A comparative study of the molecular motions in the three smectic phases of isobutyl 4(4′ phenylbenzylideneamino) cinnamate using incoherent neutron scattering

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Abstract
Incoherent quasi-elastic neutron scattering results from aligned samples of isobutyl 4(4′ phenylbenzylideneamino) cinnamate in its smectic E, B and A phases are presented. The main results of a detailed analysis in conjunction with results from other techniques are as follows. Translational diffusion parallel to the layer normal is hindered in the SA phase by a weak temperature dependent barrier (5 to 15 kJ mol-1) but this is much stronger in the SB and SE phase (at least 30 kJ mol-1). However a feature of all three phases is that the molecules have the freedom to move diffusively on a time scale of 10-11 s by ∼ 1–4 Å parallel to the layer normal. The molecules appear to undergo uniaxial rotational diffusion about their long axes in the SA and SB phases although it is not possible to discount some weak orientational ordering into six equivalent sites in the SB . In the SE phase there is a clear onset of orientational ordering into two sites separated by π. Dynamic fluctuation of the long molecular axes occur on the same time scale as the rotation about the long axes in the SA phase (τ ∼ 2 × 10-11 s) but their amplitude drops and their correlation time increases by an order of magnitude in the SB .

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