A Global Description of Phase Equilibria in the Quaternary Microemulsion System: Water-Dodecane-Pentanol-Sodium Dodecylsulfate

Abstract

The knowledge of the phase diagram of a multicomponent system is a fundamental necessary step for the understanding of the physics of the system. It has been clearly and intensively shown by Ekwall and coworkers[1] that phase equilibria in multicomponent aqueous mixtures of amphiphilic molecules can be richly diverse and intricate. Due to their considerable potential for aggregation the surfactant solutions show a multiplicity of structures (bilayers, cylinders, spherical micelles) which can organize and produce a great variety of isotropic and mesomorphic phases. The phase diagrams of several water-surfactant-alcohol and watersurfactant-oil mixtures have been investigated in detail [1–6]. They display a rich variety of phases and also complex multiphase regions where two or three liquid isotropic and mesomorphic phases are in equilibrium. As we will see later in this paper, the phase diagrams of the quaternary mixtures which give rise to microemulsion phases are not qualitatively different from those of ternary mixtures described by P. Ekwall. One still encounters ordered phases but their extent is considerably reduced. Generally mesomorphic regions are replaced over a broad domain of water and oil concentrations by an isotropic liquid microemulsion phase where no long range order occurs.