CRITICAL STUDIES OF MOLECULAR REORIENTATION IN ORIENTED PAA WITH VARIOUS KINDS OF DEUTERATION

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Abstract
Quasielastic neutron scattering experiments carried out for nematic d6-PAA and d8-PAA were analysed by using the rotational diffusion around the long molecular axis model. The τ1 rotational correlation time was estimated for a 4 ps. This value does not agree with the dielectric relaxation time which equals to 20 ps. Such disagreement may be a reflection of differences in the type of response : the neutron method leads to a monomolecular response, whereas dielectric measurements reflect bulk properties. On the other hand the above disagreement may be an indication that the model of rotational diffusion is too simple. A few conclusions concerning the translatory diffusion in PAA, and also the methyl groups rotation are made

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