The effects of Heisenberg spin exchange on the linewidths of the nitroxide free radical di-tert-butyl nitroxide (DTBN) in the nematic liquid crystal N-(p-Methoxybenzylidene)-p-butylaniline (MBBA) have been measured as a function of the temperature and concentration of the free radical. At higher temperatures (>20°C) the spectra are analyzed in terms of spin exchange interactions using Freed's formalism, modified to take into account the anisotropic nature of the viscosity of the liquid crystal. At lower temperatures (< 20°C) it is observed that magnetic dipole-dipole interactions between partially oriented DTBN molecules becomes important.
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Bales et al. (1974) studied this question.
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