INTERPHASE TRANSFER RATES IN EMULSIONS STUDIED BY NMR-SPECTROSCOPY

NMR line shape analysis has been used to monitor the rate of solute tr ansfer across interfacial layers around emulsion droplets. For this pu rpose, emulsions of o-xylene in water stabilized by nonionic emulsifie rs were prepared in which 1,4-dioxane was partitioned between the two phases. Because of the different magnetic susceptibilities of the xyle ne and water, two chemically shifted, exchange-broadened signals were observed from the dioxane. By simulating the spectra, the average resi dence time of a dioxane molecule in an oil droplet was obtained. The a verage time for a dioxane molecule to diffuse from within a droplet to the interface can be estimated from the droplet size distribution. Co mparison of the diffusion and residence times then gives the probabili ty that a dioxane molecule will transfer into the aqueous phase on arr ival at the droplet interface. Addition of alkali-metal halides to the aqueous phase reduced the probability of transfer. For sodium salts, the magnitude of the reduction is in the order F - > Cl- > I-. LiCl, N aCl, and KCl produced similar effects.