Synergistic Stabilization of Emulsions by a Mixture of Surface-Active Nanoparticles and Surfactant

Abstract

The stability and rheology of tricaprylin oil-in-water emulsions containing a mixture of surface-active hydrophilic silica nanoparticles and pure nonionic surfactant molecules are reported and compared with those of emulsions stabilized by each emulsifier alone. The importance of the preparation protocol is highlighted. Addition of particles to a surfactant-stabilized emulsion results in the appearance of a small population of large drops due to coalescence, possibly by bridging of adsorbed particles. Addition of surfactant to a particle-stabilized emulsion surprisingly led to increased coalescence too, although the resistance to creaming increased mainly due to an increase in viscosity. Simultaneous emulsification of particles and surfactant led to synergistic stabilization at intermediate concentrations of surfactant; emulsions completely stable to both creaming and coalescence exist at low overall emulsifier concentration. Using the adsorption isotherm of surfactant on particles and the viscosity and optical density of aqueous particle dispersions, we show that the most stable emulsions are formed from dispersions of flocculated, partially hydrophobic particles. From equilibrium contact angle and oil-water interfacial tension measurements, the calculated free energy of adsorption E of a silica particle to the oil-water interface passes through a maximum with respect to surfactant concentration, in line with the emulsion stability optimum. This results from a competition between the influence of particle hydrophobicity and interfacial tension on the magnitude of E.

Polystyrene/nano-SiO2 composite microspheres fabricated by Pickering emulsion polymerization: Preparation, mechanisms and thermal properties

“…Such materials provide a new class of supramolecular building blocks and are likely to exhibit unusual, possibly unique properties [14]. So far, the preparation and forming principle of Pickering emulsion have been well documented by Binks and coworkers [15][16][17], Midmore [18], and Bon and coworkers [19,20] Moreover, a series of nanocomposite microspheres have been prepared. Bon and Colver [21] reported the fabrication of a variety of armored latex by Pickering miniemulsion polymerizations using Laponite clay discs as stabilizer.…”

Magnetic nanoparticles-induced anisotropic shrinkage of polymer emulsion droplets

“…Some research groups reported that liquid droplets coalescence or particle detachment was induced when surfactant was added into Pickering emulsions or bubbles due to the adsorption of the surfactant on the particles surface. 26,27 At a high concentration of surfactant, particles were even replaced by surfactant molecules. 28 In our experiments, the surfactant concentration is high (1 wt%).…”

Rheological properties of emulsions formed by polymer solutions and modified by nanoparticles

“…Figure 2 demonstrates the results of the Bapparent viscosity^measurements (defined as the ratio of current stresses to a specified shear rate). As is seen, a pronounced transient (1) or additionally with 0.5 wt.% NaD (2) or MMT (3) process happens reflecting the unlimited increase of apparent viscosity with the tendency to the yield stress, just as was described in [25][26][27].…”

“…So-named Pickering emulsions stabilized by solid micro-or nanoparticles were studied in numerous publications [1][2][3][4][5][6][7][8]. Usually the subject of these studies was classical oil-in-water or reverse emulsions.…”