Larsen, Simon Tylsgaard3; Andersen, Nis Korsgaard1; Søgaard, Emil1; Taboryski, Rafael J.1
1 Department of Micro- and Nanotechnology, Technical University of Denmark2 Polymer Micro & Nano Engineering, Department of Micro- and Nanotechnology, Technical University of Denmark3 Risø National Laboratory for Sustainable Energy, Technical University of Denmark
We study water drop roll-off at superhydrophobic surfaces with different surface patterns. Superhydrophobic microcavity surfaces were fabricated in silicon and coated with 1H,1H,2H,2H-perfluorodecyltrichlorosilane (FDTS). For the more irregular surface patterns, the observed increase in roll-off angles is found to be caused by a decrease of the receding contact angle, which in turn is caused by an increase of the triple phase contact line of the drops for those more irregular surfaces. To understand the observation, we propose to treat the microdrops as rigid bodies and apply a torque balance between the torque exerted by the projected gravity force and the torque exerted by the adhesion force acting along the triple line on the receding side of the drop. This simple model provides a proper order of magnitude estimate of the measured effects.