Some remarks on coalescence in emulsions or foams

Intrinsic coalescence (corresponding to the opening of a hole in a surfactant monolayer) is important only for poor surfactants. With good surfactants, and in usual industrial conditions, coalescence is extrinsic, and mainly due to dirt particles. In the present note, we first analyze the motions of one dirt particle inside an initially monodisperse O/W emulsion. The particle remains trapped at the surface of a growing oil droplet, of size R(t) similar to t(1/3). If we now go to a very dilute system of dirt particles, we expect that they generate first a collection of large drops. Ultimately, these large drops come into contact, and one may end up with an oil matrix containing droplets of the O/W emulsion. (C) 2001 Elsevier Science Ltd. All rights reserved.