Polydimethylsiloxane material as hydrophobic and insulating layer in electrowetting-on-dielectric systems

Open and closed electrowetting-on-dielectric (EWOD) systems based on a spin coated polydimethylsiloxane (PDMS) layer are presented. The PDMS layer acts as both insulation and hydrophobic material. Characterization, through sessile drop experiments, shows the hydrophobic behaviors of the PDMS and saturation of the contact angle at negative bias voltage applied to the droplet. This behavior is ascribed to trapped carrier in the PDMS layer and explains the movement of the droplet toward the grounded electrode found in the EWOD experiments. An electronic board controls all the signals needed for the actuation and sensing functionalities of the EWOD systems. Detection of drop position along the electrode array is successfully achieved by implementing the time-constant method, which evaluates the variation of electrode capacitance induced by the droplet presence on the PDMS surface corresponding to the metal electrode. The microfluidic operations (movement, dispensing and splitting) in both open and closed configurations have been verified and accomplished at voltages around 200 V. © 2014 Elsevier Ltd. All rights reserved.