Internal Dynamics of Flexible Mesogens

Abstract

In Chapter 4, the effects of internal motion on averaging the local spin interaction tensors to give spectral splittings and/or shifts in NMR spectra of liquid crystals were considered. The analysis of dynamical properties in molecular systems with many degrees of freedom is more complex than that of the equilibrium properties. Spin relaxation characteristics of nuclear spin systems are influenced by internal degrees of freedom within spin-bearing molecules. Although internal rotations about C-C bonds in macromolecules dissolved in solution have been studied, both theoretically and experimentally, since the 1970s [8.1-8.6], the task of formulating spin relaxation theories for liquid crystals is just beginning and is a formidable one. Drastic assumptions are made in order to simplify the treatment of many internal degrees of freedom in mesogens reorienting in anisotropic mesophases. Only when sufficient spectral parameters are obtained from relaxation behaviors of nuclei like 13C and 2H can there be hope of checking or removing some of the crude assumptions used in the spin relaxation theory. In spite of the limitations in these relaxation theories, there is evidence that NMR can reveal information not available from other techniques.KeywordsLiquid CrystalSpectral DensityInternal DynamicsInternal MotionRotational DiffusionThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.