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Electrohydrodynamic modeling of microdroplet motion in digital microfluidic systems

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Title: Electrohydrodynamic modeling of microdroplet motion in digital microfluidic systems
Author: Ahmadi, Ali
Degree Doctor of Philosophy - PhD
Program Mechanical Engineering
Copyright Date: 2011
Publicly Available in cIRcle 2011-09-30
Abstract: Digital microfluidic devices provide a new technology platform for controlled motion of small volumes of fluid. These systems can provide high speed microdroplet transport on integrated electrode arrays. The generic nature of these electrode architectures offers versatility, scalability, and reconfigurability that is crucial for biomedical, chemical, and sensing applications. The structural layout of digital microfluidic devices and the employed electrical activation schemes must be considered together in the design and operation of successful fluid actuation. Microfluidic models provide an effective tool for predicting this device performance and optimizing parameters to achieve high efficiency. Numerical simulation of the electrodynamics of microdroplet motion in digital microfluidic systems will provide better understanding of the effects of electrode shape on actuation forces, actuation voltage/frequency and liquid properties (e.g., conductivity, permittivity, and surface tension) on microdroplet actuation. However, the development of such models is far from trivial as many complex physicochemical phenomena become involved in the transport. In this thesis, a novel numerical multiphysic approach is used to model the microdroplet motion in digital microfluidic systems. The actuation force in the system of the interest is provided by applying voltage to the underlying electrodes. The main focus of this study is on the conductive liquids, however the electromechanical approach used in this research can be readily extended to dielectric liquids. The proposed model employs an electrohydrodynamic approach for estimating the driving, wall and filler forces. Additionally, the effects of the evaporation are considered from two aspects: it is shown that an additional force is needed to balance the dynamic equation of the microdroplet motion, and the microdroplet interface is deformed due to the change in the microdroplet radius. Finally, the effects of the biomolecular adsorption are included by adding a new force to the dynamic equation of the microdroplet motion, and the adsorption rate is then related to the change in the interfacial tensions and the capacitance of the underlying layers. The results of the developed model are presented and verified with experimental data obtained from literature, and it is shown that the model provides an accurate representation of microdroplet transport in digital microfluidic systems.
URI: http://hdl.handle.net/2429/37731
Scholarly Level: Graduate

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