Shape transformations of the aggregates in dilute surfactant solutions : a small-angle neutron scattering study

Abstract

The brine rich corner of the phase diagrams of quasitemary (surfactant/alcohol/brine) systems shows the domains of stability of three different phases : the classical micellar phase L1, the highly swollen lamellar phase L α and an isotropic phase with quite special physical properties herein denoted L2*. The successive phase transformations are triggered by increasing values of the alcohol/surfactant ratio. We here report an extensive small angle neutron scattering investigation of the morphological transformations of the aggregates all along the phase sequence. The following shape sequence is unambiguously evidenced : globules, rods and finally wide bilayers. The primary structures have the same morphology at a local scale (bilayers) in both the Lα and L2* phases. Only the large scale arrangement of this elementary object changes from L α to L2*. The very low q scattering patterns of L 2* suggest that the structure of this phase has a bicontinuous topology where the infinite bilayer separates two infinite interwoven equivalent self-connected brine domains.