Phase behavior of the surfactant ionic liquid trihexyltetradecylphosphonium bis(2,4,4-trimethylpentyl)phosphinate with water and dodecane

Abstract Trihexyltetradecylphosphonium bis(2,4,4-trimethylpentyl)phosphinate is a surface-active room temperature ionic liquid: it is an ionic component, liquid at room temperature, and also a surfactant due to the presence of large (hydrophobic) alkyl chains attached to an ionic moiety. Moreover, since both the anion and the cation have large alkyl chains, both ions have surface active character, what has been called a catanionic or biamphiphillic surfactant. In this work, the surfactant has been characterized through the measurement of the critical micelle concentration in aqueous solutions and related parameters. The phase diagram for ternary mixtures with water and n -dodecane has been determined, showing a Winsor type III behavior. The effect of temperature and amphiphile concentration on the ternary system has been studied with fish diagrams. A large effect of temperature on the phase diagram has been found, with the existence of a triphasic region from 278 up to 305 K. Interfacial tension between equilibrium phases has been measured experimentally for the ternary system, using either pure water or 4 wt% NaCl brine. Density and viscosity of the involved phases have also been measured as valuable information in oil recovery. Results obtained are discussed in terms of the validity of this surfactant for this application.