EWOD-aided droplet transport on texture ratchets

We report a digital microfluidic device to transport aqueous droplets on an open surface in air using electrowetting-on-dielectric (EWOD) with anisotropic ratchet conveyors (ARCs). ARCs are micro-sized periodic semicircular hydrophilic regions on a hydrophobic background, providing anisotropic wettability. SiN_x and Cytop are used as the dielectric layer between the water droplet and working electrodes. By adopting parylene as a stencil mask, hydrophilic patterning on the hydrophobic Cytop thin film layer is achieved without the loss of Cytop hydrophobicity. While the traditional EWOD platform requires the control of multiple electrodes to transport the droplet, our system utilizes only two controlling electrodes. We demonstrate that 15 μl water droplets are transported at a speed of 13 mm/s under 60 V_peak sinusoid AC signal at 50 Hz. Droplet transport at 20 Hz is also presented, demonstrating that the system can operate within a range of frequencies.