Influence of multi-type nanoparticles on the foam thermo-rheological properties of mixtures of short-chain fluorocarbons and hydrocarbon surfactants

While nanoparticles (NPs) are known to enhance the rheological properties of firefighting foams, the impact of different NPs types on the foam thermo-rheological properties has remained unclear. Short-chain fluorocarbon and hydrocarbon surfactants, and three types of NPs (SiO₂, Al(OH)₃, and β-Al₂O₃) were used to prepare the foams. The interactions between NPs and surfactants, as well as their effects on foaming ability, foam stability, and foam thermo-rheological properties, were analyzed. Results indicated that NPs can form aggregates with surfactant molecules, thereby affecting surface tension, pH value, conductivity, zeta potential, viscoelasticity, and viscosity of foam dispersion. NPs can reduce the initial foam height of the foam dispersion from 340 mL to 250–260 mL, and significantly decrease the foaming ability. All three NPs could significantly delay foam drainage and enhance foam stability. At 45 °C, the NPs can decrease foam viscosity and viscoelasticity. The thixotropy of all foams at 45 °C showed different trends, and the foam with Al(OH)₃ NPs showed the best thixotropic structure recovery. Hysteresis behavior at 45 °C of the foam with Al(OH)₃ NPs decreased, but increased in the foam containing SiO₂ and β-Al₂O₃. In general, all three NPs could enhance the foam stability and foam thermo-rheological properties, with Al(OH)₃ demonstrating the strongest capability. This study can provide theoretical support for the development of firefighting foam stabilized by NPs.