Wettability of quartz controlled by UV light irradiation using an azobenzene surfactant

Abstract

Solids having controllable wettabilty have received much attention due to their great importance in many industrial fields. In this paper, the quartz surfaces and particles with reversibly switchable wettability have been studied. The wettability of quartz can be controlled by UV light irradiation in the presence of an azobenzene surfactant (AZO). The adsorption behavior of AZO at the quartz-liquid interface was investigated by the measurements of the surface tension, contact angle and Zeta potential. The adsorption process was monitored by the quartz crystal microbalance with dissipation (QCM-D).The results show that AZO has a strong tendency to adsorb at the quartz–liquid interface. UV light irradiation causes the quartz-liquid interfacial tension (γsl) to decrease. The results from the QCM-D measurements show that the frequency change (Δf) decreases and the dissipation loss (ΔD) increases when AZO adsorbs onto the quartz surface. The dissipation changes are very small and the adsorption layer is rigid. After UV light irradiation, the adsorbed surfactants are desorbed from the quartz surface and the adsorption layer partly decomposes, causing the thickness of the adsorption layer to decrease.