Perspectives of Phase Changes and Reversibility on a Case of Emulsion Inversion

The conventional treatment of catastrophic inversion is based on a two-phase model of oil-in-water (O/W) or water-in-oil (W/O). The present investigation takes a closer look at the process of inversion with focus on its relation to the detailed phase changes in the system. It is found that phase behavior inserts a decisive call for when the inversion starts and completes, even for an inversion seemingly brought by a simple change of water-to-oil ratio. The phases involved also play a critical role in the fine details of the emulsion structure, during both emulsification and evaporation. The presence of liquid crystal is instrumental in the inversion process as substantiated by the observation that its presence coincides with the presence of the intermediate multiple emulsions during emulsification. Multiple emulsions also appear during evaporation, though the mechanism of their formation is different from that during emulsification. The temporary stability of the multiple emulsions during both emulsification and evaporation is affected by the presence of the liquid crystal. It had been well established that the phase behavior plays a decisive role in transitional inversions and that the transformation to the inverse state is a gradual one. This is apparently also the case with the catastrophic inversion investigated here.