Stability and rheological properties of foams co-stabilized by hydrophilic silica nanoparticles and amino acid/alkyl glycoside surfactants

Foams stabilized by nanoparticles (NPs) and surfactants have potential applications in the development of new environmentally friendly firefighting foams. In the present study, the mixed dispersions of anionic amino acid surfactant (SLG), nonionic alkyl glycoside surfactant (APG0810), and silica NPs were prepared. The influence of silica NPs on foamability, foam drainage, foam coarsening, and foam rheological properties of the mixture of SLG/APG0810 was systematically investigated. Results indicate that the presence of NPs results in decrease in conductivity and surface tension of the mixed dispersion. The viscosity of the mixed dispersions slightly decreases and then increases, while the foamability decreases following an increase with increasing NP concentration. The apparent viscosity of the mixed dispersions decreases over shear rate. The increase in NP concentration leads to rapid increase in viscoelastic modulus of the mixed dispersions and foams. The presence of NPs with concentration below 1 wt% results in acceleration of foam drainage and coarsening, while the presence of NPs with concentration above 1 wt% leads to deceleration of foam drainage and coarsening. This study offers theoretical support for the use of NPs in fluorine-free firefighting foams.