Nanosecond electro-optics of a nematic liquid crystal with negative dielectric anisotropy

Volodymyr Borshch, Sergij V. Shiyanovskii, Bing-Xiang Li, and Oleg D. Lavrentovich
Phys. Rev. E 90, 062504 – Published 9 December 2014

Abstract

We study a nanosecond electro-optic response of a nematic liquid crystal in a geometry where an applied electric field E modifies the tensor order parameter but does not change the orientation of the optic axis (director N̂). We use a nematic with negative dielectric anisotropy with the electric field applied perpendicularly to N̂. The field changes the dielectric tensor at optical frequencies (optic tensor) due to the following mechanisms: (a) nanosecond creation of the biaxial orientational order, (b) uniaxial modification of the orientational order that occurs over time scales of tens of nanoseconds, and (c) the quenching of director fluctuations with a wide range of characteristic times up to milliseconds. We develop a model to describe the dynamics of all three mechanisms. We design the experimental conditions to selectively suppress the contributions from the quenching of director fluctuations (c) and from the biaxial order effect (a) and thus, separate the contributions of the three mechanisms in the electro-optic response. As a result, the experimental data can be well fitted with the model parameters. The analysis provides a rather detailed physical picture of how the liquid crystal responds to a strong electric field on a time scale of nanoseconds. The paper provides a useful guidance in the current search for the biaxial nematic phase. Namely, the temperature dependence of the biaxial susceptibility allows one to estimate the temperature of the potential uniaxial-to-biaxial phase transition. An analysis of the quenching of director fluctuations indicates that on a time scale of nanoseconds, the classic model with constant viscoelastic material parameters might reach its limit of validity. The effect of nanosecond electric modification of the order parameter can be used in applications in which one needs to achieve ultrafast (nanosecond) changes in optical characteristics, such as birefringence.

    • Received 27 August 2014

    DOI:https://doi.org/10.1103/PhysRevE.90.062504

    ©2014 American Physical Society

    Authors & Affiliations

    Volodymyr Borshch1,*, Sergij V. Shiyanovskii1, Bing-Xiang Li1,2, and Oleg D. Lavrentovich1,†

    • 1Liquid Crystal Institute, Chemical Physics Interdisciplinary Program, Kent State University, Kent, Ohio 44242, USA
    • 2College of Electronic and Information Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China

    • *Current address: Apple, Inc., Cupertino, CA 95014, USA.
    • olavrent@kent.edu

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    Issue

    Vol. 90, Iss. 6 — December 2014

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