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Jame's Project Page - RISE Summer 2008 |
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Intern: James Helton, Chemical Engineering, Arizona State University
Mentor: Andrew Pascall
Faculty Supervisor: Todd Squires
Department: Chemical Engineering |
INDUCED CHARGE ELECTRO-OSMOSIS OVER DIELECTRIC THIN FILMS
Advances in technology are making compact microfluidic devices possible for biological and chemical applications.
Microfluidic devices allow one to integrate several different functions on to a single chip, for example, capillary
electrophoresis, isoelectric focusing and microfluidic pumps. One way of manipulating fluids in these devices is to
use electric fields. Induced Charge Electro-osmosis (ICEO) occurs when an AC electric field is applied across the
channel which results in the formation of a polarized electric double layer at the surface of the metal. The fluid will
move toward the electrode in both directions creating two recalculating patterns. The electrode was fabricated on a
quartz substrate using basic photolithography techniques. The polydimethylsiloxane (PDMS) channels are patterned
using soft lithography on an etched Si wafer. The channel used in this experiment is one side quartz and three sides
PDMS both of which do not affect the electric field. The fluid is a solution of KCl and 500nm fluorescent
polystyrene beads. The beads are added to the electrolyte, which will trace the planar velocity of liquid at surface of
the electrode. Particle image velocimetry (PIV) was used to determine flow velocity. Velocities in a 60 µm/second
range were measured. A nonconducting dielectric layer placed over the conductor is used to test how it will affect
the fluid, which theory predicts will decrease the velocity. The result showed that a dielectric thickness of 100µm
reduced the velocity by 15µm/s and correlated with the theoretical calculations.
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