7 October 2014 Electrooptics of chiral nematics formed by molecular dimers
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Electrically induced reorientation of liquid crystal (LC) director caused by dielectric anisotropy is a fundamental phenomenon widely used in modern technologies. We demonstrate an electrooptic effect in a chiral nematic LC with a distinct oblique-helicoidal director deformation. The effect, predicted theoretically in late 1960-ies, is observed in a chiral nematic (cholesteric) in which the ground field-free state of the director is a right-angle helicoid. In the electric field, the director forms an oblique helicoid with the pitch and cone angle controlled by the field. The effect is observed in a dimer nematic material in which the bend elastic constant is much smaller than its twist counterpart. The heliconical structure can be used in two different geometries of a sandwich-type cell, with the axis of the oblique helicoid being either parallel or perpendicular to the bounding plates. In the first case, the structure can be used as tunable diffraction grating controlled by the in-plane electric field. In the second case, the structure represents an optical Bragg reflector in which the wavelength of reflected light is controlled in a broad spectral range (from ultraviolet to infrared and beyond, depending on the composition) by a top-down electric field; it can find applications in reflective displays, tunable color filters and lasers.
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Jie Xiang, Jie Xiang, Sergij V. Shiyanovskii, Sergij V. Shiyanovskii, Yannian Li, Yannian Li, Corrie T. Imrie, Corrie T. Imrie, Quan Li, Quan Li, Oleg D. Lavrentovich, Oleg D. Lavrentovich, "Electrooptics of chiral nematics formed by molecular dimers", Proc. SPIE 9182, Liquid Crystals XVIII, 91820P (7 October 2014); doi: 10.1117/12.2062737; https://doi.org/10.1117/12.2062737


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