Microscopy and Deuterium NMR Studies on Induced Cholesteric Lyotropic Mesophases of Potassium Laurate

Abstract

Induced cholesteric lyotropic mesophases can be formed by the addition of cholesterol to “nematic” phases of potassium laurate/n-decanol/water and electrolyte. The resulting mesophases are oriented by magnetic fields, the helicoidal axes being collinear with the field (type II)or perpendicular to it(type I). In the present work, the textures of oriented cholesteric samples were examined under the polarizing microscope. The associated patterns depended on the mesophase type and on the applied field direction. The usual chevron and focal-conic textures were seen in type II cholesteric mesophases. More complex disclinations were exhibited by type I cholesteric phases. The comparison between the relative order profiles for type I and type II mesophases, nematic and cholesteric, obtained by deuterium NMR, shows that great distortions are not present in the micelles of the cholesteric systems. The overall picture suggests that mainly electrostatic interactions are responsible for the cholesteric properties in induced mesophases.