CBE Seminar Series: Mike Bevan, Johns Hopkins University




Colloidal Interactions, Dynamics & Assembly on Energy Landscapes Michael A. Bevan, Chemical & Biomolecular Engineering, Johns Hopkins University Abstract: Assembly of colloidal nano- and micro- particles into ordered configurations is often suggested as a scalable process to manufacture microstructured materials with exotic properties. Such processes could yield high value added materials to enable emerging technologies and advancements to particle based coatings, complex fluids, and composite materials. Although natural materials display diverse ordered microstructures formed via geological or morphogenetic processes, it has been challenging to produce synthetic materials in engineered processes with similar order and low defect densities. To solve this engineering challenge, it is essential to understand how Brownian motion, colloidal interactions, and collective dynamics can be controlled to assemble colloidal scale components into hierarchically structured functional materials. In this talk, I will discuss my group’s approach to this problem by implementing feedback control over colloidal assembly processes. Our approach is enabled by directly relating dynamic colloidal microstructures to kT-scale energy landscapes mediated by interactions between colloids, surfaces, and external fields. 3D colloidal trajectories are measured in real-space and real-time with nanometer resolution using an integrated suite of evanescent wave, video, and confocal microscopy methods. Equilibrium structures are connected to energy landscapes via statistical mechanical models. The dynamic evolution of initially disordered colloidal fluid configurations into ordered colloidal structures via tunable interactions is modeled by fitting the Smoluchowski equation to experimental microscopy and computer simulated assembly trajectories. This approach employs reaction coordinates that capture important microstructural features of non-equilibrium assembly processes and rigorously quantify both statistical mechanical (free energy) and fluid mechanical (hydrodynamic) contributions. With the ability to measure and tune kT-scale colloidal interactions and quantify how such interactions are connected to dynamically changing microstructures, we demonstrate real-time control of assembly, disassembly, and repair of colloidal crystals using both open loop and closed loop control to produce perfectly ordered microstructures. This approach is demonstrated for close packed colloidal crystals of spherical particles along with extensions to anisotropic particles and patterned hierarchical microstructures. Ultimately, our approach demonstrates formal control over non-equilibrium dynamic processes in colloidal systems, which can be extended to diverse materials and control objectives involving non-equilibrium targets, particle navigation, and colloidal machines. Biography: Michael A. Bevan is a Professor of Chemical & Biomolecular Engineering at Johns Hopkins University. He received his Ph.D. from Carnegie Mellon University in 1999. After post-doctoral appointments at the University of Melbourne, Australia, and the University of Illinois at Urbana-Champaign, he joined Texas A&M University in 2002 and Johns Hopkins University in 2008. Bevan's research investigates interactions, dynamics, and structure in interfacial colloidal systems. Bevan is a recipient of a CAREER award and a PECASE from the National Science Foundation, and he was elected as a Fellow of the American Chemical Society in 2016.