Asymmetric dynamic response of droplet impact on wedge microgrooved substrates

The phenomenon of droplet impact on surfaces with asymmetric structures is widely observed in both natural and industrial environments. Designing surface structures can effectively promote droplet detachment and asymmetric dynamic responses. This work investigates the dynamic behavior and rebound of droplets impacting a wedge-shaped grooved substrate with two types of asymmetric features through molecular dynamics simulation. The results indicate that the two geometric asymmetries of the substrate—the directional asymmetry along and perpendicular to the grooves, and the asymmetry of the groove cross-sectional shape—lead to two distinct asymmetric behaviors after impact: asymmetric spreading–retraction dynamics and asymmetric rebound behavior. The spreading behavior in both directions during droplet impact exhibits asymmetric characteristics and a competitive relationship. These trends vary with changes in the surface structure, and a theoretical model is further proposed to compare the effects of surface geometry and Weber number on the ratio of maximum spreading in the two directions. This asymmetric behavior is illustrated through calculations of spreading factor and pancake bounce quality. The contact time was shown to be independent of We but influenced by the surface structure geometry, which significantly reduced the contact time by up to 67%, and a theoretical analysis was provided to explain the roles of the two factors. Additionally, the droplet rebound angle and velocity are calculated, demonstrating that capillary pressure plays a major role in droplet rebound and effectively reflects the rebound direction.