Directional rebound control of droplets on low-temperature regular and irregular wrinkled superhydrophobic surfaces

The directional rebound control of droplets is of great significance in many industrial applications, such as anti-icing, self-cleaning and microfluidics devices. Various strategies of droplets directional transport have been studied at room temperature and high temperature. However, it is still a challenge to control the rebound direction of droplets without external forces at low temperature and condensation conditions, where the droplets transit to Wenzel state. Herein, two kinds of graphene-based wrinkled superhydrophobic films with regular high-low structures (RSGF) and irregular spiral structures (ISGF) are prepared. The droplets on the films are still in the Cassie state by adjusting the size of the microstructure at low temperature. More importantly, the experimental and numerical simulation results reveal that the regularity of wrinkled structures can be used to adjust the distribution of viscous forces between film and droplets, which can control the direction of droplets rebound force. On the RSGF, the impacting droplets can retract symmetrically and rebound along the vertical direction; while on the ISGF, the droplets retract asymmetrically due to the irregular spiral microstructure and the rebound direction is shifted in the fixed direction.