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Giant flexoelectricity of bent-core nematic liquid crystals

Antal Jakli ,John Harden ,Badel Mbanga ,Nandor Eber ,Katalin Fodor-Csorba ,Samuel Sprunt ²,James Gleeson ²
Chemical Physics Interdisciplinary Program and Liquid Crystal Institute, Kent State University, Kent, Ohio 44242, USA Research Institute for Solid State Physics and Optics, P. O. Box 49, H-1525 Budapest, Hungary ²Department of Physics, Kent State University, Kent, Ohio, 44242, USA
Flexoelectricity is a linear coupling between orientational deformation and electric polarization; it is a unique property of orientationally ordered materials of which nematic liquid crystals (NLCs) are the best known example. We present a direct method for measuring the flexoelectric coefficients of liquid crystals via the electric current produced by periodic mechanical flexing of the NLC’s bounding surfaces. This method is particularly suitable for measuring the response of bent-core liquid crystals, which are expected to demonstrate a much larger flexoelectric effect than traditional, calamitic (rod-shaped) liquid crystals. Our results reveal that not only is the bend flexoelectric coefficient of bent-core NLC’s gigantic (more than three orders of magnitude larger than in calamitics) but also it is much larger than would be expected from microscopic models based on molecular geometry. Thus, bent-core nematic (BCN) materials can form the basis of a technological breakthrough for conversion between mechanical and electrical energy.

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