Nonionic microemulsions with cyclic oils - Oil penetration, efficiency andmonomeric solubility

Phase diagrams of ternary H2O-cyclic oil-CiEj (alkyl-polyglycol ether) syst ems have been determined for cyclic oils such as cyclohexane, ethylbenzene and toluene, and mixtures of cyclohexane with toluene. In order to solubili zed these polar oils, the hydrophilic surfactants C10E6 and C10E8 were used . From precise volume measurements of the middle phase at the phase inversi on temperature (PIT), the monomeric solubility of the surfactant in oil was obtained, making it possible to quantify the fraction of surfactant in the internal interface of the bicontinuous microemulsion. Independent density measurements confirm the values for monomeric solubility from the phase dia grams. In toluene systems, in particular, comparatively large monomeric sol ubilities were found, a fact which is responsible for the observed ineffici ency of the CiEj surfactants in solubilizing aromatic oils. As an exercise in how to handle mixed oils, we demonstrate for the cyclohexane-toluene pai r how the three-phase body of the cyclohexane system gradually changes to t hat of the toluene system as a function of the oil-mixing ratio. The penetr ating nature of toluene is clearly visible from the quantitative analysis.