Switching of negative and positive dielectro-anisotropic liquid crystals by in-plane electric fields

This article compares switching behaviors between negative $(Nn)$ and positive $(Np)$ dielectro-anisotropic nematic liquid crystals driven by an in-plane electric field which is generated with interdigital electrodes. Even for $Np$ type liquid crystals, excellent viewing angle characteristics were obtained as expected. Theoretical descriptions of the switching principle, i.e., threshold behavior and response mechanism, could be applied to both the $Nn$ and $Np$ type liquid crystals. However, the orientational deformation of the $Np$ type liquid crystals caused by a distorted electric field which occurred near the edges of electrodes was not the same as that of the $Nn$ type liquid crystals. The switching of the $Np$ type liquid crystals near the edges of the electrodes by this field was followed by the in-plane switching of the liquid crystals between the electrodes. This remarkably distinctive dynamical behavior implied a difference in the response of the longitudinal axes for $Nn$ and $Np$ type liquid crystal molecules. The longitudinal axes of the latter seemed to be sensitive to the electric field component perpendicular to the substrates when applying the in-plane electric field. Furthermore, these experimentally obtained results were supported by computer simulations which analyzed the liquid crystal director distribution and transmittance pattern from edge-to-edge of a pair of electrodes when applying the in-plane electric field.