Interfacial Tension; a Stabilizing Factor for Janus Emulsions of Silicone Bixa Orellana Oils

The destabilization process was investigated for a Janus emulsion of silicone and Bixa Orellana oils stabilized by polyoxyethylene sorbitan monooleate (Tw 80) and carboxymethyl cellulose. The emulsion stabilized with Tw 80 showed significant and fast creaming, a process that was prevented by the addition of the polymer. During the extensive coalescence of the emulsions stabilized by Tw 80, the Janus topology was retained for months of storage until, finally, separation of the oils occurred. This result strongly indicates an unexpected stabilizing action of the i nterfacial free energy. This conclusion was supported by a calculation for a realistic model system of the interfacial energy difference between two cases of coalescence. In the first case, the two coalescing Janus drops united into a larger Janus drop, while in the second case two drops formed, each with only one oil. The first case gave a spontaneous reaction (reduced interfacial energy), while the second one meant an increase of energy, i.e. it cannot happen without adding energy. The authors are aware that this stabilization is a new phenomenon in emulsion science with potential ramifications in future emulsion technology. However, it is essential to realize that the stabilization is of temporary occurrence in the destabilization process, and the free energy to give a final emulsion state with separated oils is overwhelmingly dominant. In short, Janus emulsions will, in the end, separate into layers of the liquids, like all emulsions.