Emulsion multiple de type L/H/L: étude de l'obtention et du mécanisme de libération

Synopsis An O/W/O multiple emulsion was formulated using almond oil as the inner phase and liquid paraffin as the outer phase. The properties of the formulation ingredients were explored: effect of the type of primary emulsifier, and the nature and concentration of the secondary emulsifier. The volume fraction of the internal phase in the multiple emulsion was also optimized with regard to the stability. The multiple systems were assessed by evaluating several parameters such as the macroscopic aspect, the droplet size, the direction of the dispersion and the accelerated stability under centrifugation or elevated temperature. The effect of some additives (ozokerite, benzyl alcohol and glycerol) was examined. Whatever additive was used, a decrease in the formulation stability, which could be attributed to different phenomena, was observed. Furthermore, an analytical procedure was developed for studying the release of an active principle, alpha-tocopherol (vitamin E). This release could be a result of the instability of the multiple droplets or a diffusion through the water layer membrane. This procedure was based on the difference of chemical type between the two oil phases: mineral outer phase and fatty inner phase. Two chromatographic methods were used: a gas chromatographic assay of oleic acid which is the main component of the fatty phase, and a liquid chromatographic assay for the alpha-tocopherol, encapsulated in the inner phase. The presence of oleic acid in the paraffin phase originated from a rupture of the multiple droplets, whereas the presence of alpha-tocopherol in the outer phase could be due both to a diffusion phenomenon and to the instability of the formulation. The results obtained showed that only the rupture of the droplets occurred. Moreover, a part of the alpha-tocopherol was retained by Hypermer A 60 used as an emulsifier in the formulation.