Spatially periodic deformations in planar and twisted flexoelectric nematic layers.

Electric field induced deformations in twisted and untwisted planar layers of nematic liquid crystals possessing flexoelectric properties were investigated numerically. The spatially periodic deformations, taking the form of parallel stripes, were found to have smaller free energy than the homogeneous deformations. The structures of distorted layers as well as the evolution of deformations during changes of bias voltage were recognized. The role of flexoelectric properties was analyzed. Calculations taking into account the peculiar elastic properties of the bent-core nematics were also performed. In the untwisted planar layers the stripes were parallel to the initial director orientation. In the twisted layers, two different kinds of periodic deformation were distinguished. They had different structures and different directions with respect to the initial director distribution. The results were consistent with existing experimental data.