| In microscale world, surface tension is dominant over the body force, such as gravity or inertia. As the microfluidics research advances rapidly, research interest in surface phenomena grows accordingly. Especially, controlling the surface tension by various surface phenomena has been studied by many research groups. In this dissertation, we present a useful method to control surface tension--electric control of surface tension (electrowetting) at the solid-liquid interface. More specifically, we focus on electrowetting on a solid surface covered with a dielectric layer, or EWOD.; Electrowetting has been known for more than 100 years, however, in its traditional configuration, it has several drawbacks when used for microfluidics: It small force, limited choice of electrode materials and liquids, lack of reversibility in the motion by electrowetting, and so on. We chose electrowetting-on-dielectric (EWOD) in developing microfluidic devices to overcome the problems associated with traditional electrowetting by using a thin dielectric layer on the surface of electrode. The goal of our research is to develop a pumpless and valveless liquid handling method that is also free from problems of high electric field, electrochemical reactions, and high energy consumption, yet capable of achieving a high degree of freedom in liquid manipulation.; We first report basic studies of the EWOD phenomena, expanded to study how to reduce the high voltage requirement of EWOD compared with traditional electrowetting. We also report a study of surface roughness related to EWOD. We show how to take advantage of rough surfaces in EWOD devices. Based on the study of EWOD physics, modeling and basic functions of microfluidics, we subsequently developed EWOD-driven microfluidic sample preparation chips for matrix assisted laser desorption/ionization mass spectrometry (MALDI-MS). |
