Experimental study on the mechanism of nanoparticles improving the stability of high expansion foam

Abstract High expansion foam (Hi-Ex) is recommended to suppress the leakage and diffusion of cryogenic liquid due to its light weight and large volume. However, the disadvantages of low stability and high break rate under environmental conditions are all limited the further application of the Hi-Ex foam in vapor mitigation and fire extinguishing. So that, this paper focus on the effect and mechanism of nanoparticles in stabilizing Hi-Ex foam. Three kinds of nanoparticles with different concentration were selected to evaluate the effect of foam half-life and the mechanism of solid particles on improving the foam stability. The results indicated that different particle concentrations can improve the foam stability to a specific extent, and the maximum improving of half-life can increase by 95.4% in presence of the hydrophilic SiO2 at 0.5 wt%. Meanwhile, the hydrophilicity, size and morphology of the particles have a specific impact on the foam stability. From the microscopic point of view, it was observed that the bubble size gradually increases with time by two processes of ripening and coalescence and satisfied in a logarithmic distribution. While, the liquid film thickness remarkably decreases in a large decline rate of 77.1% due to foam drainage without particles and the adsorption and accumulation of nanoparticles on foam lamella can provide a spatial barrier for the film thinning and the inter bubble diffusion. So that, the microscopic interaction mechanism of improving the foam stability between the nanoparticles and bubble have been further explored and revealed in these two aspects.