Molecular motions in liquid crystal BBBA (4O.4): QENS study

Molecular rotational motions in butyloxybenzylidine butylanilene as studied by quasielastic neutron scattering technique in the smectic B and smectic A phases are reported. The end chain (butyl group) and the core of the liqu id crystal are found to undergo rotational motions, independent of each oth er. Both of these are best described by the jump rotation, with N = 12 equi valent sites on a circle or uniaxial rotational diffusion. Reorientation ti mes, tau (1), equal to 6.1 x 10(-11) +/- 1.6 x 10(-11) and 1.8 x 10(-11) +/ - 0.6 x 10(-11) s are obtained for the core group and end chain, respective ly, in the smectic B phase. The geometry of rotation has been found to be u nchanged in the smectic A phase and the corresponding reorientation times e qual to 4.1 x 10(-11) +/- 1.2 x 10(-11) and 1.6 x 10(-11) +/- 0.5 x 10(-11) s, respectively, are obtained. (C) 2000 Elsevier Science B.V. All rights r eserved.