Spontaneous movement of water droplets on patterned Cu and Al surfaces with wedge-shaped gradients

Abstract

We report a simple technique for moving water droplets on a hydrophilic aluminum surface containing a hydrophobic copper background. A surface tension gradient due to a triangular-shaped wedge moves the droplets towards the end of the wedge which contains more Al surface area. Movement on both horizontal surfaces and surfaces oriented vertically against gravity has been observed. The mode of droplet motion was found to depend on the wedge angle, and the speed was found to depend on both the wedge angle and the droplet contact angles on the Al and Cu. © 2013 AIP Publishing LLC.