Modeling Reorientation Dynamics of Electrically Assisted Light-Induced Gliding of Nematic Liquid-Crystal Easy Axis

Abstract

The phenomenological torque balance model previously introduced to describe the electrically assisted light-induced gliding is generalized to study the reorientation dynamics of the nematic liquid crystal easy axis at photoaligned azo-dye films under the combined action of in-plane electric field and reorienting UV light linearly polarized at varying polarization azimuth,φp. We systematically examine the general properties of the torque balance model by performing analysising the bifurcations of equilibria at different values of the polarization azimuth and apply for the model to interpret the experimental results. These involve observation of the pronounced purely photoinduced reorientation atφp≠0, as opposed to the case where the light polarization vector is parallel to the initial easy axis (φp=0), and the reorientation is almost entirely suppressed. In the regions between electrodes with nonzero electric field, the effects described by the model are that (a) the dynamics of reorientation slows down withφpand (b) the sense of easy axis rotation is independent of the sign ofφp.

Orientational Instability Induced by the Electric Field in a Cell of a Nematic Liquid Crystal with Negative Dielectric Anisotropy

“…Then the process of relaxation can be described in the approximation of small and angles, by using the linearized Eq. (9) with the boundary conditions (10)- (12), in which = 0. The required, finite at → +∞, solution for the deviation angles of the director and the moving easy axis looks like .…”

“…The authors of works [10][11][12] proposed a phenomenological model for the easy axis reorientation at the surface of a polymer substrate under the influence of an electric field, but in the azimuthal direction. The model is based on the phenomenon of NLC molecule adsorption.…”

Director gliding in a nematic liquid crystal layer: Quantitative comparison with experiments

“…Experiments have shown that if a strong applied torque exists for extended periods of time, the easy axis can slowly rotate, leading to a phenomenon known as easy axis gliding or director gliding [1] (the director is a unit vector characterizing the average molecular orientation of the long axis of the molecules). Director gliding has been observed in lyotropic, thermotropic and nematic LCs with multiple experiments reporting both zenithal and azimuthal gliding [1][2][3][4][5][6][7][8].…”

Instability of Director Orientation in a Planar Nematic Cell under Tunable Boundary Conditions in the Electric Field

“…The processes of NLC director and easy axis reorientations in the polymer substrate plane in a strong ac electric field and the relaxation of a system after the field switching-off were studied experimentally and theoretically in work [8]. The simultaneous action of the ac electric field and polarized light on the NLC director dynamics near the polymer surface preliminarily illuminated with ultraviolet was studied in works [9,10]. In works [8][9][10], the easy axis reorientation was explained in the framework of a scenario that is based on the adsorption of NLC molecules on the substrate surface.…”

“…The simultaneous action of the ac electric field and polarized light on the NLC director dynamics near the polymer surface preliminarily illuminated with ultraviolet was studied in works [9,10]. In works [8][9][10], the easy axis reorientation was explained in the framework of a scenario that is based on the adsorption of NLC molecules on the substrate surface. The phenomenological model of the phenomenon, which was proposed in those works, involves the influence of the nematic volume on the easy axis motion, decelerating action of polymer, and viscosity of the easy axis motion.…”