Controllable adsorption and desorption of a cationic surfactant at quartz directed by host-guest complex

Abstract

The adsorption and desorption of surfactants play an important role in the industrial processes. We used cucurbituril (Q[7]) to tune the adsorption and desorption of a cationic surfactant at quartz. The cationic surfactant, N-Benzyl-N-hexadecyl dimethylammonium halide, can spontaneously absorb on the quartz surface. But when the absorbed surfactant at quartz reacts with Q[7] to form the host-guest complex, the absorbed surfactant is desorbed from the quartz surface. Adamantanamine hydrochloride was selected as another stronger guest molecule. Owing to the higher binding constant, Q[7] preferentially complex adamantanamine. Therefore, the surfactant molecules in the cavity of Q[7] are expelled to the water–quartz interface and absorb again on the quartz surface. In this manner, the adsorption and desorption of the cationic surfactant can be modulated. Through the measurements of the surface activity, contact angle and Zeta potential, we studied the adsorption and desorption of the cationic surfactant at quartz. The real-time adsorption and desorption of the cationic surfactant were monitored by the quartz crystal microbalance with dissipation (QCM-D). The surfactant aggregates on the quartz surfaces were scanned by the atomic force microscope (AFM). We expect to provide a way of tuning the adsorption and desorption of surfactants on solid surfaces.