Study on rheology of novel UV/visible light sensitive trimeric cationic surfactant/trans-4-phenylazo benzoic acid micelle system

Abstract

The trimeric cetyl cationic surfactant (TGC) forms reversible photosensitive micelle systems with the photosensitive counterions trans-4-phenylazo benzoic acid (trans-ACA). The Carreau-Yasuda model was used for the flow curves before and after UV irradiation. The effects of trans-ACA concentration, TGC concentration, and different durations of UV (365 nm) and visible light (465 nm) irradiation on the rheological properties of TGC/trans-ACA were investigated. Prior to UV irradiation, the TGC/trans-ACA system was composed of wormlike micelles, which showed pronounced shear thinning behavior, good thixotropy and viscoelasticity. Macroscopically, it appears as a difficult to flow solution. After UV irradiation, trans-ACA is isomerized to cis-ACA, and the worm-like micelles are transformed to spherical or short rod-like micelles, resulting in a significant decrease in thixotropy and viscoelasticity, and thus a decrease in viscosity and an increase in fluidity. At lower TGC concentrations, UV irradiation can induce a reversal of the rheological properties of the TGC/trans-ACA system, which exhibits a complete solution state. Exposure to visible light restores the rheology of the system to that prior to UV irradiation. Under UV and visible light irradiation at different times, the system obeys to the rheo-kinetic equation. The UV–vis spectrum confirms that the changes in the rheological properties of the TGC/trans-ACA system are due to the reversible photoisomerization of trans-ACA.