Re-touch rebound patterns and contact time for a droplet impacting a superhydrophobic cylinder

Abstract Background Droplet impact on a superhydrophobic cylinder differs from that on a flat surface. After bouncing, once re-touch takes place, the contact time τc would increase, which is unfavorable for some applications. The increased τc may strongly depend on the Weber number and radius ratio, R*, of cylinder to droplet. Methods The impact is investigated via lattice Boltzmann method simulations. The particular emphasis is placed on re-touch rebound patterns and τc. Significant findings Rebound patterns and τc both strongly depend on a combined parameter, α=We/R*, characterizing the asymmetry of droplet spreading and retraction. As α increases, upward rebound and stretched breakup take place sequentially for the first bouncing, whereas rebound patterns change as intact re-touch rebound and separate re-touch rebound for the second bouncing. Increasing α enhances the asymmetry, which promotes the first rebound, thereby reducing τc regardless of rebound patterns. The enhanced asymmetry also accelerates rebound and thus reduces τc in the separate re-touch rebound regime, whereas it hinders rebound, leading to a significantly increased τc. The power-law correlations of τc vs α are developed for the first and second bouncing. Besides, a method is proposed to suppress or prevent the re-touch, which is proven to effectively reduce τc.