Transport properties of W/O highly concentrated emulsions (gel-emulsions).

W/O highly concentrated emulsions formed in ternary water-nonionic surfactant-hydrocarbon systems consist of water droplets dispersed in a microemulsion phase. These emulsions show structural, rheological and optical properties that make them good candidates for the cosmetic and pharmaceutical industry as delivery systems. In addition, their high content of water and low concentration of surfactant and oil makes them attractive for economical, environmental and toxicological reasons. Our previous studies on their preparation, formation, structure and mechanical properties allow us to understand the basics underlying the transfer of added molecules. In order to study the transport properties of these systems, we have undertaken two types of experiment. In the first type, an emulsion with an added molecule is brought in contact with the same emulsion without additive. The concentration profile of the additive in both emulsions is determined after the system has evolved for a certain time. This allows for the determination of a global diffusion coefficient. In the other type of experiment the emulsion containing an added molecule is immersed in water. The release of the added compound from the emulsion to the receptor solution is monitored as a function of time. We model the diffusion behaviour with a microscopic model that takes into account the microstructure of the system. We present some results showing the modulation of the diffusion by changes of the composition variables. [ABSTRACT FROM AUTHOR]