Surface Limitations to the Electro-Mechanical Tuning Range of Negative Dielectric Anisotropy Cholesteric Liquid Crystals

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Journal of Applied Physics

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Recent work on negative dielectric anisotropy cholesteric liquid crystals (CLCs) showed that externally applied dc voltages resulted in blue tuning of the reflection band position up to 20% of its original position. These results also showed that the observed shift in reflection band position was not caused by a direct interaction between the CLC and the applied voltage, but indirectly through electromechanical stresses that deformed the conductive glass substrates, in turn deforming the liquid crystal. In this work, the goal is to clarify that the major limiting factors on the tuning range limit result from the magnitude of the surface anchoring energy and surface induced hysteresis effects. An analytic solution for the tuning range limit and its dependence on the surface and bulk properties is derived that agrees well with the experimental data. Using this model, it was shown that tuning range limits in excess of 35% of the notch position should be expected with typically available alignment materials, and that with proper CLC/surface optimizations, values in the range of 75% are possible.


Copyright 2012 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in J. Appl. Phys. 111, 063111 (2012) and may be found at http://dx.doi.org/10.1063/1.3694023.