Digital microfluidics is a promising fluid processing technology used in lab-on-achip applications to perform chemical synthesis, particle filtration, immunoassays, and other biological protocols. Traditional digital microfluidic (DMF) devices consist of a 2D grid of coated electrodes over which droplets are manipulated. Selective activation of the electrodes results in an electrowetting effect that deforms the droplets and can move them around the electrode grid. More recently, electrowetting on dielectric has also been used to eject droplets and transfer them between opposing surfaces. This has given rise to new 3D DMF devices capable of more sophisticated routing patterns that can minimize crosscontamination between different biological reagents used during operation. A better understanding of electrowetting-induced droplet ejection is critical for the future development of efficient 3D DMF devices. The focus of this work was to better predict electrowetting-induced droplet ejection and to determine how droplet selection and electrode design influence the process. An improved model of droplet gravitational potential and interfacial energy throughout ejection was developed that predicts a critical electrowetting number necessary for successful detachment. Predictions using the new model agreed more closely with experimentally observed thresholds than previous models, especially for larger droplet volumes. Droplet ejection experiments were also performed with a variety of coplanar electrode designs featuring different numbers of electrode pieces and different spacings between features. The critical voltage for ejection was observed to be approximately the same for all designs, despite the poor predicted performance for the case with the widest spacing (200 𝜇𝑚) where nearly 25% of the area beneath the droplet was dead space. Findings indicated that a critical electrowetting for ejection must be achieved at the contact line of a droplet rather than over the entire droplet region. Droplets were also ejected for the first time from devices with inkjet-printed electrodes, demonstrating the feasibility of future low-cost 3D DMF systems.
Library of Congress Subject Headings
Microfluidic devices--Design and construction; Electrostatic atomization; Spraying--Equipment and supplies
Department, Program, or Center
Burkhart, Collin Taylor, "Coplanar Electrowetting-Induced Droplet Ejection for 3D Digital Microfluidic Devices" (2021). Thesis. Rochester Institute of Technology. Accessed from
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