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Diffusion in an inhomogeneous system: NMR studies of diffusion in highly concentrated emulsions
Carin Malmborg1, Daniel Topgaard, Olle Söderman
1Division of Physical Chemistry 1, Center for Chemistry and Chemical Engineering, Lund University, P.O. Box 124, SE-221 00 Lund, Sweden. carin.malmborg@fkem1.lu.se
Abstract:
In this study the self-diffusion of different species in highly concentrated water-in-oil emulsions was investigated by means of the NMR diffusometry approach. The emulsions contained 96% aqueous solutions of salt or other additives; heptane was used as the oil phase. The surfactants, used to stabilize the emulsion, were soybean phosphatidylcholine and C(12)EO(4). The water drops were about 1.5 microm in diameter according to diffusion measurements performed on water. Diffusion of tetramethyl ammonium ions and glucose between the emulsion droplets was found to be negligible on the relevant time-scale (<1 s). On the contrary, acetic acid/acetate ions diffused between the droplets and had exchange times which were a function of pH.