Pushing or pulling droplets on ZnO nanorods with an UV light

Water droplets were either pushed or pulled with an UV light on the surface of vertically aligned and superhydrophobic ZnO nanorods (NRs). The contact angle of the droplets reduce to a lower value due to the absorption of UV by ZnO NRs and a circulating current was observed inside the droplet. The droplets were either pushed away from or pulled toward to the center of the UV light depending on the locations of the droplets to the UV light. It is obvious that in the pushing mode, the circulating current dominate the direction of the movement of the droplets, while in the pulling mode, the contact angle change dominate the direction of the droplet movement