Optical, thermal and electrical investigations in two homologous series of hydrogen bonded ferroelectric liquid crystals

Abstract

Two novel series of complimentary hydrogen bonded ferroelectric liquid crystals (HBFLC) comprising of 14 mesogens are synthesised by mixing (R)-(+)-2-(Benzyloxy) propionic acid (BPA) with various alkyloxy/alkyl benzoic acids. First series yielded eight HBFLC mesogens namely (R)-(+)-2-(Benzyloxy) propionic acid mixing with various benzoic acids viz., pentyloxy benzoic acid (BPA + 5BAO), hexyloxy benzoic acid (BPA + 6BAO), heptyloxy benzoic acid (BPA + 7BAO), octyloxy benzoic acid (BPA + 8BAO), nonyloxy benzoic acid (BPA + 9BAO), decyloxy benzoic acid (BPA + 10BAO), undecyloxy benzoic acid (BPA + 11BAO) and dodecyloxy benzoic acid (BPA + 12BAO) respectively. The second series yielded six HBFLC mesogens namely (R)-(+)-2-(Benzyloxy)propionic acid mixing with various benzoic acids viz., propyl benzoic acid (BPA + 3BA), butyl benzoic acid (BPA + 4BA), pentyl benzoic acid (BPA + 5BA), hexyl benzoic acid (BPA + 6BA), heptyl benzoic acid (BPA + 7BA) and octyl benzoic acid (BPA + 8BA) respectively. The molecular structure of entire 14 mesogens is represented by ball and stick model. Phase identification is made by textural studies of various phases through Polarizing Optical Microscopy (POM), enthalpy values and phase transition temperatures are elucidated from Differential Scanning Calorimetry (DSC) studies. The homologues of the first series BPA + nBAO exhibited smectic B*and smectic G* phases while only smectic G* phase is observed in BPA + nBA. Formation of hydrogen bond in the synthesised mesogens is confirmed by FTIR spectra. Phase diagrams for both the series are constructed from POM and DSC studies. Dielectric relaxation studies in smectic B* and smectic G* phases are performed on selected mesogens.

Keywords:

• (R)-(+)-2-(Benzyloxy) propionic acid
• alkyloxy/alkyl benzoic acids
• POM
• DSC
• FTIR

Acknowledgements

Eternal blessings of Bannari Amman and Infrastructural support provided by Bannari Amman Institute of Technology are gratefully acknowledged. The authors also acknowledge Science and Engineering Research Board, Department of Science and Technology, Government of India for their financial support (EMR/2017/001075).