Kinetics of Field Alignment and Elastic Relaxation in Twisted Nematic Liquid Crystals
It has been shown by Schadt and Helfrich1 that the orientation pattern of nematic liquid crystals can be made to correspond to the planar texture of cholesteric liquid crystals if the molecular alignment is parallel to the walls but differs in direction at the two surfaces. Such an arrangement is known as a twisted nematic. A 90° twist leads to a 90° rotation of linearly polarized light travelling normally to the orienting surfaces provided the direction of polarization is collinear with the aligned nematic molecules at either of the two surfaces. These authors have further shown that the application of a sufficiently high electric field between the surfaces destroys the molecular twist in the liquid crystal bulk and eliminates most of the rotation of the polarized light provided the material has a positive dielectric anisotropy1. Upon removal of the field, the initial orientation pattern is re-established.
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