Bouncing feature of Janus drops on superhydrophobic convex cylindrical surfaces with a ridge structure

This study investigates the collision dynamics of Janus drops on superhydrophobic convex cylindrical surfaces decorated with a ridge, using three-dimensional volume-of-fluid simulations. The Janus configuration includes a viscosity-contrasted binary system of water (W) and glycerin–water mixture (G), forming a stable fluid interface. Key parameters including surface curvature, viscosity ratio, and Weber number (We) were systematically varied to elucidate their roles in separation dynamics and residence time. Simulation results reveal that increasing curvature enhances circumferential asymmetry and promotes earlier separation, and a higher viscosity ratio facilitates directional retraction and reduces the We threshold for detachment. A regime map demonstrates that ridged surfaces enable separation at significantly lower We compared to ridge-free counterparts. To quantify retraction behavior, a theoretical model is developed by incorporating anisotropic spreading lengths, yielding a residence time scaling with We and normalized curvature of the cylinder, in close agreement with simulation data. Momentum analysis further confirms that circumferential motion of the W part drives efficient phase separation and shortened residence time. These findings highlight the synergistic effects of ridge geometry and internal viscosity contrast in tuning multiphase rebound behavior, offering design insights for advanced fluid–surface interaction control.