Effect of hydrophilic silica nanoparticles on foam properties of mixtures of silicone and hydrocarbon surfactants

Foams stabilized by nanoparticles (NPs) and surfactants have great application prospects in the development of fluorine-free firefighting foams. In the present study, hydrophilic SiO2 NPs, a nonionic silicone surfactant (CoatOsil-77), and a zwitterionic hydrocarbon surfactant (BS-12) were used to prepare mixed dispersions to investigate effect of NPs on properties of fluorine-free foams. The interactions between NPs and surfactants, foaming ability, and foam stability of the mixed dispersions were investigated. Results indicate that the surface activity, conductivity, and foaming ability of the mixed dispersions decreased with increasing NP concentration. The addition of NPs has a remarkable impact on foam stability of the mixed dispersions. The presence of NPs at a NP concentration above 2% leads to enhancement of foam stability by delaying foam drainage and coarsening. This study provides theoretical guidance for the application of NPs in fluorine-free foams.