Alkyl chain motions in columnar mesophases

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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.