Optical rotation at the free surface of a nematic liquid crystal

When a small droplet of a nematic liquid crystal is placed on a horizontal glass plate in the presence of a magnetic field, the plane of polarization of light transmitted upward through the liquid crystal can be rotated. A defect usually forms preferring a direction perpendicular to the magnetic field and forming a diagonal of the droplet. This defect divides the free surface into regions giving rise to optical rotations that are clockwise and counterclockwise. It is suggested that the defect may be similar to a Helfrich splay-bend wall and the optical rotation in the regions near the defect may be explained by surface effects at the free surface of a liquid crystal.