Gas-liquid interface properties of fluorocarbon and hydrocarbon surfactants and their mixed foams: Molecular dynamics simulations and experimental studies

Abstract

This paper focuses on the gas-liquid interface characteristics of short-chain fluorocarbon surfactant FS-50 and hydrocarbon surfactant sodium dodecyl sulfate (SDS) and their mixed systems. The foam properties of SDS, FS-50, and their mixed solutions were experimentally determined. Then, based on the molecular dynamics simulation method, the interaction mechanism of surfactant molecules at the gas-liquid interface was simulated and analyzed by constructing a foam-liquid membrane system containing surfactant molecules and water molecules. The experimental results show that FS-50 can effectively enhance the foam stability when the concentration is lower than 0.16 wt% and the mixing ratio with SDS is not more than 1:1; the simulation results show that FS-50 can change the arrangement of SDS molecules at the gas-liquid interface. Simultaneously, there is a competitive adsorption phenomenon between FS-50 and SDS at the gas-liquid interface. The low mixing ratio FS-50 can increase the thickness of the gas-liquid interface of the mixed system and the ability of SDS to form hydrogen bonds with water, enhance the water-locking ability of SDS, and further improve the stability of the foam liquid film. The interaction mechanism between short-chain fluorocarbons and SDS surfactants at the gas-liquid interface was revealed by simulation, which provided theoretical guidance for optimizing the performance of the foam liquid film.