Dielectric properties of liquid crystalline dimer mixtures exhibiting the nematic and twist-bend nematic phases

Nina Trbojevic, Daniel J. Read, and Mamatha Nagaraj
Phys. Rev. E 96, 052703 – Published 14 November 2017
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Abstract

A detailed investigation of the thermal and dielectric properties of a series of binary mixtures exhibiting the nematic (N) and twist-bend nematic (NTB) liquid crystal phases is presented. The mixtures consist of an achiral, dimeric liquid crystal CB7CB, which forms the nematic and twist-bend nematic phases, and a calamitic liquid crystal 5CB, which shows the nematic phase. As the concentration of the calamitic liquid crystal is increased, the transition temperatures decrease linearly, and the width of the nematic phase increases. The enthalpies of phase transitions obtained from DSC measurements show that on increasing the concentration of 5CB in the binary mixtures, the enthalpy associated with the NNTB phase transitions reduces considerably compared to a clear first-order NNTB transition in pure CB7CB. The real and imaginary parts of the dielectric permittivity are measured as a function of frequency from 100 Hz to 2 MHz in the nematic and twist-bend nematic phases in planar and homeotropic devices. A significant decrease in the average dielectric permittivity as a function of temperature for mixtures forming the NTB phase is observed. Measurements of the imaginary part of the dielectric permittivity show a relaxation peak in the measured frequency window for all of the mixtures exhibiting the NTB phase. The activation energy associated with this relaxation process is calculated and is shown to remain constant irrespective of the composition of the mixtures.

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  • Received 5 June 2017

DOI:https://doi.org/10.1103/PhysRevE.96.052703

©2017 American Physical Society

Physics Subject Headings (PhySH)

Polymers & Soft Matter

Authors & Affiliations

Nina Trbojevic1, Daniel J. Read2, and Mamatha Nagaraj1,*

  • 1School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, United Kingdom
  • 2School of Mathematics, University of Leeds, Leeds LS2 9JT, United Kingdom

  • *Corresponding author: m.nagaraj@leeds.ac.uk

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Issue

Vol. 96, Iss. 5 — November 2017

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