Alkyl chain motions in columnar mesophases

Abstract

The dynamical behaviour of the alkyl chains in dicopper tetrapalmitate is investigated in the columnar liquid crystal phase, using incoherent quasielastic neutron scattering by several selectively deuterated derivatives. A mathematical model is developed for the evaluation of the scattering function which yields the free volume accessible to each hydrogen atom along the chains, approximated by a sphere. It is shown that the hydrogen atoms linked to the carbons close to the core undergo very little motion. The radius of the spheres is a nearly linear function of the distance from the core between the first and the fifth carbons and then reaches a limiting value directly related to the spacing between the stacked molecules. These results were fully confirmed by the analysis of the overall quasielastic broadening of the spectra as a function of the momentum transfer.