Abstract
The W + D + O three-phase region is observed in water/nonionic surfactant/hydrocarbon systems over a wide range of water/oil ratios at very low surfactant concentrations. With amphiphilic oils such as long-chain alcohols, fatty acids, monoglycerides, or triglycerides, the phase behavior is quite different; W + D′ + O m- and W + LC + O-type three-phase regions are observed, where W and O are excess water and oil phases, O m is the nonaqueous reversed micellar solution phase, LC is the lamellar liquid crystal, and D and D′ are surfactant phases. When an amphiphilic oil is added to a water/nonionic surfactant/hydrocarbon system, the LC and D′ phases intrude into the W + D + O three-phase region which in turn splits into two parts. As the concentration of amphiphilic oil increases, the intruded part becomes wider; eventually the W + D + O region disappears; the W + D′ + O m and the W + LC + O regions remain in a water/nonionic surfactant/amphiphilic oil system. Consequently, four coexisting isotropic phases (W + D′ + D + O) appear when the W + D + O region in a water/nonionic surfactant/hydrocarbon system is interacted and overlapped with a W + D′ + O m region in a water/nonionic surfactant/amphiphilic oil system. The phase behavior of nonionic surfactant and ionic surfactant systems is also delineated.
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