title: Direct measurement of contact angles of silica particles in relation to double inversion of pickering emulsions.
abstract: In an alkane-water system containing submicrometer silica particles at high pH, double emulsion inversion from oil-in-water (o/w) to water-in-oil (w/o) to oil-in-water can be effected by increasing the concentration of a dichain cationic surfactant in water. The contact angle θ of the particles at the planar oil-water interface has been measured directly using freeze-fracture shadow-casting cryo-scanning electron microscopy, enabling single-particle measurements of high accuracy. θ passes through a maximum with respect to surfactant concentration. It is shown that particles undergo a hydrophilic-hydrophobic-hydrophilic transition corresponding closely to the o/w-w/o-o/w transformation observed in emulsions. These results unequivocally link the single-particle contact angles to the type of particle-stabilized emulsion, confirming macroscopic emulsion inversion on the microscopic level.
authors.affiliation: Department of Chemistry, University of Hull, Hull, UK. b.p.binks@hull.ac.uk
authors.forename: Bernard Paul
authors.initials: BP
authors.lastname: Binks
authors.forename: Lucio
authors.initials: L
authors.lastname: Isa
authors.forename: Andrew Terhemen
authors.initials: AT
authors.lastname: Tyowua