Understanding the unusual reorganization of the nanostructure of a dark conglomerate phase

M. Nagaraj, J. C. Jones, V. P. Panov, H. Liu, G. Portale, W. Bras, and H. F. Gleeson
Phys. Rev. E 91, 042504 – Published 14 April 2015

Abstract

The dark conglomerate (DC) phase exhibited by a bent-core liquid crystal shows remarkable properties including an electric-field tunable chiral domain structure and a large (0.045) reduction of refractive index, while maintaining an optically dark texture when observed under crossed polarizers. A detailed investigation of the system is presented, leading to a model that is fully consistent with the experimental observations. It reports the observation of two distinct regimes in the DC phase: a higher temperature regime in which the periodicity measured by small angle x-ray scattering decreases slightly (0.5%) and a lower temperature regime where it increases considerably (16%). Also, the paper discusses the unusual electric-field-induced transformations observed in both the regimes. These changes have threshold fields that are both temperature and frequency dependent, though the phenomena are observed irrespective of device thickness, geometry, and the alignment layer. The electro-optic behavior in the DC phase corresponds to a number of structural changes leading to unusual changes in physical properties including a small (1%) increase in periodicity and a doubling of the average dielectric permittivity. We propose a model of the DC phase where in the ground state the nanostructure of the phase exhibits an anticlinic antiferroelectric organization. Under an electric field, it undergoes a molecular rearrangement without any gross structural changes leading to an anticlinic ferroelectric order while keeping the overall sponge-like structure of the DC phase intact.

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  • Received 22 January 2015

DOI:https://doi.org/10.1103/PhysRevE.91.042504

©2015 American Physical Society

Authors & Affiliations

M. Nagaraj1,*, J. C. Jones1,2, V. P. Panov1, H. Liu1, G. Portale3, W. Bras3, and H. F. Gleeson1,2

  • 1School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, United Kingdom
  • 2School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, United Kingdom
  • 3DUBBLE Beamline, ESRF, Grenoble 38043, France

  • *mamatha.nagaraj@manchester.ac.uk

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Vol. 91, Iss. 4 — April 2015

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