Study on the relationship between surface tension and dilational visco-elasticity with foam stability

Abstract

The replacement of fluorine-free foam is imminent, but to date, no fluorine-free foam has reached comparable fire extinguishing performance to AFFF (aqueous film forming foam). The stability of firefighting foam significantly affects its extinguishing performance. In order to better understand the influence of foam formulation physical properties on foam stability, we correlate the foam stability with surface tension and dilational visco-elasticity based on the AFFF formulation. The results show that, the foam stability rising steadily with the decrease of surface tension, which indicates that low surface tension favors the improvement of foam stability. However, when at the studied highest surface tension, the foam stability elevates slightly instead, demonstrating the surface tension is not the determinant of foam stability. By contrast, the dilational visco-elasticity shows a closer correlation with foam stability for the consistent tendency. In the case of constantly changing disturbance frequency, the interface dilational elasticity shows a trend of first increasing and then decreasing with the rise of disturbance frequency, whereas the interface dilational viscosity is completely opposite. Different relaxation processes show up for different samples. More attention can be paid to the regulation of dilational visco-elasticity in the development of fluorine-free foams, so as to improve their extinguishing ability.