Thesis Abstract and Dissertation Abstracts
Electrowetting Phenomenon for Microsized Fluidic Devices
Abstract Category: Engineering
Course / Degree: n/a
Institution / University: Tufts University, United States
Published in: 2008
This work reports on experiments conducted to evaluate the electrowetting phenomenon as a potential method to manipulate and transport liquids for microfluidic applications. The work was a two-part effort which consisted of 1) fundamental experiments to study critical phenomenological aspects of electrowetting and 2) the implementation of electrowetting controlled liquid interfaces in micro-sized fluidic devices.
One of the fundamental investigations carried out was a study of the contact angle saturation phenomenon. Contact angle saturation is the condition when no additional observed contact angle change occurs for increases in applied potential. The major finding from the study was that contact angle saturation is independent of the electric field intensity and is reached when the surface energy between the aqueous-solid interface approaches zero energy. During this investigation an effort was also made to reduce the voltage required to generate significant contact angle change. Through the use of surfactants added to the aqueous phase and by processing a thin, high quality dielectric layer, a remarkable contact angle change of 100º for an applied potential less than 3 V was demonstrated.
A second fundamental investigation looked at reversibility issues associated with repeated voltage actuations. Experiment results indicated that irreversible trapped charge may accumulate at the aqueous-solid interface which gives rise to contact angle relaxation. The accumulation of trapped charge was found to be related to the applied electric field intensity and breakdown strength of the fluoropolymer. As a result a voltage threshold exists for the onset of irreversible electrowetting which was correlated to the effective electric field intensity matching the breakdown strength. Experiments conducted with potentials above the voltage threshold resulted in contact angle relaxation, and experiments conducted with potentials below the voltage threshold, showed no signs of irreversible electrowetting behavior.
In the second phase of this research effort microfluidic devices were fabricated that used electrowetting to control liquid transport. The devices fabricated consisted of drop generators, micropumps, and other test devices designed to study electrowetting performance within fully enclosed micro-structures. This work has lead to several new developments including novel fabrication techniques for enclosed micro-channel structures, and a robust liquid integration system. In addition the electrowetting based micropumps demonstrated that pumping systems can be designed to not only manipulate individual drops but, by using a liquid interface to act as a piston and valve, can produce semi-continuous flow. These micropumps produced pressure differences on the order of kilo- Pascals and generated flow rates on the order nanoliters per second.
Thesis Keywords/Search Tags:
electrowetting, microfluidic, contact angle saturation, electrowetting reliability, micropumps, microvalves, drop generators
This Thesis Abstract may be cited as follows:
S. Berry, Electrowetting Phenomenon for Microsized Fluidic Devices, PhD thesis, Tufts University, 2008
Submission Details: Thesis Abstract submitted by Shaun Berry from United States on 17-Feb-2009 00:34.
Abstract has been viewed 3752 times (since 7 Mar 2010).
Shaun Berry Contact Details: Email: sberry@LL.mit.edu
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