Study of mass transfer in oil-water-oil multiple emulsions by differential scanning calorimetry

摘要

A multiple emulsion of the type O1W/O-2 is studied experimentally by means of differential scanning calorimetry (DSC). The aim of this work is to characterize and measure the time-dependent changes within the emulsion. In particular, interest is focused to quantity the concentration changes in the internal and external phases of the O1W/O-2 multiple emulsion. In order to accomplish the objective, the measurement and analysis carried out by DSC are based on the crystallization behavior of the emulsion. A volume of a few mm(3) is periodically removed from the O1W/O-2 multiple emulsion. The sample is submitted to steady cooling and the crystallization thermogram is recorded. The experimental data provided by the crystallization thermogram makes it possible to quantity the crystallized mass for both phases, the internal and the external. In addition, the composition in each phase can also be deduced from the thermogram. To deduce the composition, a diagram of crystallization temperatures is elaborated, employing several mixtures of known composition. In addition to the main objective previously mentioned, the influence of formulation parameters such as surfactant concentration in the aqueous phase and the mass ratio of the internal and external phases are also analyzed. The experimental results made it possible to conclude that a mass transfer took place from the internal phase toward the external phase; this transfer is caused by the composition difference on both sides of the aqueous membrane. In this work we analyzed the mass transfer in the multiple emulsion carried out by a composition gradient through the aqueous membrane. The most likely mechanism of mass transfer through the aqueous membrane is a solution-diffusion of tetradecane enhanced by the micelles of the surfactant Tween 20. The model of mass transfer confirms that the osmotic pressure difference controls the kinetics of tetradecane transfer. It is also confirmed that an increment of surfactant concentration in the aqueous phase allows a faster kinetics of the tetradecane transfer. (c) 2005 Elsevier Inc. All rights reserved.