Feedback Controlled Reconfiguration of Ellipsoidal Colloids between Interfacial Liquid, Nematic, and Crystal States

We report AC electric field mediated feedback control over the reversible assembly, disassembly, and reconfiguration of elliptical prism colloidal particles between liquid, nematic, and crystal states with continuously varying orientational and positional order. Accessible states are first systematically identified by varying field parameters and quantifying microstructures with nematic and crystallinity order parameters. The same order parameters vs time are used as reaction coordinates to track nonequilibrium microstructure evolution between states. A proportional feedback controller for reaction coordinate trajectories is designed to target microstructures with different degrees of order, where gain constants are tuned to maximize transition rates between states orders of magnitude faster than diffusion limited rates (on second to minute time scales). The resulting feedback control approach is demonstrated for time-dependent reaction coordinate trajectories including sinusoidal, step changes, and programmed multistate profiles. Our results and findings demonstrate a generalizable scalable approach to formally control navigation of dynamic pathways between microstructural states in a system of anisotropic colloidal particles, which can be used to control processing of particle-based materials, coatings, and devices.