Effect of Surface Uniformity and Droplet Volume on Actuation Voltage of PCB Based EWOD Microfluidic System

Electrowetting on Dielectrics (EWOD) is an important method of manipulating discrete fluid droplets in digital microfluidic systems. In this paper, a simply implemented low cost EWOD system based on printed circuit board was built and tested. The form of the triple contact line (TCL) connecting the droplet with solid surface and ambient surrounding was simulated using a numerical simulation tool called Surface Evolver (SE). Different electrode patterns and sizes were designed and measurements were conducted using deionized (DI) water mixed with Sodium Chloride (NaCl) as fluidic samples. Polytetrafluoroethylene (PTFE), Parylene C and Parafilm were used as dielectric layers separating microfluidic droplets from the electrodes surface. In addition, these materials provided a hydrophobic surface leading to an increase in the initial contact angle of the droplets. The actuation voltage of the system varied between 40 V and 183 V depending on the electrodes pattern and size and the volume of the droplets. The smoothness and regularity of the PCB and hydrophobic surfaces had a major effect on decreasing the actuation voltage of the system.