Random Torsional Oscillation Model for Rotational Molecular Motion. Cold Neutron Scattering Investigation of Cholesteryl Propionate, Nonanoate, and Myristate

Abstract

AbstractThe incoherent scattering function for the case of simple translation of the centre of mass and the random torsional oscillations of the rigid planar body along the long molecular axes of an amplitude φ of perfectly ordered molecules in nematic phase, is calculated. The model of a random molecular torsional motion is built on the assumption that each proton in the molecule suffers a large number of equal angular displacements between two perfectly reflecting barriers at φ and −φ. The dynamics of molecular tail is described by uniaxial free rotational diffusion and freely rotating spherical top models, respectively. The predictions of the calculations are tested on measured time of flight spectra, obtained on three members of a homologous series of cholesteric liquid crystals and agreement is obtained.