Chapter 3 - Catastrophic Phase Inversion Techniques for Nanoemulsification

Abstract

Nanoemulsions can be fabricated using the catastrophic phase inversion (CPI) method by exploiting either surfactants or solid particles. This emulsification method is also sometimes known as the phase inversion composition or emulsion inversion point method and is based on gradually diluting, under mild flow conditions, one liquid (such as water) with another immiscible liquid (such as oil) until phase inversion occurs and a nanoemulsion is formed (such as oil in water). Usually, the inversion of the phases is signaled by the appearance of an intermediate phase with specific physicochemical properties that is broken down during the emulsification process, thus giving rise to small droplets. The name CPI was termed because researchers thought that this process could be described using catastrophe theory. However, the physicochemical mechanisms associated with phase inversion cannot always be described using this theory because there are too many hydrodynamic and physicochemical variables to account for. Despite the lack of an analytic model capable of including both the hydrodynamics and physical chemistry of the system and of describing the complex morphological changes associated with this phenomenon, CPI can still be used successfully to encapsulate many active compounds (such as pharmaceuticals, vitamins, nutraceuticals, antimicrobials, colors, and flavors) in nanoemulsions. In addition, our current mechanistic understanding allows nanosized droplet dimensions to be roughly predicted for systems prepared using pure single surfactants. This chapter provides an overview of the current understanding of the theory and practice of nanoemulsion production using the CPI method.