MASS transfer of a solubilizate in a micellar solution and across an interface

A water insoluble material, when it is to be moved through a water phase to be delivered into an oil phase, can be conveniently solubilized in a deter gent micelle. In that form, it can exist in water at higher concentrations and pass easily into the oil phase for which it has a higher affinity. We h ave measured the mass transfer rates in water as well as those across the i nterface. The mass transfer rates in such systems are very low which make t hem difficult to measure. An experimental setup which is capable of making these measurements is presented. A spatio-temporal variation of concentrati on is induced inside a spectrophotometer cuvette. As the System moves towar d equilibrium under diffusion, the change in concentration with time is mon itored by measuring the absorbance of the solution. The solution to the app ropriate boundary value problem is used to back calculate the diffusivity a nd interfacial resistance from the absorbance data using the fact that abso rbance is linearly dependent on concentration. Satisfactory values of diffu sivities are reported for simple solutes and a surfactant, sodium dodecyl s ulfate, SDS (the last has been reported earlier, Neogi, 1994) in water. Thi s technique has been used to measure the transport of nitrobenzene from SDS micelles to squalane. The results indicate significant interfacial resista nce. A quantitative model has been provided for the first time.