Influence of nanoparticle addition to Winsor surfactant microemulsion systems

The influence of adding negatively charged silica nanoparticles to multiphase Winsor microemulsion systems of cationic surfactant/alcohol cosurfactant is reported. It is found that the particles do not change the salt-induced progression of Winsor systems to any great extent, even when added at the same concentration as the surfactant. We find that all of the particles transfer from water where they originate to oil at all salt concentrations, although the distribution of surfactant between phases is unaffected. It is ascertained that alcohol addition renders particles more hydrophobic promoting this transfer. Emulsions prepared from the equilibrium microemulsion and excess phase(s) invert from oil-in-water to water-in-oil with increasing salt concentration, such that the continuous phase is the one containing the surfactant aggregates. Their stability to coalescence is extremely low, due to mainly the ultralow tensions at the oil–water interface. Particle addition does not alter the emulsion stability, implying that they are not adsorbed to drop interfaces.