Foaming behavior of fluorocarbon surfactant used in fire-fighting: The importance of viscosity and self-assembly structure

In this work, we systematically investigated the foaming behavior of a zwitterionic fluorocarbon surfactant (FC1157) used in fire-fighting. Two different foaming methods were used to generate foam, and the foaming behaviors of the fluorocarbon surfactant and typical hydrocarbon surfactants were compared. Multiscale approaches including cryogenic-transmission electron microscopy (cryo-TEM), surface tension measurements, viscosity and turbidity measurements were employed. Our results revealed that the foaming behavior of FC1157 is different from that of the hydrocarbon surfactants, which is not only related to the surfactant adsorption dynamics but also to the solution viscosity. We confirmed that the increased viscosity leads to a decrease in foaming ability and FC1157 is the only surfactant which exhibits viscous behavior in solution. The viscosity change is due to the variation in solution turbidity which comes from the formation of large aggregates in bulk. Cryo-TEM experiments indicated that FC1157 molecules tend to self-assemble in solution into vesicles. The presence of the vesicle phase strongly affects the solution viscosity and thus the foaming ability, which is different from that observed in the systems containing hydrocarbon surfactants. This study provided insight into the basic factors affecting the foaming behavior of the fluorocarbon surfactant used in fire-fighting, highlighting the crucial role of viscosity and self-assembly structure in determining the foaming behavior. (C) 2020 Elsevier B.V. All rights reserved.

Automated summary

This study systematically investigated the foaming behavior of a zwitterionic fluorocarbon surfactant used in fire-fighting, revealing differences compared to hydrocarbon surfactants in terms of surfactant adsorption dynamics and solution viscosity. The presence of vesicles formed by FC1157 molecules in solution strongly influences the solution viscosity and foaming ability, highlighting the importance of viscosity and self-assembly structure in determining the foaming behavior.