Study of the molecular tilt angle and the order parameter of a ferroelectric liquid crystal mixture using IR spectroscopy

We report measurements of the molecular tilt angle of a ferroelectric liquid crystal mixture (ZLI 3654), using infra-red spectroscopy, and of the optical tilt angle using polarizing microscopy. The molecular tilt angle is found to be approximately the same for different molecular vibrations. The second rank orientational order parameter for the axis of molecular vibrations of different groups of the molecule for homogeneously aligned samples have been determined as a function of temperature. The order parameter depends slightly on the sample thickness and is about 8 per cent higher for a lower thickness (∼ 7 μm) compared to a higher thickness (∼ 12 μm). The order parameter does not change significantly at the S_C*-S_A transition. The order parameter of S_C* is found to be unaffected by the application of a constant electric field. The order parameter for the alkyl chain is found to be about three times lower than for the molecular core.