Magnetic Field Driven Configuration Transitions in Nematic Droplets

We experimentally study the director configuration evolution in a nematic liquid crystal (NLC) droplet in a uniform magnetic field. To date, the magnetic field driven transition from a radial configuration to an axial configuration has been predicted in theory and simulation, but has yet to be critically examined experimentally. To this end, we built an apparatus to observe NLC droplets in high-magnetic fields using polarized optical microscopy. Our observations reveal that the transformation from radial to axial configuration has two intermediary states: a "deformed radial" state and an "axial with defect" state. We examine these transition states through experiment and numerical simulation and discuss their characteristics in the context of current literature. Building on prior work, we develop a critical field model to describe the relationship between critical magnetic field and droplet radius for a droplet with finite anchoring strength. Finally, by identifying critical fields for a range of droplet sizes and surfactant concentrations, we use the model to estimate anchoring strength at a liquid-liquid interface for commonly used surfactants and concentrations.