Orientational Instability Induced by the Electric Field in a Cell of a Nematic Liquid Crystal with Negative Dielectric Anisotropy
Keywords:nematic liquid crystal, negative dielectric anisotropy, orientational instability, easy axis gliding, switching-on/off time, Fr´eedericksz transition
The orientational instability of the director induced by an external dc electric field in the homeotropic cell including a nematic liquid crystal with negative dielectric anisotropy has been studied. The easy axis gliding in the plane perpendicular to either of polymer cell substrates is taken into consideration. It is explained by the reorientation of the elastic fragments of polymer molecules of the cell substrate owing to the interaction between the permanent or induced dipole moments of the substrate molecules and the electric field. In both cases, the orientational instability of the liquid crystal director is found to have a threshold character. The evolution of the nematic director and the easy axis is analyzed since the moment of electric field switching-on, during the system transition into a stationary state, and until the system relaxes into the initial homogeneous state after the electric field is switched-off. The calculated time dependences of the easy-axis deviation angle are compared with the literature experimental data.
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