The post-impact dynamics of drop rebound on inclined hydrophobic surfaces of various wettabilities

In this work, the post-impact drop motions of the rebound regime on inclined hydrophobic surfaces are investigated using a numerical technique. The effects of impact velocity (V-i = 0.5-1.5 m/s), drop diameter (D-0 = 1.0-2.5 mm), surface wettability (theta(eq) = 120 degrees-160 degrees), and inclined angle (alpha = 0 degrees-80 degrees) on the post-impact regimes, contact time (t(c)) and spreading time (t(s)), nondimensionalized maximum spreading diameter (D-s_max*), and drop displacement prior to the rebound (l(d_final)) are examined and analyzed, some of which exhibit markedly different outcomes at alpha = 80 degrees compared to alpha <= 60 degrees. It has been discovered that the rebound regime occurs in most impact conditions at theta(eq) = 160 degrees and 140 degrees but transitions to sliding for all alpha = 80 similar to cases at theta(eq) = 120 degrees. When alpha <= 60 degrees, t(c) and t(s) of theta(eq) = 160 degrees and 140 degrees are very close and hardly affected by V-i and alpha, which are generally smaller than those of alpha = 80 degrees, resulting from the rapid decline of the normal impact velocity that diminishes drop deformation and prolongs drop sliding motion. D-s_max* is barely influenced by theta(eq) but increases with V-i and D-0 and decreases when a increases owing to a greater normal inertial force. l(d_final) generally increases with V-i, D-0, and alpha but with different mechanisms. More importantly, the nondimensionalized parameters t(c)*, D-s_max*, and l(d_final)* are found to scale with the normal or tangential Weber numbers according to the power law, while the exponents vary with theta(eq) and alpha. Published under an exclusive license by AIP Publishing.

Automated summary

In this study, the post-impact drop motions of the rebound regime on inclined hydrophobic surfaces were investigated using a numerical technique. Various influencing factors were examined and analyzed, with significantly different outcomes observed at different incline angles. The nondimensionalized parameters were found to scale with the normal or tangential Weber numbers according to the power law, with exponents varying with surface wettability and inclined angle.