Effects of SiO₂ Nanoparticles and Polymers on the Rheology of Fluorine-Free Foam

To enhance the performance of fluorine-free firefighting foam, a mixed dispersion system comprising silica nanoparticles (SiO₂ NPs), guar gum (GG), and surfactants was developed and systematically evaluated. Compared with systems containing only NPs or GG, the combined formulation significantly improved foam stability and rheological properties. The optimized GG-NPs formulation exhibited the lowest drainage volume and the highest storage modulus, indicating enhanced structural integrity. Rheological analysis revealed strong shear-thinning behavior and a high zero-shear viscosity, with Cross model fitting confirming structural consistency across shear rates. Thixotropic tests showed that the foam could recover over 76% of its original elasticity after shear disruption. These improvements are attributed to the synergistic interaction between GG and NPs, forming a network that reinforces both the foam film and bulk liquid phase. This study provides quantitative insight into NPs-polymer synergy in foam systems and presents a scalable, environmentally friendly formulation with potential to meet modern fire safety performance standards.