Oil resistivity of fluorine-free foams stabilized by silica nanoparticles and mixture of silicone and hydrocarbon surfactants

This study aims at exploring properties of fluorine-free foams co-stabilized by nanoparticles (NPs) and surfactant. The mixed dispersion liquids composed of silica NPs, nonionic hydrocarbon surfactant (APG-0810), and organosilicon surfactant (CoatOsil-77) was prepared. The NP-intensified foams under the action of n-heptane (flammable liquid) were focused by analyzing aggregation behavior of surfactants, initial foaming height, foams drainage and decay, and single vertical film stability of the mixed dispersion liquids. The findings show that the presence of surfactants improves surface activity of water obviously. After adding NPs, the interactions between surfactant molecules are destroyed but new aggregates formed. Foaming ability decreases but stability increases significantly with increasing NP concentration. After n-heptane is added, intensified interactions exist among surfactant molecules, NPs, and oil droplet, promoting formation of some larger aggregates and increasing the surface tension and viscosity but decreasing the conductivity and foaming ability. In addition, the presence of n-heptane accelerates foam drainage and volume decay and thinning process of the vertical liquid film. NPs with an appropriate concentration can improve foaming ability, foam stability, and the corresponding oil resistivity of foam. This study can provide theoretical guidance for the development of new fluorine-free foams used for liquid fuel fire.