Formation of stable aqueous foams on the ethanol layer: Synergistic stabilization of fluorosurfactant and polymers

The extreme instability of aqueous foams on the ethanol layer is an important issue to consider in the application of fire-fighting foams. We attempt making stable aqueous foams on the ethanol layer by using sodium dodecyl sulfate (SDS) as the foamer, with fluorosurfactant (FC1157) and xanthan gum polymers (XG) as the stabilizing agents. The surface properties, foam stability, and fire extinguishing performance of our studied systems were investigated respectively. The results show that ethanol destroys aqueous foams by dehydration and polar ethanol has a more significant defoaming effect than non-polar heptane. XG and FC1157 can inhibit the adverse effects of ethanol on foam stability. The addition of FC1157 improves the stability of the foam films and slows down the ethanol-induced dissolution of foams. XG polymers tend to form a gel-like membrane at the foam/ethanol interface, minimizing the mass transfer between foam and ethanol. The lifetime of foam stabilized by FC1157/XG is much longer than that of foam stabilized by FC1157 or XG alone in the presence of ethanol. Foams can go from unstable foams to foams being stabilized by both XG membrane and FC1157 synergistically. As a result, the synergism of FC1157 and XG in stabilizing foams significantly enhances the fire extinguishing performance of foam.