A Master of Science thesis in Mechanical Engineering by Malik Mamoun Al-Lababidi entitled, “Droplet Geometry and Device Configuration Effects on Droplet Actuation in Open Digital Microfluidics”, submitted in December 2021. Thesis advisor is Dr. Mohamed Abdelgawad. Soft copy is available (Thesis, Completion Certificate, Approval Signatures, and AUS Archives Consent Form).
Abstract
Digital microfluidics (DMF) is the manipulation of liquid droplets over an array of micro electrodes. It is considered as a new technology that facilitate several applications such as chemical synthesis, biological assays, and electronics cooling. Determination of droplet actuation forces is essential in DMF analysis to ensure fast and reliable droplet motion. This thesis demonstrates the origin of these electrical actuation forces and investigates the parameters that affect these forces. In addition, different approaches to calculate actuation forces are explored. In most previous studies, droplets actuation forces on open digital microfluidic devices were calculated using the capacitive energy approach, whereas this thesis implements numerical modeling using COMSOL Multiphysics to calculate the electrical forces generated on a droplet based on the Maxwell stress tensor. The different investigated parameters are droplet volume, droplet contact angle, electrode shape, and grounding configuration. It has been found that droplets with large volumes and small contact angles experience highest actuation forces. Both droplet volume and contact angle decide the droplet base radius which should be large and far enough from the high electric field intensity region at rear of the actuated electrode to avoid generating any backward forces. The best studied electrode shape for droplet actuation was the pinned electrodes with a pin radius of 0.6 mm for a 28 μL droplet. However, square electrodes with all-ground configuration had the highest actuation force average (39.04 μN) for the 48 μL droplet. In general, having substantial grounding surrounding the droplet enhances actuation forces. A summary of all simulated models with different droplet volumes, contact angles, electrode shape, and grounding configuration was tabulated.