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

Abstract

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.

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BS-12 molecular structure.

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Surface tension­(mN/m) and conductivity­(μS/cm) of mixed dispersions at 25 °C.

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Initial foam height (mm) of mixed dispersions at 25 °C.

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(a) Photographs showing foam drainage over time for N-1# sample (b) Foam drainage volume (mL) as a function of time (s) for different dispersions at 25 °C.

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(a) Apparent viscosity (mPa·s) vs shear rate (s^–1) of mixed dispersions at 25 °C (b) r stress (Pa) vs shear rate (s^–1) curves for mixed dispersions.

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Viscoelastic properties of mixed dispersions at 25 °C: storage modulus (G′) and loss modulus (G″) vs shear strain (%).

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(a) Foam apparent viscosity (mPa·s) vs shear rate (s^–1) at 25 °C (b) Foam shear stress (Pa) vs shear rate (s^–1) curves for all foam types.

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Foam viscoelastic moduli (G′ and G″ in Pa) vs shear strain (%) at 25 °C.

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Thixotropic recovery behavior of foam samples at 25 °C: storage modulus (G′) and loss modulus (G″) vs time (s).