Recent Developments in Phase Inversion Emulsification

Abstract

Emulsions are multiphasic fluid systems in which liquid droplets are dispersed in another immiscible liquid. The main components of an emulsion are the two liquid phases, typically oil and water, and the emulsifier, which stabilizes the interface between the two liquid phases. Emulsifiers can be a variety of molecules, such as polymers, amphiphilic surfactants, and proteins, and they can also be colloidal particles. Emulsion phase inversion is the process of interconversion between two types of simple emulsions: water-in-oil and oil-in-water emulsions. Phase inversion can be induced by shifting the emulsifier affinity from one phase to the other, which is called transitional phase inversion. It can also be triggered by a change in the water-to-oil ratio of the emulsion, which leads to a process known as catastrophic phase inversion. With recent advances in the stabilization of emulsions using colloidal particles and stimuli-responsive surfactants, numerous novel emulsion systems that undergo emulsion phase inversion by means of various mechanisms have been developed. In this review, we highlight the most recent developments in the field of emulsion phase inversion, focusing on transitional phase inversion, inversion of particle-stabilized emulsions, and flowand shear-induced phase inversion. We also discuss and compare state-of-the-art analytical methods that have been used to detect and understand the emulsion phase inversion process. Our coverage spans from the early concepts of Bancroft's rule through the concept of semiquantitative hydrophilic−lipophilic balance to the more recent theoretical models used to predict and control phase inversion phenomena. We conclude this review by presenting an outlook on the future directions and outstanding problems that warrant future investigations to fully understand the mechanism of emulsion phase inversion at the single-droplet level.

Fabrication and characterization of nanoencapsulated epoxy resin/crosslinked PMMA shells with in situ polymerization via phase inversion emulsion (PIE) method

“…The transitional phase inversion involves the reversal of affinity of the surfactant for the two fluid phases. An attempt to relate surfactant behaviors to emulsion morphology was made by Bancroft's rule state that the phase (oil or aqueous) in which the surfactant is more soluble becomes the continuous phase in the resulting emulsion …”

“…Encapsulation of liquids and highly viscous polymeric resins can be conducted by phase inversion emulsification (PIE) method, which is a low‐energy technique to provide a stable emulsion for a variety of industrial products . Currently, it is well known that, in PIE, physicochemical properties of an emulsion are changed to invert the two phases: that is, from oil‐in‐water (O/W) to water‐in‐oil (W/O) emulsions, or vice versa …”

“…31,32 Currently, it is well known that, in PIE, physicochemical properties of an emulsion are changed to invert the two phases: that is, from oil-in-water (O/W) to water-in-oil (W/O) emulsions, or vice versa. 31,33 As can be seen from the literature, majority of the studies have been devoted to modification of polymer shells for micro/ nanocapsules by various methods such as polymerizing, crosslinking, and shell-thickness controlling to improve performance of capsules. However, there are rare number of studies regarding the influence of type and amount of crosslinking agent on leakage and durability of micro/nanocapsules.…”

The Horizon of the Emulsion Particulate Strategy: Engineering Hollow Particles for Biomedical Applications

“…[23] In a critical work, Ngai group produced W/O/W emulsions in a single step via polystyrene/poly(ethylene glycol) (PS/PEG) copolymers (toluene as the oil phase). [25] As a result, for certain coblock polymeric stabilizer, relative interfacial tension was regulated by tuning the volume ratio of the dispersed and continuous phases. For PEG 45 -b-PS 46 (asymmetric ratio = 1.02), the droplets were transformed from O/W to W/O/W emulsion by the increasing of the oil fractions, (Figure 3a-d).…”

Tuning Amphiphilicity of Particles for Controllable Pickering Emulsion

“…As a multiphasic mixture system, emulsions typically consist of three main components: oil phase, water phase, and emulsifier [8]. Various emulsifiers, including surfactants [9,10,11,12], polymers [13,14,15,16,17], proteins [18,19,20,21,22,23], and particles [24,25,26,27], have been utilized to prepare different kinds of emulsions.…”