An investigation of the fish diagrams of water or brine/decane or dodecane/propylene glycol ether (C3P1 or C3P2) systems

Abstract

In this study, liquid–liquid equilibrium measurements were performed for different ternary, water (or brine)/decane or dodecane/mono-propylene glycol ether (C3P1) or di-propylene glycol ether (C3P2) systems in order to build the so-called fish phase diagrams (temperature as a function of surfactant for a given polar-apolar solvent mixture) and to compare them to the well-known water (or brine)/decane or dodecane/ethylene glycol mono-butyl ether (C4E1) phase diagrams. The study is motivated by the lower toxicity of the CxPy compared to the corresponding CxEy. Toxicity is of particular importance for any use of such molecules in the environment. Like in the presence of C4E1, the formation of Winsor type I→III→II phase transitions with increasing temperature was observed for the CxPy systems. The LCST (Lower Critical Solution Temperature) and UCST (Upper Critical Solution Temperature) of the newly studied systems were determined. The values of the γ0 parameter (in mole fraction), the minimum value of surfactant needed to form Winsor III, increased in comparison to the C4E1 systems. The value of γ˜ (in mole fraction), minimum value of surfactant needed to reach Winsor IV from Winsor III, was comparable using C4E1 and C3P1, and lower in the presence of C3P2. The substitution of decane by dodecane led to a stronger water affinity of C4E1 and C3P2 as greater values of the LCST and UCST have been observed in the presence of dodecane. By contrast, a lower hydration of C4E1 and C3P1 was found when increasing the NaCl content in brine. It can be concluded that less toxic C3P1 and C3P2 can be envisaged as a substitute of the contested C4E1 to formulate microemulsions and particularly Winsor III systems.