Study Of The Preparation And Stability Of Water-in-oil (W/O) Emulsions Based On Phase Inversion

Emulsions are kind of thermodynamically-unstable dispersions of one immiscible liquid phase in another, which have been applied widely in the fields of petroleum, chemical, pharmaceutical and food. However, the majority of published works specifically focus on O/W emulsions. For the inverse W/O one, articles are relatively few. W/O mulsions, despite a late start, plays an irreplaceable role in the actual production, such as paint, food, cream, metal cutting fluids and oil-based drilling fluids. Therefore, it is of great importance to study the preparation and stability of W/O emulsions. In addition, the emulsion phase inversion is a reversed process of continuous phase and dispersed phase. In many cases, this is the unstable performance of the emulsion, which is unfavorable to us. However, in certain circumstances, the phase inversion could be used to prepare the emulsions with high performance. This shows that the phase inversion has dual characteristics, which requires our fully understanding of the phase inversion process to artificially control it. When it was undesirable, some effective methods could be adopted to avoid its occurrence. When it was available, a better performance emulsion could be prepared owing to its unique advantage.In this thesis, aiming at the shortcomings of current research on W/O emulsions and double peculiarities of phase inversion, we focus on the following two opposing but interrelated aspects:how to avoid the occurrence of phase inversion when the emulsions need to keep stable; on the other hand, how to take advantage of the special peculiarities of phase inversion to prepare the W/O emulsions with high quality.Firstly, the relationship between the phase inversion and the formation or stability of the W/O emulsions was discussed in detail. In water/Polyoxyethylene4lauryl ether/paraffinic oil system, we adjust the phase inversion temperature through changing temperature and inorganic salt concentration. In addition, the formation conditions and stability conditions of W/O emulsions were studied. Secondly, we apply the phase inversion to prepare high performance W/O emulsion. In the system of water/Span80-Tween80/white oil, with the adjusted temperature and composition, we successfully prepared W/O nanoemulsions by stirring only. Comparing with the existing ones, this method was able to fabricate monodisperse W/O nanoemulsions with an inner water phase up to30vol.%. The water droplet size of this nanoemulsions was determined by dynamic laser light scattering (DLS), which was found to be within the range of50-300nm. They showed excellent stability against Ostwald ripening due to the extremely low solubility of water in the continuous paraffin oil phase. This new low energy emulsification method may have significant applications in industries.