Stability of water-in-oil-in-water type globules

A method for producing a single water-in-oil-in-water (W/O/W) type globule is used to study its stability microscopically, by bringing the internal water droplets in contact with each other and with the external interface between water and oil. Each experiment lasted 24 h unless there was rupture within a shorter period, and the parameters that were studied are pH, ionic strength and the concentration of Span 80 surfactant. Under all experimental conditions that produced limited stability, the internal water droplets did not coalesce among themselves, and when the globule broke it was because the internal water droplets coalesced with the external phase. In the absence of surfactant the globule was found intrinsically unstable at all pHs and salinities. Experimental results are explained through a model for the interaction energy, van der Waals and Coulombic, between a single internal water droplet and the external aqueous phase as well as between two internal water droplets. A key parameter in the model is the 'effective thickness' of the adsorbed layer of surfactant, which determines whether the net interaction energy is attractive or repulsive. Copyright (C) 1996 Elsevier Science Ltd