Photoswitchable adsorption behavior on a silica surface: A comparison of the partially fluorinated surfactants with the hydrocarbon surfactants

Abstract

The surfactant adsorption at different interfaces is of great importance in surface science. We studied the photoswitchable adsorption/desorption of the partially fluorinated Gemini surfactants (CFS-2, CFS-6) at water-air and quartz-water interfaces. The fluorinated Gemini surfactants exhibit higher surface activity and lower wetting performance for quartz, compared to the comparable hydrocarbon ones (CHS-2, CHS-6). After UV light irradiation, the surface activity of the Gemini surfactants is decreased, and the wetting performances are increased. The adsorption mechanisms of the fluorinated Gemini surfactants at quartz were analyzed using the wetting data. The adsorption of the fluorinated Gemini surfactants at the quartz surface was further investigated by quartz crystal microbalance with dissipation (QCM-D) and AFM. The fluorinated Gemini surfactants exhibit greater adsorption at quartz compared to the comparable hydrocarbon ones. The fluorinated surfactants form rigid films at quartz. Upon UV light irradiation, the fluorinated surfactants exhibit the decreased adsorption at quartz and appear to be desorbed from quartz. The kinetics of the fluorinated surfactant adsorption at quartz was studied using the real-time measurement of QCM-D. Taken together, the findings in the present work provide insight into the significant differences in the surface properties and the adsorption onto the quartz surface between the partially fluorinated surfactants and the hydrocarbon surfactants.