Phase Inversion of Silica Particle-Stabilized Water-in-Water Emulsions

Abstract

An aqueous two-phase system (ATPS) is of great value in low calorie foods or oil-free cosmetics and pharmaceuticals. In contrast to the recent work on polymer/polymer ATPSs, a simple polymer/salt ATPS (polyethylene glycol/Na2SO4) was chosen to study water-in-water (w/w) emulsions stabilized by solid particles. The binodal curve and the tie lines were first determined for the mixture at room temperature. Above the binodal curve, two water-based phases coexist; the upper phase is rich in polymer, whereas the lower phase is rich in salt. Within the two-phase region, we attempted to prepare w/w emulsions with or without the addition of common emulsifiers. Ionic and nonionic surfactants, a polymer, and various solid particles (hydrophilic calcium carbonate particles of different sizes and shapes, wax microspheres) were selected, but no stable emulsion was possible. However, stable w/w emulsions of both types (polymer-in-salt and salt-in-polymer) were formed using dichlorodimethylsilane-modified nanosilica particles. Using partially hydrophobic fumed silica as the emulsifier, emulsions remained fully emulsified for over 1 year and we link the extent of hydrophobization of particles to the properties of the emulsions via contact angle measurements. Furthermore, systematic emulsion studies were conducted at different overall compositions such that changes in emulsion type and stability were mapped onto the phase diagram. Catastrophic phase inversion of emulsion type and evolution of emulsion stability were monitored along the tie lines. Importantly, stability to coalescence was found to decrease approaching conditions of phase inversion.

A new method to prepare microparticles based on an Aqueous Two-Phase system (ATPS), without organic solvents

“…Thus kinetic stabilization is required via adsorption of stabilizing species (copolymers [17] or particles) at the liquid-liquid interface or via interfacial complexation [10]. The strategy which consists of adsorbing solid particles at the interfaces of emulsion phases is called the Pickering method [18] and different kinds of particles such as silica [19], latex [20], or carboxylated particles [21], as well as with proteins such as blactoglobulin [22], whey protein [23] and zein-based nanoparticles [24] have already been studied to stabilize ATPS. In doing, among new perspectives in the area of ATPS, preparing biocompatible microparticles with a great potential in biomedical application is a current challenge [10].…”

Ultra‐Sensitive and Ultra‐Stretchable Strain Sensors Based on Emulsion Gels with Broad Operating Temperature

“…These observations were in good agreement with previous study: the rate of creaming or sedimentation depended on the droplet size and the viscosity of the continuous phase. Because the gravity induced the creaming of PEO droplet would be impeded at smaller droplet size and higher viscosity of the continuous phase [13,15,16] . By reason of the foregoing, emulsion in this study had good stability and there was no obvious changes on the droplet size after storing for 5 months at room temperature (Figure S4 in the Supporting Information).…”

Advanced biomedical applications based on emerging 3D cell culturing platforms

“…Since then, ATPS has gradually attracted attention and widely used in various industries. [36][37][38] At high concentrations, this systems can be formed easily by shearing a variety of substances in water. [39][40][41] Most of the research on ATPS has been focused on the separation of substances and purification products based on two incompatible polymer solutions and polymer-salt aqueous systems (e.g., phosphate, sulphate or citrate) with advantages over conventional extraction techniques.…”