Feedback Controlled Colloidal Self-Assembly

Colloidal self-assembly provides one promising route to fabricate spatially periodic meta-materials with novel properties important to a number of emerging technologies. However, colloidal assembly is generally initiated via irreversible step-changes and proceeds along unspecified, non-equilibrium kinetic pathways with little opportunity to manipulate defects or reconfigure microstructures. Here, a conceptually new approach that enables the use of feedback control to quantitatively and reversibly guide the dynamic evolution of colloid ensembles between disordered fluid and crystalline configurations is demonstrated. The key to this approach is the use of free energy landscape models to inform feedback control laws that close the loop between real-time sensing (via order parameters) and actuation (via tunable electrical potentials). This approach, which demonstrates controlled assembly to create ordered materials and perform active reconfiguration, is based on chemical physics that suggest it can be generalized to other microscopic processes.