Director configurations of nematic-liquid-crystal droplets: Negative dielectric anisotropy and parallel surface anchoring

Abstract

We have identified the director configurations n(r) of nematic droplets subjected to electric fields under conditions of negative dielectric anistropy and parallel surface anchoring. Drops are examined using polarization microscopy, with electric fields applied parallel or perpendicular to the light direction. The behavior of the resulting textures and defects is obtained by comparing the droplet appearance with computer simulated transmission patterns using intuitively obtained model director configurations. In the field-off state, the director is essentially azimuthal (concentric texture) near the surface, ‘‘escaping’’ to the axis direction (bipolar texture) along the droplet axis. For low fields, the director configuration becomes either more bipolar or more concentric depending on whether the droplet axis is initially parallel or perpendicular to the electric field. For high fields, the bipolar structure evolves into one in which the directors form planar bipolar sheets escaped at the poles (escaped planar bipolar texture). The concentric structure, however, becomes unstable and a novel transition to the more stable escaped planar bipolar structure is described.