Variation of Absorbance and Helical Unwinding with Electric Field in an Antiferroelectric Liquid Crystal Using Polarized FT-IR Measurements

Abstract

For a homogeneously aligned cell of an antiferroelectric liquid crystal, infrared spectra have been recorded for SmC*, SmC_γ* and SmC_A* phases. To investigate the characteristics of absorbance peak and helical structure for each smectic phase, the rotation of the absorbance profiles for phenyl, core carbonyl and chiral carbonyl groups are studied as a function of polarizer angle at various stages of electrically induced transformation of the sample structure. It is found that, the absorbance profile for both the phenyl and the carbonyl groups for the three smectic phases have the same rotational motion for the same polarity of the applied field to the cell. The maximum rotational angle for the absorbance profile of phenyl group for each phase is obtained when the helix structure is completely transformed to an unwound SmC* phase. It is observed that, the helix is already disturbed before the application of electric field to the cell for each molecular group. The results of the measurements are studied in detail and the variation of maximal absorbance in relation to helix unwinding behavior for a surface stabilized cell for each smectic phase is discussed.

Keywords:

• Antiferroelectric liquid crystal
• FTIR spectroscopy
• helical unwinding

Acknowledgement

We thank Dr. O. Kalinovskaya for her assistance in using electro-optic devices. Prof. A. Kocot and Dr. Y. Panarin are thanked for discussions.