Laplace Pressure Difference Enhances Droplet Coalescence Jumping on Superhydrophobic Structures

Coalescence-induced droplet jumping has great prospects in manyapplications. Nevertheless, the applications are vastly limited by a low jumping velocity.Conventional methods to enhance the droplet coalescence jumping velocity areenabled by protruding structures with superhydrophobic surfaces. However, thejumping velocity improvement is limited by the height of protruding structures. Here,we present rationally designed limitation structures with superhydrophobic surfaces toachieve a dimensionless jumping velocity,Vj*approximate to 0.64. The mechanism of enhancing thejumping velocity is demonstrated through the study of numerical simulations andgeometric parameters of limitation structures, providing guidelines for optimizedstructures. Experimental and numerical results indicate that the mechanism consists ofthe combined action of the velocity vectors'redirection and the Laplace pressuredifference within deformed droplets trapped in limitation structures. On the basis ofprevious research on the mechanisms of protruding structures and our study, wesuccessfully exploited those mechanisms to further improve the jumping velocity by combining the limitation structure with theprotruding structure. Experimentally, we attained a dimensionless jumping velocity ofVj*approximate to 0.74 with an energy conversionefficiency of eta approximate to 48%, breaking the jumping velocity limit. This work not only demonstrates a new mechanism for achieving a highjumping velocity and energy conversion efficiency but also sheds lights on the effect of limitation structures on coalescencehydrodynamics and elucidates a method to further enhance the jumping velocity based on protruding structures.

Automated summary

Coalescence-induced droplet jumping has great prospects in many applications but is hindered by a low jumping velocity. This study presents rationally designed limitation structures with superhydrophobic surfaces to achieve a higher jumping velocity. Through experimental and numerical analysis, the mechanism of enhancing the jumping velocity is explained and a method combining limitation structures with protruding structures is proposed to further improve the jumping velocity.