Improving solubilization in microemulsions with additives. 1. The lipophilic linker role

Abstract

In this paper, we will show that the presence of some proper additive at or near the interface may considerably alter the solubilization properties of the surfactant. We have compared the microemulsification of a hydrocarbon oil and a polar oil of similar molar volume in different physicochemical environments containing nonionic surfactants with variable alkyl group length and poly(ethylene oxide) chain size. The length distributions on both hydrophilic and lipophilic groups result in fractionation phenomena with interesting effects on the solubilization. An anomalous behavior leads us to show that the presence of a lipophilic amphiphile may considerably improve the solubilization. The effect is studied with different additives. A model for the role of this additive, called the lipophilic linker, is proposed, and the experimental results are interpreted according to the location of the different species in the gradient of polarity that exists through the interfacial region.