High Internal Phase Emulsions Stabilized Solely by Functionalized Silica Particles

Abstract

High Internal Phase Emulsions (HIPEs) are important for a wide range of applications in the food, cosmetic, pharmaceutical and petroleum industries. If the continuous phase is polymerizable, HIPEs can be used as templates for the synthesis of highly porous polymers with potential applications as low weight structures or scaffolds in tissue engineering. HIPEs are characterized by a minimum internal phase volume ratio of 0.74 but Lissant first defined this minimum as 0.7. HIPEs consisting of a continuous organic phase and an internal aqueous phase (w/o emulsion), are commonly stabilized by large amounts of surfactants. Particle-stabilized emulsions also known as Pickering-emulsions have recently attracted much interest. Unlike surfactants, particles irreversibly adsorb at the interface of emulsions due to their high energy of attachment which makes them good emulsifiers. The ability of particles to adsorb at the interface between the two phases is primarily dependent on the wettability of the particles. Hydrophilic particles such as metal oxides tend to stabilize o/w emulsion while hydrophobic particles such as carbon tend to stabilize w/o emulsions. Nevertheless, it is possible to modify the wettability of particles by adsorbing surfactant molecules onto the particle surfaces or by silanation. All reports on particle-stabilized emulsions deal with emulsions having internal phase levels elow 70 vol.-%. Kralchevsky et al. developed a thermodynamic model, which predicts that