Department of

Chemical Engineering

Designing molecular technology for the 21st century with biology and chemistry


Fall 2011 Seminars

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Colloidal Interactions, Dynamics, and Assembly on Energy Landscapes



Michael A. Bevan
Associate Professor, Department of Chemical & Biomolecular Engineering
Johns Hopkins University

Thursday, October 6
10:00 a.m. - 11:00 a.m.
102 Chemistry Building

Abstract
The ability of nano- and micro- scale components to autonomously and reversibly assemble into ordered configurations is often suggested as a basis for scalable manufacturing processes capable of producing meta-materials with exotic electromagnetic properties (e.g. photonic band gap, negative refraction) that could enable numerous 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 the development of the science and applications of such materials. As a result, there is strong interest in understanding how thermal motion, particle interactions, patterned surfaces, and external fields can be optimally coupled to robustly control the assembly of nano- and micro- scale components into ordered configurations.

We approach this problem by directly relating equilibrium and dynamic colloidal microstructures to kT-scale energy landscapes mediated by colloidal forces, physically and chemically patterned surfaces, and gravitational and electric fields. 3D colloidal trajectories are measured in real-space and real-time with nanometer resolution using a suite of integrated evanescent wave, video, and confocal microscopy methods. In analyses of trajectories, 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 depletion and electric field mediated interactions is modeled using a novel approach.

Specifically, the Smoluchowski equation is "fit" to experimental microscopy and computer simulated assembly trajectories using order parameters that capture important microstructural features of crystallization processes. This approach rigorously captures both statistical mechanical (free energy changes) and fluid mechanical (hydrodynamic interactions) contributions associated with changing microscopic configurations. With the ability to measure and tune kT-scale colloidal interactions and quantitatively model how such interactions are connected to dynamically changing microstructures, we demonstrate the real-time control of the assembly, disassembly, and repair of colloidal crystals using both open loop (recipe based) and closed loop (feedback) control to produce perfect single colloidal crystals.

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