Rheological properties of fluorine-free foams stabilized by aluminum hydroxide nanoparticles and mixture of siloxane and hydrocarbon surfactants

Abstract

Fluorine-free foam stabilized by nanoparticle (NP) is expected to become a new generation of environmental-friendly firefighting foam. Many problems on properties of NP-stabilized fluorine-free foams remain to be studied. The present paper focuses on the rheology and foam stability of fluorine-free foam stabilized by aluminum hydroxide NPs. The surface tension, conductivity, foamability, viscosity, and viscoelasticity of mixed dispersions were measured. The stability, viscosity, viscoelasticity, and thixotropy of foam was analyzed deeply by model fitting and mechanism explanation. The results show that the rheological properties and foam stability of mixed dispersions are both enhanced by the presence of NPs, and the enhancement amplitude increased with NP concentration. Both dispersions and NP-stabilized foams exhibit shear thinning behavior, and the viscosity variations in dispersions conform to the Cross model well. As NP concentration increases, the linear viscoelastic range of foam becomes wider, the flow point of NP foam is delayed, demonstrated enhanced viscoelasticity. The thixotropic recovery of foam decreases with the increasing NP concentration, and foam thixotropic recovery decreases with the increase of irreversible deformation degree. This study can provide design idea for the development of fluorine-free firefighting foam.