Experimental study on nano-SiO2 particles regulating the performance of fluorine-free foam and its fire extinguishment effectiveness

To address the environmental risks posed by PFOS-containing fire extinguishing agents, the development of highly efficient and environmentally friendly fluorine-free foam extinguishing agents has become a forefront research area in the firefighting community. In this study, a novel foam extinguishing agent was prepared using the nonionic silicone surfactant SiCare2238 and the amphoteric hydrocarbon surfactant LAMC as core components, with hydrophilic nano-SiO₂ particles (NPs) introduced to construct a gas–liquid-solid three-phase fluorine-free foam system. By regulating the NP concentration, the interactions of NPs and surfactants and the resulting effects on the foam performance were investigated. The results indicate that when the NP concentration is < 1 wt%, the charge interactions between particles and surfactants weaken the interfacial adsorption, leading to accelerated drainage and coarsening, thereby reducing the foam stability. In contrast, when the NP concentration is ≥ 1 wt%, the particles form a dense network in the Plateau borders, blocking the Plateau channels, resulting in a 47.4 % reduction in drainage within 30 min and a 30 % decrease in coarsening rate, significantly enhancing the foam stability. Moreover, the fire extinguishing and burn-back experiments demonstrated that the SN-7# system with 5 wt% NPs achieved a 90 % flame control time of 17 s and an extinguishing time of 26 s, outperforming the commercial AFFF and the NP-free SN-0#. The addition of NPs significantly enhances fire suppression efficiency, as they interact with surfactants in foam films and Plateau borders to form aggregated network structures, effectively delaying the drainage and coarsening, thereby improving the foam’s thermal stability and burn-back resistance. The findings of this study provide theoretical guidance for the development and application of NPs in fluorine-free foam extinguishing agents.