Particles’ Organization in Direct Oil-in-Water and Reverse Water-in-Oil Pickering Emulsions

Abstract

This paper addresses the impact of the particle initial wetting and the viscosity of the oil phase on the structure and rheological properties of direct (Oil/Water) and reverse (Water/Oil) Pickering emulsions. The emulsion structure was investigated via confocal microscopy and static light scattering. The flow and viscoelastic properties were probed by a stress-controlled rheometer. Partially hydrophobic silica particles have been employed at 1 and 4 wt.% to stabilize dodecane or paraffin-based emulsions at 20 vol.% of the dispersed phase. W/O emulsions were obtained when the particles were dispersed in the oily phase while O/W emulsions were prepared when the silica was introduced in the aqueous phase. We demonstrated that, although the particles adsorbed at the droplets interfaces for all the emulsions, their organization, the emulsion structure and their rheological properties depend in which phase they were previously dispersed in. We discuss these features as a function of the particle concentration and the oil viscosity.

Cellulose Acetate-Stabilized Pickering Emulsions: Preparation, Rheology, and Incorporation of Agricultural Active Ingredients

“…A possible explanation for this is the inability of the particles to migrate from the water phase to the oil phase during emulsification. Experimental evidence of this is found in a recent study wherein the authors report the stabilization of both O/W and W/O emulsions from hydrophobic particles, depending on which phase the particles are initially dispersed in. There, the dispersion of particles in the water phase prior to emulsification resulted in an O/W emulsion and conversely.…”

Amphiphilic titania Janus nanoparticles containing ionic groups prepared in oil–water Pickering emulsion

“…49–51 The formation of such Pickering emulsions depends on the oil to water volume ratio, as well as on the particles wettability and the phase the particles were initially dispersed in ref. 49, 52 and 53. Because the particles were first dispersed in water, the emulsification process leads to O/W emulsions instead of W/O emulsions.…”

“…This anti-Bancroft behaviour was previously observed for other systems, like partially hydrophobic silica particles for O/W emulsions and charged latex particles for W/O emulsions. [49][50][51] The formation of such Pickering emulsions depends on the oil to water volume ratio, as well as on the particles wettability and the phase the particles were initially dispersed in ref. 49, 52 and 53. Because the particles were first dispersed in water, the emulsification process leads to O/W emulsions instead of W/O emulsions.…”

Bicontinuous Interfacially Jammed Emulsion Gels (Bijels): Preparation, Control Strategies, and Derived Porous Materials

“…The liquid-liquid interface stabilizer of colloid particles originates from the Pickering emulsion, which was discovered in the early 20th century by Ramsden [1] and Pickering [2]. Compared with traditional emulsions stabilized by surfactants, the solid film formed by the selfassembly of colloidal particles at the oil-water interface can protect the microdroplets against coalescence and Ostwald ripening [3,4]. According to the thermodynamic model established by Pieranski [5], for a single spherical solid particle with an effective radius of r, the reduction in the system free energy is the main driving force for particle assembly at the liquid-liquid interface.…”