Electrostatically controlled surface boundary conditions in hybrid molecular-colloidal liquid crystals

In fundamental studies of liquid crystal (LC) colloids, surface interactions define the boundary conditions for molecules on particle surfaces and ultimately determine the induced defects and interactions. We study the influence of surface charge and ions on surface anchoring properties, with a focus on defining the behavior of anisotropic colloids dispersed in a nematic LC. We demonstrate a systematic variation of boundary conditions through controlling the competing aligning effects of surface functionalization and electric field arising from surface charging and bulk counterions. The control of ionic content in the bulk and at surfaces allows for tuning the equilibrium orientations of charged colloidal particles with respect to the far-field director n. When dispersed in high concentration, the charged colloids form biaxial nematic, columnar, and crystalline assemblies with tunable symmetries and ordering enabled by the anisotropic elastic and electrostatic interactions.