Shape Changes of Globules in Nonionic Microemulsions

Abstract

Assuming the globules at the (lower) stability limit of (diluted) nonionic o/w microemulsions in the water-rich corner of the phase prism to be spherical, and assuming, furthermore, the mean curvature of the (saturated) interfacial layers to decrease monotonically with rising temperature, it is shown that the size distribution of the globules must change to a lower number density of larger nonspherical globules upon raising temperature at fixed mean composition simply for volumetric reasons, irrespective of the explicit expression for the temperature dependence of the mean curvature. Applying Flory's model, it is, furthermore, shown that this could explain the phase separation of o/w microemulsions at their upper stability limit in the water-rich corner. The same holds for w/o microemulsions in the oil-rich corner if the mean curvature is assumed to decrease with dropping temperature. The results are compared with the features of the phase behavior, and some experiments.