INVESTIGATION OF RESTRICTED MOLECULAR-REORIENTATION IN MBBA IN THE NEMATIC PHASE BY QUASI-ELASTIC INCOHERENT NEUTRON-SCATTERING

Neutron incoherent quasielastic scattering experiments on the liquid crystal MBBA in the nematic phase are reported. Taking advantage of published NMR results it is shown that the motion of an oriented MBBA molecule is composed of two parts. The 12 protons of the butyl end and alkoxy chains perform uniaxial rotational diffusion with a diffusion constant of 10(10) s-1 while the 9 protons of the rigid benzylideneaniline core are restricted to a uniaxial simple rotational diffusion on a segment of a circle of an apex angle of 57-degrees with an associated rate constant of 2.3 x 10(10) s-1.