Surface driven pattern formation is an intriguing phenomenon in the liquid crystal field. Owing to its ability to transmit torque, one can generate different patterns by propagating distortions on the optical wavelength scale in the sample from the surface. Here, we theoretically investigate (from the elasticity point of view) twist deformations induced by a rotating easy axis at one surface, by considering the anchoring energy and surface viscosity of nematic and chiral nematic samples. The model is solved analytically in the limit of strong anchoring and numerically for a low anchoring strength situation. Such rotation could be induced, in principle, by light-controlling the orientation of an azobenzene monolayer coated at one of the glass substrates or by an in-plane rotating field. We discuss the role of the surface parameters and the different distortions, and calculate light transmission using the Jones method. Three different regimes are identified: free twist, stick-slip twist, and constrained twist. The results obtained here may be relevant for liquid crystal active waveplates and for determining surface viscosity and the azimuthal anchoring energy.

中文翻译：

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向列和手性向列液晶的表面诱导扭曲：粘滑状和受约束的运动†

在液晶领域中，表面驱动图案的形成是一种令人着迷的现象。由于其传递扭矩的能力，人们可以通过从表面传播样品中光波长尺度上的畸变来生成不同的图案。在这里，我们从理论上研究（从弹性的角度）通过考虑向列和手性向列样品的锚固能和表面粘度，在一个表面上由易旋转轴引起的扭曲变形。该模型在强锚固的极限情况下通过解析求解，而在锚固强度较低的情况下则通过数值求解。原则上，可以通过光控制涂覆在玻璃基板之一上的偶氮苯单层的取向或通过面内旋转场来引起这种旋转。我们讨论了表面参数和不同变形的作用，并使用琼斯方法计算透光率。确定了三种不同的状态：自由扭曲，粘滑扭曲和约束扭曲。此处获得的结果可能与液晶有源波片有关，也与确定表面粘度和方位锚固能量有关。