Orientational Distribution Function in Nematic Tobacco-Mosaic-Virus Liquid Crystals Measured by X-Ray Diffraction

Orientational distributions of the rod-shaped tobacco-mosaic-virus particle in magnetically aligned nematic solutions ($0.05M$ borate buffer, pH 8.5) were measured by analysis of the angular spread of x-ray diffraction patterns. We measured Gaussian orientational distributions with order parameters varying between 0.77 in a solution with coexisting nematic and isotropic phase, to 0.95 in the single-phase nematic solution at higher concentration. Our experimental results are in good agreement with model calculations based on a modified Onsager theory for suspensions of hard rods.