Evidence for de Vries structure in a smectic-A liquid crystal observed by polarized Raman scattering -: art. no. 041705

The second- and fourth-order apparent orientational order parameters of the core part of the molecule < P-2 >(app) and < P-4 >(app), have been measured by polarized vibrational Raman spectroscopy for a homogeneously aligned ferroelectric smectic liquid crystal with three dimethyl siloxane groups in the achiral terminal chain, which shows de Vries-type phenomena, i.e., very large electroclinic effect in the smectic-A (Sm-A) phase and a negligible layer contraction at the phase transition between the Sm-A and Sm-C-* phases. The apparent orientational order parameters of the rigid core part of the molecule are extremely small both with and without the external electric field in Sm-A. These results provide evidence for the existence of the de Vries Sm-A phase, where the local molecular director is tilted at a large angle.