Motion, creation and annihilation of disclinations in multi-domain structured nematic liquid crystal cells

Abstract

We study dynamical processes in a multi-domain (MD) structured nematic liquid crystal cell with a particular emphasis on the motion, creation and annihilation of disclinations. In the MD cell right- and left-handed director helices alternate due to a special choice of the director pretilt angles at the surfaces. As a result, a net of twist disclinations occurs. We have implemented a numerical algorithm based on a pure rotational dynamics of the director field to monitor the motion of the defect lines during the switching process, i.e., when an electric voltage is applied to or removed from the cell. We demonstrate that the total light transmission versus time is not affected by the presence of the defects compared to a conventional twisted nematic (TN) cell. If the pretilt angles at the surfaces are sufficiently small, the twisting sense of one species of helices is reversed and a configuration free of defects occurs. On the other hand, for an applied voltage twist disclinations close to the surface have to exist. Therefore, defect lines are created or they annihilate during the switching process. We investigate these situations in detail and reveal the underlying mechanisms.