Orientational Characteristics ofnCB(n=5,6,7) Liquid Crystals by Means of Fluorescence Probe Method

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Abstract
Three kinds of fluorescence depolarization ratios (R 1, R 2 and R 3) of 4-amino-4′-nitrobiphenyl have been measured in the b'quid crystalline state of 5CB, 6CB and 7CB. It was found that these three ratios depend to a certain extent on the sample thicknesses. The dependence was studied in detail by using three kinds of cells of different thickness for each sample. The 2nd orientational order parameter P 2, evaluated analytically from R 1, R 2 and R 3 were found to be thickness independent. Several methods to estimate the fourth orientational order parameter P 4 of the solute from the above P 2 or from that of a neat sample were examined on the basis of Marcelja's type mean field theory. The temperature dependence of two correlation times of rotational Brownian motion have been evaluated and interpreted on the basis of a reorientational diffusion model.