Hypergyrating Droplets Generated on a Selective Laser-Textured Heterogeneous Wettability Surface

 Pan Q, Sun B, Liu W, et al. Hypergyrating Droplets Generated on a Selective Laser-Textured Heterogeneous Wettability Surface[J]. Langmuir, 2020, 36(28): 8123-8128.

Abstract

An impacting droplet on water-repellent surfaces experiences spreading, retraction, and bouncing phases, among which the spontaneous droplets gyrating is very interesting and has promising applications. Here, we present an ultrahigh-speed gyrating droplet generation method via torque transmission on a heterogeneous wettability surface. Hybrid superhydrophobic−superhydrophilic (SH−SHL) patterns were fabricated by selective laser texturing on aluminum alloy substrates. The maximum static contact angles (CAs) of the SH region and SHL region were 163.3 ± 2 and 0 ± 1°, and the advancing and receding CAs were 162.2 ± 1 and 159.9 ± 1°, respectively. The hybrid SH−SHL pattern coupling with the translational kinetic energy of impacting droplet and the rotational momentum of the rotating substrate has been proved as a high-efficiency energy conversion method to construct hypergyrating droplets. A hypergyrating speed exceeding 96700 rpm (13 times of the latest reported value) was achieved in droplets impact on the hybrid SH−SHL-patterned heterogeneous wettability surface, and the maximum energy transformation ratio (α) of the rotating specimen driven torque to the rebounded gyrating droplet is 83.40%. The regulation of the maximum gyrating speed of a bouncing droplet could be controlled by the pattern size and the substrate driving speed, which suggests a practical approach in the energy transformation, a new type of cleaning strategy, and other industrial applications.