Phase behavior of octyldimethyl para-amino benzoate, polyoxyethylene-10-stearyl ether, olive oil, and water

The phase diagrams of octyl dimethyl para-amino benzoate (ODP)/polyoxyethylene-10-stearyl ether (Steareth 10)/olive oil/water, and of ODP/polyoxyethylene-4-lauryl ether (Laureth 4)/water systems were determined. ODP was solubilized in the lamellar liquid crystal of Steareth 10 water and of Laureth 4 water to 15 and 12% by weight, respectively. Low-angle x-ray diffraction was used to determine the location of the ODP molecules in the liquid crystal. ODP penetrated between the hydrocarbon chains of the surfactants, while olive oil was solubilized both at that site and between the terminal methyl group layers. The location of ODP in the liquid crystal was also reflected in ultraviolet absorption in the 260-350 nm region of the spectrum, which was compared to absorption in a polar solvent, polyethylene glycol (260-340 nm), and in a nonpolar solvent, decane (260-328 nm).