Controlled Colloidal Assembly Via Navigation of Energy Landscapes
Daniel J. Beltrán–Villegas and Michael A. Bevan. Chemical and Biomolecular Engineering, Johns Hopkins University, 221 Maryland Hall, 3400 North Charles Street, Baltimore, MD 21218
This talk will present simulation results for the feedback controlled assembly of interfacial colloidal crystals with pyramidal morphologies. In particular, Monte Carlo and Stokesian Dynamic simulations are used to monitor assembly of colloidal crystals on patterned surfaces as attractive depletion potentials are tuned in a controlled fashion. Assembly processes are characterized as trajectories on energy landscapes (EL)s analogous to models of protein folding. Specifically, assembly trajectories are quantified by temporal changes in positions on ELs defined by order parameters (e.g. radius of gyration, bond orientational order, short-time self-diffusion coefficients) that capture various features of the interfacial crystallization process (e.g. condensation, geometric ordering, local transport, etc.). Initial work has identified order parameters that accurately capture important features of assembly processes including undesirable states (e.g. arrested configurations), desirable transition states, and proper formation of the final structure. Assembly is controlled by comparing “process values” for experimental trajectories with “set values” from ideal trajectories that successfully navigate troublesome features on ELs towards the free energy minimum structure of interest. Actuation to correct differences in process and set trajectories via feedback control is achieved by tuning depletion attraction that can partly disassemble and reinitiate assembly processes as needed. Results will be shown for dynamic system response, controller effectiveness, limitations, and ongoing work related to efficient EL construction.