Structure and rheology during catastrophic phase inversion of Pickering emulsions stabilized with fumed silica particles

Abstract

Oil in water Pickering emulsions undergoing catastrophic phase inversion were investigated. Two polydimethylsiloxane (PDMS) oils of various viscosity have been emulsified in water and stabilized with fumed silica particles. The concentration of particles and the oil volume fraction were varied from 0.1 to 1 wt% and from 10 to 90 vol%, respectively. Upon increasing the oil content, a phase inversion occurred from oil-in-water to water-in-oil as evidenced from macroscopic and microscopic observations. At low concentration of particles, phase inversion occurred at lower oil volume fraction for the more viscous PDMS. Rheological measurements showed a strong increase of the elastic modulus of the emulsions with increasing the amount of oil up to a maximum value where the catastrophic phase inversion took place. The viscoelastic behaviour of the emulsions was discussed considering their structure but also the rheology of the particle suspensions that have been dispersed in both oil and water phases.