EFFECT OF MICROEMULSIFIED SURFACTANT IN DESTABILISING WATER-IN-OIL EMULSIONS CONTAINING C12E4

We have investigated microemulsion formation and emulsion stability in oil-water mixtures containing the non-ionic surfactant n-dodecyltetraoxyethylene glycol ether (C12E4). The oil component was either pure n-heptane or mixtures of heptane with a medium chainlength triglyceride (MCT). Equilibrium microemulsion droplet sizes, critical microemulsion concentrations (c.mu.c.) and post-c.mu.c. oil-water interfacial tensions are reported for water-in-oil (w/o) microemulsions present in equilibrium with excess water (Winsor II systems). The major effect of incorporation of MCT in these systems is to increase the c.mu.c. in the oil phase. Homogenisation of the two-phase Winsor II systems produces w/o macroemulsions in which the continuous oil phase is itself a w/o microemulsion. At surfactant concentrations higher than the c.mu.c., the main emulsion breakdown process is water drop sedimentation with concomitant oil phase separation. Maximum emulsion stability is found to occur at a surfactant concentration equal to the c.mu.c. for all the different systems. The rate of oil phase separation is accelerated by increasing the concentration of microemulsion droplets in the continuous phase of the emulsion. The accelerating effect was similar for different microemulsion droplet sizes. The experimental observations were found to be reasonably consistent with a depletion flocculation interaction of the emulsion drops.