The arrowed surface ratchets with hydrophobic parylene for droplet transportation

In this article we demonstrated a way to transport droplets by an arrowed micro-pillar array surface with hydrophobic parylene. We developed successfully that the lightly hydrophilic parylene surface can be changed to hydrophobic one treated with fluorine-based plasma (CF4 and SF6) for 10 seconds. Otherwise, we designed the ratchet pattern similar to the one proposed by A. Shasty in 2007. The droplet can be up or back transported by advancing or recessive arrowed surface ratchets, and the average velocity is 23 mm/sec. Moreover, we also compared the case modified by hexamethyldisilazane (HMDS) vapor and showed the better performance of our work.