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

	             **Monday October 8, 2007**
	
On-chip droplet and particle manipulation by electric fields: 
applications in microfluidics and colloidal assembly

Orlin D. Velev

Dept of Chemical & Biomolecular Engineering
North Carolina State University
 

Abstract:

We will discuss how dielectrophoresis - particle interaction with external 
AC fields - could be used to manipulate and assemble objects of any size. 
Examples involving nanoparticles, microparticles, live cells and droplets 
suspended in water will be presented. We will discuss the interactions 
leading to the assembly of such structures, ways to simulate the dynamics 
of the process, and the effect of particle size and conductivity on the 
type of structure obtained. Two new microfluidic applications will be 
presented. First, we focus on a technique for electric field on-chip 
manipulation of freely suspended droplets. Evaporation from water droplets 
leads to internal liquid circulation and particle microseparation driven 
by Marangoni instabilities. The levitated droplets could serve as 
templates for colloidal assembly, microreactors and containers for 
microbioassays. Second, we demonstrate how miniature semiconductor diodes 
can be engineered into self-propelling micromachines. The diodes suspended 
in water propel themselves electroosmotically in a uniform alternating 
electric field. These "active particles" suggest rudimentary solutions to 
problems facing self-propelling microdevices, such as harvesting power 
from external sources. Semiconductor diodes embedded in channel walls 
could serve as distributed microfluidic pumps and mixers.
 
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