Effect of Adsorbed Monomolecular Films on the Evaporation of Volatile Organic Liquids

摘要

An investigation was made of the effect of adsorbed surface-active films on the rate of evaporation of volatile organic liquids. A series of partially fluorinated compounds were studied either as monolayers adsorbed from solution or as insoluble films spread at the liquid/vapor interface. In no instance was the rate of evaporation significantly reduced by the presence of a monomolecular film. Insoluble multimolecular films of polydimethylsiloxanes, however, were found to reduce effectively the rate of evaporation, provided the film thickness was sufficient to decrease the rate of diffusion of the solvent molecules through the film to a value below their rate of diffusion through the saturated, nonturbulent vapor layer overlying the surface. In addition to polydimethylsiloxane polymolecular layers, thin layers of water, containing suitable fluorocarbon spreading agents, were also found to reduce the rate of evaporation of certain volatile organic liquids. These aqueous films are similar to the thin layers of interlamellar water present in aqueous foams used to extinguish gasoline fires, such as the fluorocarbon-containing Light Water foams. (Author)