Catastrophic phase inversion of emulsions stabilized by amphiphilic nanoparticles

Phase inversion of water-in-oil (W/O) emulsion to oil-in-water (O/W) emulsion is investigated experimentally by varying the volume fraction of water, in the presence of silica nanoparticles in the oil phase at different concentrations. The influence of hydrophobicity of nanoparticles on phase inversion is determined using two grades of silica nanoparticles of different hydrophobicities. Two oils of different viscosities are used to determine the effect of oil viscosity on phase inversion. The inversion point is detected by continuous measurement of the electrical conductivity of emulsions. With the increase in the concentration of hydrophobic nanoparticles in the oil phase, the phase-inversion concentration of water increases indicating a delay in inversion. The presence of hydrophilic nanoparticles in the oil phase promotes early inversion of W/O emulsion to O/W emulsion, especially at low nanoparticle concentrations. The hydrophilic nanoparticles tend to behave as hydrophobic nanoparticles at high concentrations resulting in a delay of phase inversion. The influence of oil viscosity on phase inversion of emulsions is stronger in emulsions prepared from hydrophobic nanoparticles. Based on the data generated in this work, emulsion state diagrams identifying regions of different emulsion morphologies (W/O or O/W) are developed.