The aqueous film forming foam (AFFF) is a highly effective for pool fire suppression. However, the fluorocarbon surfactants contained in AFFF are not very biodegradable and cause severe environmental problems because of the highly stable C-F bonds. Therefore, it is critical to develop fluorine-free surfactants that can minimize the fuel vapor transport through the lamellae (bubble walls) and increase lamellae stability for effective fire suppression. The objective of this work is to study the properties of the surfactant monolayers at fuel/water and air/water interfaces, and their interactions with the fuel by molecular dynamics (MD) simulations. A valid computational model of the lamella interfaces in the aqueous foam can be used to develop understanding of the dependence of lamella properties on the surfactant’s molecular structure. This will provide structural features of potential surfactants for synthesis and experimental investigations, and facilitate the development of new and effective firefighting aqueous foams. To reach this goal, in the current stage, we simulated two hydrocarbon surfactants, a perfluorocarbon surfactant, and a siloxane surfactant. The MD simulated surface area per surfactant molecule and surface tension agree well with experimental data, which validate the force field and simulation method used. The other properties of interfaces, such as interfacial tensions, Gibbs elasticity, and zeta potential, are also computed and compared to the available experimental or computational data in the literatures to further validate the method. The interfacial thicknesses, and the radial distribution function are obtained for better understanding of the interface systems.

Molecule dynamics simulations of the fluorinated and fluorine-free surfactant monolayers at air-water and heptane-water interfaces

255th National Meeting (2018)

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