Transitional phase inversion of solid-stabilized emulsions using particle mixtures

For emulsions containing equal volumes of toluene and water stabilized by nanometer-size silica particles alone, we demonstrate that transitional inversion, from oil-in-water (o/w) to water-in-oil (w/o) and vice versa, can be achieved using mixtures of two particle types of different wettability. Using conductivity, stability, light diffraction, and optical microscopy measurements, we detail three main ways of effecting this which include addition of hydrophilic silica to w/o emulsions stabilized by hydrophobic silica, addition of hydrophobic silica to o/w emulsions stabilized by hydrophilic silica, and varying the weight fraction of one of the particle types at constant total particle concentration. Although both types of emulsion are very stable to coalescence, the stability to creaming of o/w emulsions and to sedimentation of w/o emulsions is least around conditions of inversion, consistent with the average drop sizes displaying a maximum. An increase in the proportion of charged hydrophilic silica results in denocculation of the drops in w/o emulsions.