Study of Inclusion in Phase InversionEmulsification and Multiple Emulsions

Abstract

The phenomenon of ‘inclusion’ in emulsions refers to the inclusion of continuous phase into the dispersed phase drops and formation of multiple drops due to the tendency of the inner phase to stabilise the outer phase. Inclusion plays an important role in both catastrophic phase inversion (CPI) emulsification process and preparation of multiple emulsions. In CPI, inclusion leads to formation of abnormal multiple drops, which eventually invert to the opposite desired normal emulsion. On the other hand, in multiple emulsions, inclusion may have an adverse effect leading to instability of the multiple emulsions because of coalescence of inner drops, and/or coalescence of multiple drops, or even bursting of multiple drops. All these result in instability of multiple emulsions and accelerate release of the active agent. In the first part of this work, we carried out a comprehensive study on the rate and extent of inclusion in CPI emulsification at different formulation and process conditions for the first time. We also investigated the conditions under which the CPI emulsification method produces finer emulsions than the direct emulsification method, which means applying less energy could result in a finer emulsion. In the second part of this work, we investigated the conditions under which inclusion can be ignored during the preparation of multiple emulsions. We also carried out an extensive study on the optimisation of the process conditions to achieve maximum encapsulation efficiency in freshly prepared multiple emulsions. In the last part of this work, we briefly looked at the possibility of synthesis of macroporous alginate hydrogel particles via CPI and through inclusion of an oil into sodium alginate drops but without success. However, we introduced a new modified emulsification process based on addition of calcium chloride water-in-oil emulsion to sodium alginate emulsion, which produced promising results.