Influence of bias voltage on the orientation of core carbonyl and phenyl groups of a ferroelectric liquid crystal mixture studied by polarised FT-IR spectroscopy

Fourier Transform Infrared Spectroscopy is used to find the effect of the applied bias voltage on the orientational behaviour of core carbonyl (C=O) and phenyl ring (C-C) bands with stretching vibrations at 1737 cm(-1) and 1605 cm(-1), respectively, in a ferroelectric liquid crystal. Infrared measurements at normal incidence are carried out as a function of polarisation angle for which the bias voltage is altered across the cell. The effect of bias voltage on the dichroic ratio for phenyl ring is observed whereas carbonyl group is found not to exhibit dramatic variation in the dichroic parameter. The degree of orientation is expressed in terms of dichroic ratios as a function of bias voltage which shows a non symmetrical pattern for phenyl band as the polarity of the held is altered across the cell. It is also found that the polar angle (Omega(max)) between the smectic layer normal and the direction to absorbance maximum (A(max)) together with their absorbance profiles of both carbonyl and phenyl groups have asymmetrical rotations with respect to the polarisation axis as the polarity of the applied biased voltage is altered. The absorbance profiles of each stretching bands are quantitatively analysed and the rotational bias parameters of the azimuthal distribution function of the transition dipole moments related to the molecular core are calculated.