Programming Liquid Crystal Director Fields Using Spatially Varying Magnetic Fields

Magnetic fields can be used to control the director orientation in liquid crystals. The resulting anisotropic texture is implicitly associated with anisotropy of material properties, including dielectric permittivity and elasticity. Here we show that the director field of a small molecule LC can be spatially programmed by employing magnetic microstructures. Microstructured ferromagnetic materials, such as cobalt, distort the uniformity of a background field and cause spatial variation of field strength and direction. Mesogens confined between surfaces with homeotropic anchoring undergo a Freedericksz transition to a planar configuration above a critical field strength set by the sample thickness and anchoring energy. In this configuration, the local variation in field strength due to the Co magnetic microstructures results in a readily observable spatial variation of the LC director field that is encoded or programmed by the magnetic field. We explore various geometrical arrangements of cobalt microstructures and the director field configurations that result from the magnetic field patterns formed by these arrays. We reconcile the results using simulations of the spatial variation of the magnetic field and LC director field. This approach enables the generation of bespoke director field patterns, with inverse design methodologies connecting required magnetic array geometries to desired director field patterns. The embedded local control of material properties provides a feasible route to spatially programming material function.