Deviations from the spontaneous curvature in surfactant films : effects on the second virial coefficient and interfacial properties of the microemulsions

Publisher Website
Google Scholar
Abstract
One evaluates the contributions of the surfactant interfacial film bending energy first to the attractive interactions between droplets in dilute microemulsions and second to the interfacial tensions in triphasic Winsor systems far from the critical points. (1) In a dilute water in oil microemulsion where the water droplet curvature (defined as positive) is slightly larger than the interfacial film's spontaneous curvature C0, a possible fluctuation at thermodynamic equilibrium is the fusion of two droplets in a dimer of low curvature energy. This process gives an attractive contribution to the droplet second virial coefficient which is in good agreement with certain experimental observations. (2) The interface between a microemulsion and an excess phase, oil for example, is either closed by a flat Langmuir type surfactant film, in which case a wetting water layer separates the film and the microemulsion, or open, i.e. traversed by oil pores. The microemulsion surfactant film curvature is on average directed towards oil in the first case and towards water in the second case. We show by using the microemulsion random structure model proposed by de Gennes that, in the Winsor triphasic systems, the water/microemulsion interface evolves from the case « open » to the case « closed » and the oil/microemulsion from the case « closed » to the case « open », when the water salinity, i.e. C0, increases. When | C0 | is small, the two interfaces are « open » and the difference between the surface tensions of the two interfaces is proportional to C0. One recovers the result that this difference vanishes at the optimal salinity (C0 = 0)

This publication has 19 references indexed in Scilit: