Magnetic Effects in Confined Nematic Liquid Crystal Droplets

We study the structural transition of nematic liquid crystal (NLC) droplets with homeotropic anchoring in a uniform magnetic field. Confining NLC in droplets creates competition between surface anchoring energy and bulk elasticity, giving rise to distortions and defects. The effects of an electric field on the equilibrium director conformation of NLC droplets are well known, but studies using a magnetic field are scarcer due to the low magnetic susceptibility of most NLCs. We have developed a variable magnet mounted on a polarized microscope that can deliver up to 0.5T of uniform field. With this mechanism, we study the stability of hedgehog defects and the resulting Fréedericksz transition in NLC droplets. We confirm, as predicted theoretically, the formation of a ring defect whose radius increases with field strength as the director approaches a uniformly aligned state. We establish stability diagrams for NLC droplets of various radii and conduct comparative analysis of experimental and calculated threshold fields. Overall, this project aims to elucidate the director configurations of NLCs in confined geometries and to explore their bulk response to external magnetic fields.