Transverse deuteron spin relaxation in thermotropic liquid crystal polymers: determination of viscoelastic properties

Abstract

Transverse deuteron spin relaxation times, T CP 2E, from quadrupole echo pulse trains have been measured as a function of pulse spacing, τ, for a thermotropic liquid crystal polymer and dimer in the nematic phase. The relaxation times exhibit a dispersion law, T CP 2E∼τ − 1 2 , consistent with director fluctuations providing the dominant transverse relaxation process. The observed anisotropy in T CP 2E measured as a function of orientation, θ N , for the polymer approximately follows the (sin 2θ N cos 2θ N ) −1 dependence characteristic of this type of low-amplitude motion. Analysis of the experiments is achieved employing a simple hydrodynamic model for director fluctuations, yielding values for the effective viscosity and average elastic constant of the liquid crystal polymer and dimer.