Dispersion of proton spin-lattice relaxation in a cholesteric liquid crystal

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Abstract
The frequency and temperature dependence of T1and T1ρ in the cholesteric and isotropic phases of cholesteryl-oleyl-carbonate (COC) have been determined together with the temperature dependence of the self-diffusion constant D in the isotropic phase. In the MHz region the relaxation is dominated by molecular self-diffusion — with D being of the order 10-12 m2/s — and by local molecular rotations with τc ~ 2 x 10-10 s at T = 24 °C. In the kHz region, on the other hand, order director fluctuations predominantly influence the relaxation. The influence upon T 1ρ of the rotation of the molecules caused by their diffusion along the helix, an effect occurring only for twisted structures, was not observed in COC in view of too long a rotational correlation time