The average distances between micelles are measured by x-ray diffraction as a function of temperature in the discotic nematic phase of the lyotropic system comprised of potassium laurate 1-decanol, and ${\mathrm{D}}_2$O. The variations with temperature of the orientational order parameter are found to follow the variations of the shape anisotropy of the micelles, in good agreement with the microscopic models of the Onsager or Flory types.

• Received 12 February 1985

DOI:https://doi.org/10.1103/PhysRevA.31.4047