ChBE Seminar Series: James F. Gilchrist
Tuesday, September 15, 2009
11:00 a.m.-12:15 p.m.
Room 2110, Chemical and Nuclear Engineering Bldg.
Professor Richard Calabrese
Particle Migration and Self-Organization in Simple and Chaotic Flows
Presented by James F. Gilchrist
Department of Chemical Engineering
Center for Advanced Materials and Nanotechnology
Self-organization arises in systems when constituents having local repulsion are confined or have a long range attraction, resulting in rich phase behavior and/or pattern formation. However, it is generally unclear how these systems behave when subjected to deformation or when self-organization is coupled to the underlying flow. Two prototypical systems will be discussed, both of which have practical application in device fabrication and suspension handling.
Convective deposition of nano- and microscale particles is used to fabricate surface morphologies such as microlens arrays atop light emitting diodes (LEDs) to enhance the photon extraction efficiency by over 300% and various other energy, optical, and BioMEMS applications. The fundamental mechanism behind self-organization of these particles is the local capillary interactions of particles confined in a thin film of an advancing meniscus. Previous investigations of this ?coffee ring effect? neglect many critical parameters involved with the deposition process that are highlighted in this study. We will highlight resulting morphology and various instabilities that occur during deposition of uni- and bimodal suspensions.
We also investigate the competition between chaos-enhanced dispersion and self-organization of particle suspensions in microfluidic channels. In steady pressure-driven flows, self-organization occurs due to multibody hydrodynamic interactions, typically driving particles away from the walls toward the center of the channel despite the diffusive motion of the particles. In channels whose geometry induces flow in the transverse direction to the pressure gradient, direct competition between particle self-organization and mixing due to advection results in concentration profiles where the underlying 3D flow acts as a template for pattern formation. The internal structure of these suspensions is investigated in an attempt to elucidate the details of the interactions that result in self-organization. We demonstrate this interplay is critical in designing microscale devices that handle suspensions such as blood for BioMEMS, and suggest a new paradigm in enhanced mixing and separations.