Flexibility, persistence length and bicontinuous microstructures in microemulsions

Three length scales have to be considered to describe microemulsions: persistence length, spontaneous radius of curvature of the surfactant film as intensive variables and finally the characteristic size imposed by the ratio of volume fraction to available specific area surface. The specific area per unit volume is an intensive variable linked to sizes and topologies that can be built without tearing the surfactant film. We show here that at least four types of bicontinuous microstructures have been detected so far, and that they can be distinguished by a simple experimental determination of the evolution of scattering peak position versus dilution. Besides the classical microstructures dominated by entropy or a priori considered as droplets, the other microstructures identified so far can be approximated as connected cylinders or randomly connected swollen bilayers. All these microstructures can be considered as "molten" precursors of the lyotropic liquid crystalline phases that are adjacent to microemulsions in phase diagrams. To cite this article: T Zemb, C R. Chimie 12 (2009). (C) 2008 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.