Abstract
Calamitic liquid crystalline dimer containing azobenzene moiety and a decyloxy biphenyl linked by flexible spacers {4-[7-(4′-decyloxy-biphenyl-4-yloxy)-alkyloxy]-phenyl}-(4-decyl-phenyl)-diazene has been synthesized and characterized by spectroscopic methods. The transition temperatures and phase behaviours were studied by Differential Scanning Calorimeter (DSC) and Polarizing Optical Microscope (POM). The synthesized compounds exhibited enantiotropic liquid crystal phase with higher spacer display nematic and smectic C phases while lower spacer shows nematic and smectic A phases.
Highlights
E identi cation of the mesophases and determination of phase transition temperatures were achieved with the help of polarizing optical microscope (POM). e sample placed between a clean untreated glass slide and a cover slip was used for this particular study. e mesophase assignment was based on the observation of birefringence and uidity when examined under Polarizing Optical Microscope (POM)
To con rm the transition temperatures and to determine their associated enthalpies, a differential scanning calorimeter (DSC) calibrated using pure indium was employed. e peaks observed in Differential Scanning Calorimeter (DSC) traces due to phase transition were reproducible and peak temperatures were consistent with those deduced from the optical experiments
We have synthesized liquid crystalline dimers possessing two nonsymmetrical entities connected by exible spacers. Molecular design of this dimer incorporates the biphenyl and azo benzene segments interconnected through methylene spacers
Summary
E liquid crystalline state is characterized by the orientational ordering of its constituent molecules, and transitions between different mesophases are accompanied by changes in the local molecular order. ese transitions are usually marked by changes in various anisotropic properties, but depending on the order of the transition they may be accompanied by changes in scalar quantities such as enthalpy content or density. e alternations in density and thermal expansivity which accompany the nematic to isotropic phase transition have been the subjects of a number of investigations [1,2,3,4,5,6,7]. e architecture and functionalization are the essential aspects in the molecular engineering of liquid crystal for the control of important physical properties such as optical anisotropy, dielectric anisotropy, supramolecular order, and thermal stability of mesophases. e initial interest in liquid crystal dimers arose, from their potential use as model compounds with which to understand the more complex polymeric systems. E liquid crystal dimer consists of mesogenic units separated by exible spacers, normally alkyl chains [9]. Is includes the dramatic dependence of their transitional properties on the length and parity of the exible spacers linking the mesogenic units [12], the observation of a nematic-nematic transition [13], and the occurrence of alternating smectic phases [14].
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