Dynamics of the periodic distortions in confined nematic liquid crystals imposed by a strong orthogonal electric field

• We have studied the nematic director relaxes under strong electric field.
• Pattern evolution due to the turn-on and turn-off fields has been found.
• Velocity fields correlated to the patterns in nematic have been obtained.

The dynamics of the periodic distortions in confined nematic liquid crystals (LCs) has been investigated theoretically based on the hydrodynamic theory including the director motion with appropriate boundary and initial conditions. Analysis of the numerical results for the turn-on process provides evidence for the appearance of the spatially periodic patterns in confined LC film, only in response to the suddenly applied strong electric field. It has been shown that there is a threshold value of the amplitude of the thermal fluctuations of the director over the LC sample which provides the non uniform rotation mode rather than the uniform one, whereas the lower values of the amplitude dominate the uniform mode. During the turn-off process, the reorientation of the director to the direction preferred by the surfaces is characterized by the complex destruction of the initially periodic structure to a monodomain state. Analysis of evolution of the director distribution in the LC film under the influence of the pretransitional fluctuations when the temperature goes to the bulk nematic-smectic A transition temperature TNATNA shows that there is two scenarios of the evolution. First, in the reduced temperature range -5⩽logTTNA-1⩽-2, dominate the non uniform rotation mode and the growing pretransitional fluctuations does not destructed the initially periodic structure, whereas at the lower temperature towards TNATNA, the reorientation of the director field is characterized by the complex destruction of the initially periodic structure to a monodomain state with the director field aligned parallel to the direction preferred by the surfaces.