Pressure-induced reduction of the Landau-Peierls instabilities in a side-chain polymer liquid crystal with reentrant polymorphism.
Cyanobiphenyl mesogens are known to exhibit partially bilayered smectic A (S(Ad)) and also reentrant nematic (N(re)) phases. Nematic and smectic orders are coupled parameters which depend both on temperature and pressure. We report the first structural study of the influence of a hydrostatic pressure on the smectic phase. This study was carried out on a side-chain liquid crystalline polymer, by neutron diffraction using two specifically designed pressure cells. These results concluded first that the pressure acts on the phase elastic constants via a reduction of the layer fluctuations giving rise to a hardening of the phase together with an extension of the smectic domain towards higher temperatures. Second, the S(Ad)-N(re) phase transition temperature remains unchanged in the studied pressure range revealing that the polymer component plays an important role which allows us to subtract the associated packing interactions from the pressure-induced volume reduction.
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Laboratoire Léon Brillouin (CEA-CNRS), CE Saclay, 91191 Gif-sur-Yvette Cedex, France.
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