Osmotic Stabilization of Concentrated Emulsions and Foams

Abstract

In the absence of coalescence, coarsening of emulsions (and foams) is controlled by molecular diffusion of the dispersed-phase species from one emulsion droplet (or foam bubble) to another. Previous studies of dilute emulsions have shown how the osmotic pressure of a trapped species within droplets can overcome the Laplace pressure differences that drive coarsening, and “osmotically stabilize” the emulsion. Webster and Cates (Langmuir 1998, 14, 2068−2079) gave rigorous criteria for osmotic stabilization of mono- and polydisperse emulsions, in the dilute regime. We consider here whether analogous criteria exist for the osmotic stabilization of mono- and polydisperse concentrated emulsions and foams. We argue that in such systems the pressure differences driving coarsening are small compared to the mean Laplace pressure. This is confirmed for a monodisperse 2D model, for which an exact calculation gives the pressure in bubble i as Pi = P + Π + PiG, with P the atmospheric pressure, Π the osmotic pressure, an...