Department of Materials Science Spring Seminar Series: Michael Bevan

Description

Michael A. Bevan, a professor of chemical and biomolecular engineering at Johns Hopkins , will give a talk titled "Controlling Self Assembly in Colloidal Materials" for the Department of Materials Science.

Assembly of colloidal nano- and micro-particles into ordered configurations is often suggested as a scalable process to manufacture microstructured materials with exotic multifunctional properties (e.g., mechanical, optical, electrical, porosity, etc.). Such processes could yield high-value-added materials to enable emerging technologies and advancements to particle based coatings, membranes, composites, and reconfigurable 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, repair, and reconfiguration of colloidal microstructures using open loop and closed loop control to produce perfectly ordered states. 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 devices.