J. Phys. Colloques
Volume 37, Numéro C3, Juin 1976EXPOSÉS et COMMUNICATIONS présentés à la Conférence Européenne sur Les Smectiques Thermotropes et leurs Applications / European Conference on Thermotropic Smectics and their Applications
|Page(s)||C3-65 - C3-68|
J. Phys. Colloques 37 (1976) C3-65-C3-68
THE NATURE OF THE SMECTIC E PHASEA. J. LEADBETTER1, R. M. RICHARDSON1 and C. J. CARLILE2
1 Chemistry Department, University of Exeter, Exeter. EX4 4QD, U. K.
2 Neutron Beam Research Unit, Rutherford Laboratory, Chilton, Oxon. OX11 OQX. U. K. and ILL, 38-Grenoble, France
Incoherent neutron scattering experiments have been carried out on a powder sample of D-PBABC ([MATH] [MATH]CH=N[MATH]CH=CH COOC4D9 : Crystal 77 °C SE 107 °C SB 172 °C SA 206 °C Isotropic Liquid ) in the smectic E phase at 92 °C and 60 °C (supercooled) and in the crystalline phase at 60 °C. Data were obtained for 0.16 <≈ Q/Å-1 <≈ 1.14 with a resolution of 28 µeV (FWHM) on a time-of-flight spectrometer at ILL Grenoble. No molecular motion is observed in the solid phase showing that any relaxations are slower than ~ 0.5 GHz. Molecular motions are observed in the smectic E phase and the results have been compared with models of reorientational motion about the long molecular axes. It is concluded that some restricted rotational motion occurs with a correlation time of a few GHz-1. The nature of the rotational motion is not yet established but appears to involve two-fold reorientation through an angle π and the restriction in the motion involves either part of the molecule rotating more slowly than the rest, or a preferred orientation of the molecule as a whole (on the neutron time-scale), or both.