Capillary Pressure in Thinning Emulsion Film Stabilized with Solid Spherical Particles

Abstract

Stability and coalescence of emulsions stabilized with solid particles is determined by the energy of particle “attachment” at the liquid–liquid interface (the energy of adhesion) and by the value of capillary pressure arising in the emulsion film in the process of its thinning under the lower pressure when two layers of solid particles (on the opposite film sides) draw together up to their direct contact and formation of menicsi in the porous space between particles. We calculated maximal (critical) capillary pressure P _{c, max} whose exceeding leads to the film rupture as a function of contact angle and the size of solid particles needed to form the “adsorption” layer of monodisperse spherical particles with a dense hexagonal packing. Capillary pressure isotherms P _c(h) (h is the thickness of emulsion film) were also calculated. The deviation of meniscus shape from spherical was considered using the Mayer, Stowe, and Princen method. Determination of capillary pressure in a model emulsion film containing hexagonal-packed transparent glass spheres demonstrated that, at various degrees of particle hydrophobicity, experimental data are in good agreement with theoretical calculations of the P _{c, max} value and P _c(h) isotherm.