Low-cost Polyurethane Coating as Dielectric Component in Digital Microfluidics

Digital microfluidics (DMF) as a platform for precise handling of liquid droplets is a powerful tool but the affordability of the device has been one of the hindrances to its wide implementation. This paper reports the development of DMF devices using low-cost materials and simple deposition techniques specifically for the device dielectric component. Three commercial polyurethane coatings were investigated for their feasibility as the dielectric layer. The electrowetting behaviour of these materials was investigated by evaluating the change in contact angle with applied voltage of a water droplet sitting on the dielectric samples prepared using easy deposition methods such as spraying and spin coating. Devices were then fabricated using these materials to evaluate their capability to actuate droplets. Five types of polyurethane dielectric sample exhibited contact angle reversibility with hysteresis ranging between 4° to 25° after 250 VDC application. Droplet transportation back and forth across 8 electrodes at 180 VRMS has been demonstrated in a device made of one of the polyurethane coatings using a spraying technique. This result implies the potential of using polyurethane for future development of low-cost and disposable DMF devices.