Distortions in structures of the twist bend nematic phase of a bent-core liquid crystal by the electric field

K. Merkel, A. Kocot, J. K. Vij, and G. Shanker
Phys. Rev. E 98, 022704 – Published 31 August 2018

Abstract

The dielectric spectra of the twist bend nematic phase (NTB) of an achiral asymmetric bent-core liquid crystalline compound are studied for determining the various relaxation modes. Dielectric measurements are also carried out under the bias field E up to 8 V/µm. Two molecular and two collective relaxation processes are observed. The orientational order parameters with respect to the local and the main directors determined using molecular modes are used to find the heliconical angle. The results also show that the order parameter with reference to the main director reverses its trend from increasing to decreasing at temperatures of a few degrees above the NTB to N transition. The collective relaxation modes are assigned to (a) distortions of the local director by the electric field at a frequency of 100kHz while the periodic helical structure remains unaltered (mode attributed to flexoelectricity); (b) changes in the periodic structure arising from a coupling of the dielectric anisotropy with the electric field at the lowest frequency in the range of 100 Hz–10 kHz. Frequency of the higher frequency collective mode (100kHz) depends primarily on the heliconical angle and has anomalous softeninglike behavior at the NNTB transition. The lowest frequency mode is studied under the bias field E; the modulus of the wave vector gradually vanishes on increasing E (except for an initial behavior, E2<0.1V2/μm2, which is just the opposite). The transition from the twist bend to splay bend structure is observed by a sudden drop in the frequency of this mode, followed by a linear decrease in frequency by increasing E. The results agree with the predictions made from the currently proposed models for a periodically distorted NTB phase.

  • Figure
  • Figure
  • Figure
  • Figure
  • Figure
  • Figure
  • Figure
  • Received 6 March 2018

DOI:https://doi.org/10.1103/PhysRevE.98.022704

©2018 American Physical Society

Physics Subject Headings (PhySH)

  1. Physical Systems
Polymers & Soft Matter

Authors & Affiliations

K. Merkel1,*, A. Kocot1, J. K. Vij2,†, and G. Shanker3

  • 1Institute of Material Science, Silesian University, Katowice 40-007, Poland
  • 2Department of Electronic and Electrical Engineering, School of Engineering, Trinity College Dublin, The University of Dublin, Dublin 2, Ireland
  • 3Department of Studies in Chemistry, Jnana Bharathi Campus, Sneha Bhavan, Bangalore University, Bangalore 560056, India

  • *merkelkatarzyna@gmail.com
  • jvij@tcd.ie

Article Text (Subscription Required)

Click to Expand

References (Subscription Required)

Click to Expand
Issue

Vol. 98, Iss. 2 — August 2018

Reuse & Permissions
Access Options
CHORUS

Article Available via CHORUS

Download Accepted Manuscript
Author publication services for translation and copyediting assistance advertisement

Authorization Required


×
×

Images

×

Sign up to receive regular email alerts from Physical Review E

Log In

Cancel
×

Search


Article Lookup

Paste a citation or DOI

Enter a citation
×