The anisotropic pseudo-potential for nematic liquid crystals

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Abstract
Analysis of the electron resonance spectrum of a paramagnetic probe, vanadyl acetylacetonate, dissolved in a nematic liquid crystal, yields the order for the probe, providing it moves rapidly. As Schwerdtfeger and Diehl have shown, in the absence of molecular motion the sample yields a polycrystalline spectrum and the intensities of the lines now depend on the anisotropic probability distribution function for the probe. The analysis of the angular dependence of the intensities is difficult, but does yield the probability distribution function from which the anisotropic pseudo-potential can be determined. The pseudo-potential for vanadyl acetylacetonate dissolved in a binary mixture of nematogens at - 50°C is mainly a result of repulsive forces. In contrast the pseudo-potential for the probe in a single component of the mixture at room temperature is determined by dispersion forces. This dramatic difference may result from the close proximity of molecules at - 50°C increasing the significance of repulsive forces in comparison to dispersion forces.