Coalescence-induced jumping of droplets on superhydrophobic substrates with a beam structure

Coalescence-induced jumping motion of droplets on superhydrophobic surfaces has potential applications for anti-icing, self-cleaning and anti-fogging, etc. In the present study, the coalescence-induced jumping of mesoscale water droplets on substrate without and with beam is investigated by using many-body dissipative particle dynamics (MDPD) simulations. For the cases of jumping on flat substrate without beam, the jumping velocity scaled by the inertial-capillary velocity (vic) is nearly constant at 0.105 for droplet radius varying from 116.04 nm to 290.10 nm. For coalescence-induced jumping on substrate with a beam, the jumping velocity can be enhanced to 0.7vic, and the jumping is accompanied by the merging process, which is different from that of the droplets merging on substrate without beam. The stages of merging on substrate with a beam can also be divided into 4 stages : I. expansion of liquid bridge; II. detaching from substrate; III. jumping away from beam; IV. moving freely in air. The conversion efficiency of jumping kinetic energy increases with the beam height in the range from zero to the radius of droplet. Hydrophobic and hydrophilic beams lead to coalesced droplets standing on the beam or wrapping the beam. Our work can provide new insights in the droplets coalescence dynamics, and help design water resource collection system and microfluidics devices.