Investigations on smectic X* and re-entrant smectic C* orderings in hydrogen bonded ferroelectric liquid crystals

Abstract

Two homologous series of hydrogen bonded ferroelectric liquid crystal (HBFLC) series have been isolated. One mole of ferroelectric Dextro tartaric acid (DTA) is mixed with 2 mol of p-n-alkyloxy benzoic acid (BAO) to obtain homologues of DTA + nBAO. Eight mesogens are isolated by varying the carbon number from pentyloxy to dodecyloxy viz., DTA + 5BAO to DTA + 12BAO. Similarly 1 mol of ferroelectric Dextro tartaric acid (DTA) is mixed with 2 mol of p-n- alkyl benzoic acid (BA) to obtain homologues of DTA + nBA. Seven mesogens are isolated by varying the carbon number from pentyl to dodecyl viz., DTA + 3BA to DTA + 8BA. Spectroscopic characterization (FTIR, 1H and 13CNMR) for all the 14 mesogens indicate the formation of hydrogen bond in HBFLC. Optical textures are recorded in various phases. An interesting observation is the finding of parachromatism in cholesteric phase. In addition to the conventional phases, two new smectic orderings viz., smectic X* and re-entrant smectic C* have been characterized. The textures of smectic X* exhibits a worm like textures while that of smectic C* is broken focal conic and the transition from smectic X* to re-entrant smectic C*. Smectic X* is observed to be sandwitched between cholestric and smectic C*. The x-ray study of smectic X* confirm it to be a smectic ordering. Measurments of tilt angle, light filtering and dielectric relaxation studies have been performed in this new smectic ordering. A new smectic ordering labeled as re-entrant smectic C* has been identified and characterized. Data of dielectric relaxation, magnitude of tilt angle in this phase confirm this phase is distinctly different from conventional smectic C*. Re entrant Smectic C* and Smectic X* are observed in higher homologues of DTA + nBAO where ‘n’ varies from 8 to 12.