Study of a magnetically oriented lyotropic mesophase

Abstract

A study of a magnetically oriented lyomesophase formed by a quaternary system (Na decyl sulfate/water/decanol/Na sulfate) is reported. Small angle x-ray diffraction measurements have been performed on unoriented samples and samples previously subjected to the action of magnetic fields (H). Diffraction patterns show a diffuse inner halo at 80–140 Å and a sharp outer ring at 38 Å. They reduce to spots in the equator for oriented samples with the x-ray beam parallel to H; no diffraction figure is produced for the x-ray beam perpendicular to H. NMR spectra indicate that the director of the phase orients perpendicular to H. These results show that this lyomesophase has a structure not previously encountered. A model of finite planar micelles surrounded by water is proposed. In this model the micelles consist of a bilayer in the form of platelets, probably disk shaped. These platelets align in presence of magnetic fields, with their plane parallel to H, and further orientational restrictions are imposed by the container; they tend to be parallel and some periodicity appears in the director of the direction of the phase, perpendicular to the plane of polar heads. The mesophase satisfies the definition for nematics taking into account periodicities induced in nematic phases by magnetic fields.