(77a) Controlling Colloidal Interactions, Dynamics, and Assembly

Bevan, M. A. - Presenter, Johns Hopkins University

The ability of nano- and micro- scale components to autonomously and reversibly assemble into ordered configurations on surfaces is often suggested as a scalable manufacturing process capable of producing materials with exotic properties (e.g. photonic band gap, negative refraction) that could enable emerging technologies (e.g. optical computing, sub-diffraction limit imaging, invisibility cloaking). However, the inability to produce such ordered materials in a robust manner and with a sufficiently low defect density has limited their development of applications. As a result, there is strong interest in understanding how thermal motion, particle interactions, patterned surfaces, gravity, and other external fields can be optimally coupled to robustly control the assembly of colloidal components into ordered configurations.

We approach this problem by directly relating equilibrium and dynamic colloidal microstructures to kT-scale interactions. 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 colloidal crystals in the presence of tunable interactions (polymer depletion, electric fields) is modeled by fitting the Smoluchowski equation to experimental microscopy and computer simulated assembly trajectories. This approach is based on the use of reaction coordinates that capture important microstructural features of crystallization 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 quantitatively model how such interactions are connected to microstructural dynamics, we demonstrate the real-time open loop and closed loop control of the assembly, disassembly, and repair of colloidal crystals.