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W. G. Pritchard Lab Seminar: 11:15 AM - 12:15 PM, 106 McAllister Bldg

	              **Monday October 2, 2006**
	
Competition between chaotic mixing and self-organization from 
granular tumblers to microchannels

James F. Gilchrist

Department of Chemical Engineering
Lehigh University


Abstract:

Both colloidal and granular systems may be regarded as model systems that 
demonstrate self-organization.  The combined interactions of discrete 
particles, whose individual properties are relatively well-characterized, 
can result in rich phase behavior and/or pattern formation.  Self-
organization of constituents ranging from millimeter to nanometers in size 
will be demonstrated in two model systems.  In one example, flowing 
granular materials tend to segregate, ordering constituents by size, 
density or even surface properties. Like fluids, chaotic advection in 
granular flows can enhance mixing. We investigate the competition between 
segregation and mixing of glass beads in unique tumbler geometries that 
produce a variety of patterns.  A simple continuum model for the 
underlying flow gives insight into the structure of these segregation 
patterns.  At much smaller length scales, we are interested in self-
organization of particle suspensions in microfluidic channels.  In steady 
pressure-driven flows, self-organization occurs due to particle migration, 
typically driving particles away from the walls toward the center of the 
channel despite the diffusive Brownian motion of the particles. In 
channels whose geometry induces flow in the direction transverse to the 
pressure gradient, competition between particle self-organization and 
mixing due to advection results in concentration profiles where the 
underlying 3D flow acts as a template for the pattern.  

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