Phase behaviour and structure in a non-ionic surfactant–oil–water mixture

Abstract

A section of t h e composition-temperature phase prism of a ternary non-ionic surfactant-water-oil system defined by a constant surfactant to oil ratio has been investigated. The structural sequence of normal spheres to planar bilayers, via cylinders, is observed a s a function of decreasing water concentration at fixed temperature.As a function of increasing temperature at fixed surfactant and oil concentration, we note the commonly observed reversal in mean curvature of the polar/apolar interface. The mean curvature progressively alters from positive values in t h e low-temperature microemulsion phase to negative mean curvature in t h e hightemperature L, phase, with an intermediate lamellar phase where t h e mean curvature passes through zero. The phase diagram of this section is similar to that of, the binary surfactant-water system. The average area per surfactant at the polar/apolar interface is 46 & 2 A2. A micellar cubic phase is observed between t h e microemulsion and the hexagonal phase while no bicontinuous cubic phase is observed.

Curvature elasticity of thin films

“…Measurements of the drop size along the phase boundary for the coexistence of nearly spherical microemulsion drops with excess internal phase (oil) in non-ionic systems [65] indicates that the spontaneous curvature varies linearly with temperature in this regime. For these systems, it appears that corrections to the linear phase boundary due to entropy of mixing e ects are small.…”

Ionic Liquids in Microemulsions—A Concept To Extend the Conventional Thermal Stability Range of Microemulsions

“…Basic prerequisite for studying the properties of such microemulsions is knowledge of their phase behavior as it depends on several parameters, such as temperature, pressure and the nature of the components. Probably one of the most important variables in non-ionic microemulsions is temperature, 91 while the effect of pressure has turned out to be rather weak. 92 The molecular origin of the strong temperature dependence of the phase behavior of C i E j containing system is related to the interaction between water and the oligo(ethylene oxide)…”

Characteristics of spontaneously formed nanoemulsions in octane/AOT/brine systems

“…However, IFT is so low in this case that the effect of curvature (droplet radius) on octane solubility in brine may no longer be the main driving force. Other data on small droplet growth in microemulsion systems have been interpreted in terms of variation of curvature elastic energy of interfacial surfactant films with drop radius [71]. The presence of the lamellar phase, as discussed next, could also influence growth rates.…”