactant solution with reversible viscosity change by light stimulus

Abstract

Controlling frictional drag, noise, mixture, and chemical reaction in flow is an important issue in various engineering fields. In recent years, many investigations have been carried out to control the frictional drag by external stimuli, such as light and electricity, from the point of view of rheology and physical property. Flow control by the external light stimulus has a great advantage in that there is no contamination of the flow field. Some experiments of a photoresponsivity surfactant solution CTAB/C4AzoNa have been conducted for the basic study of flow control. The viscosity of the surfactant solution increased with the irradiation of ultraviolet (UV) light and decreased with visible light. First, we attempted to control the vortex height in the rotating flow by irradiating with UV and the visible light. The vortex height repeatedly increased and decreased by the reversible change in viscosity of the CTAB/C4AzoNa solution. Next, a thin layer of this solution in a vessel was exposed to blue laser sheet irradiation of 405 nm wavelength. As a result, the viscosity of the CTAB/C4AzoNa solution in the thin layer was locally increased at only the irradiated portion of the laser sheet. Finally, the CTAB/C4AzoNa solution filled a thin gap of the rotating two axial cylinder represented as a simple shear flow model. The torque acting on the inner cylinder surface was changed by local UV irradiation. These results proposed that this surfactant solution has the potential to achieve local and reversible flow control of drag.

Keywords

• flow control
• no-contamination
• photoresponsivity
• surfactant solution
• light stimulus