THE NATURE OF THE SMECTIC E PHASE

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Abstract
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

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