INTERFACIAL SEGREGATION OF AN ETHYL OLEATE HEXADECANE OIL MIXTURE IN MICROEMULSION SYSTEMS

The phase behavior and optimum formulation of systems containing comme rcial polyethoxylated octylphenol surfactant, water, and a mixture of ethyl oleate and hexadecane exhibit variations which may be interprete d by two phenomena: first the partitioning and fractionation of the su rfactant species between the different phases, which is found to depen d significantly upon the polarity of the oil phase. By taking into acc ount these effects, the interfacial or real formulation can be compute d, and a second phenomenon is found, i.e., the segregation of the oil near the interface. The interfacial oil layer segregation has been exp erimentally put in evidence for the first time through the oil partiti oning-fractionation phenomena which occur in low solubilization off-op timum systems containing slightly, swollen micelles. The experimental evidence supports a model in which the oil layer located next to the i nterface contains more ethyl oleate than the bulk oil phase. At and be yond 50 mol % ethyl oleate in the oil mixture with hexadecane, the int erfacial oil behaves as if it were essentially composed of pure ethyl oleate, with an equivalent alkane carbon number (EACN) estimated at 6, a clear hint of its polarity.