Rheology and structure of Pickering emulsions undergoing transitional phase inversion using a mixture of hydrophilic and hydrophobic silica particles

We investigate the stability and the structure of Polydimethylsiloxane (PDMS)/water emulsions stabilized by a mixture of partially hydrophobic (Aerosil® R816) and hydrophilic silica particles (LUDOX TM 50). Transitional phase inversion from oil-in-water (O/W) to water-in-oil (W/O) is observed by changing the hydrophobic/hydrophilic particles ratio as well as the viscosity of the oil phase. A higher concentration of hydrophilic particles is needed to promote phase inversion for the less viscous oil. Adding gradually hydrophilic silica particles in the water phase leads to the decrease of the fraction of effective emulsified phase i.e. the dispersed phase and the increase of the droplet size which promotes the phase inversion. In addition, all these changes are accompanied by the decrease of the elastic moduli of the emulsions which may be correlated to their complex structure and the interactions of the two types of particles at the interface of the droplets.