Abstract
In many electrowetting on dielectric (EWOD) based microfluidics devices, droplet actuation speed is a crucial performance-controlling parameter. Our present study aims to characterize and study droplet speed in a typical EWOD device. First, a practical droplet speed measurement method has been methodically demonstrated and some related velocity terms have been introduced. Next, influence of electrode shape on droplet speed has been studied and a new design to enhance droplet speed has been proposed and experimentally demonstrated. Instead of using square shaped electrodes, rectangular electrodes with smaller widths are used to actuate droplets. Additionally, different schemes of activating electrodes are studied and compared for the same applied voltage. The experiments show that a particular scheme of activating the array of rectangular electrodes enhances the droplet speed up to 100% in comparison to the droplet speed in a conventional device with square shaped electrodes.
Highlights
In recent years, significant efforts have been devoted to the development of droplet-based lab-on-a-chip devices of which advantages include being programmable and reconfigurable
According to the rigid body model considered by Chatterjee et al [25], and Bahadur and Garimella [21], both the droplet actuation force and the opposing forces during motion influence the droplet dynamics, which depend on the shape of the droplet base area
Since tmin is unique for each case, different switching times were tested for a droplet to move over a distance of 16 mm
Summary
Significant efforts have been devoted to the development of droplet-based lab-on-a-chip devices of which advantages include being programmable and reconfigurable. Basic droplet handling techniques—droplet dispensing, transporting, merging and splitting—can be done by sequentially activating and deactivating specific electrodes, which allows to address each droplet individually and to perform various unit processes, such as encapsulation [7], mixing [8], extraction [9,10] and separation [9] in lab-on-a chip devices All of these applications are limited to mostly parallel plate EWOD device. The review article by Mugele and Baret [6] discussed approaches to understand the electrowetting theory applicable for low voltages They analyzed the origin of electrostatic forces that reduce the apparent contact angle and induce droplet motion.
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