Closed Loop Navigation of a Complex State Space: Assembling Anisotropic Colloids into Perfect Crystals

Controlling the reliable rapid assembly of different shaped colloidal building blocks into low-defect microstructures is an open challenge that could enable numerous advanced material technologies. Limitations to addressing this problem include scientific challenges with understanding nonequilibrium microstructure evolution and technological challenges with controlling such stochastic dynamic processes. To navigate a complex multistate colloidal assembly process, here we implement closed loop-controlled assembly of rectangular particle monolayers in AC electric fields, which can form over a dozen states including multiple liquid, liquid crystal, crystal, and glassy states. In optical microscopy experiments, we navigate between multiple stable, metastable, and transient states with varying degrees of particle orientational and positional order by implementing kT-scale tunable dipolar potentials, identifying low dimensional reaction coordinates that capture all states and pathways, and designing control policies informed by microstructure evolution on underlying free energy landscapes. The resulting control scheme enables rapid assembly along dynamic pathways on different energy landscapes that circumvent and/or repair orientational defects in nematic states and positional defects in crystal states. Our findings demonstrate a generalizable first-principles approach to control microscopic assembly processes with broad implications to understanding stochastic nonequilibrium self-assembly dynamics and realizing high-value-added microstructured materials.