A Study of Reentrant Smectic Ordering in Hydrogen Bonded Ferroelectric Dodecyloxy Benzoic Acid and Tartaric Acid Liquid Crystal

Abstract

A linear hydrogen bonded homologous liquid crystal series has been isolated with chiral ingredient as levo tartaric acid possessing two chiral carbons and non chiral mesogen as p-n-alkoxy benzoic acids. In the synthesized hydrogen bonded complexes the p-n-alkoxy benzoic acid moiety varied from pentyloxy to dodecyloxy with an exception of butyloxy and hexyloxy benzoic acids. Textural studies have been carried out by polarizing microscopic studies, (POM). Interestingly the phase sequences exhibited by odd and even complexes are strikingly different. In other words phase sequence of Nematic, smectic C*, F*, and G* is observed in the odd hydrogen bonded complexes while in addition to these phases the even counter parts exhibit a new type of phase sequence with smectic C* followed by pseudo smectic C* and reentrant smectic C* phases which are designated as Sm C*, Sm C _p *, and Sm C _r * phases respectively. A detailed DSC and dielectric studies confirmed the existence of the reentrant phase. We report a new phase which looks like a long worms and designated it as the pseudo smectic C _p *. Theoretical arguments are presented towards the existence of reentrant phenomenon. The magnitude and order of the optical pitch in this phase is almost identical to that of traditional smectic C* phase. Phase diagram is constructed for the homologous series. Results of tilt angle, dielectric relaxations and dielectric permittivity variations are discussed.

Keywords:

• Levo tartaric acid
• p-n-alkoxy benzoic acid
• pseudo smectic C_p*
• re-entrant smectic ordering

Acknowledgements

One of the authors (M. L. N. M. M.) acknowledges the financial support rendered by All India Council for Technical Education, Department of Science and Technology, and Defence Research Development Organization, New Delhi. Infrastructural support provided by Bannari Amman Institute of Technology is gratefully acknowledged.

Notes

^#Monotropic transition.

(c) cooling run.

(h) heating run.