<p>This study explores the asymmetric bouncing dynamics of a binary drop with viscosity contrast on the inner surfaces of cylinders decorated with a circumferential ridge. The drop consists of a low-viscosity water phase and a high-viscosity glycerin–water mixture, forming an internal interface oriented perpendicular to the ridge. Using Volume of Fluid simulations, this study analyzes the effects of surface curvature, viscosity ratio, and Weber number on retraction behavior and separation of the low-viscosity component. Two distinct retraction modes are identified: bi-directional retraction, in which the film retracts symmetrically in both axial and azimuthal directions, and uni-directional retraction, dominated by axial collapse. A regime map reveals that separation occurs above a critical threshold, accompanied by a transition from bi-directional to uni-directional retraction. The dimensionless residence time of the low-viscosity phase follows distinct scaling laws for each retraction mode. Theoretical predictions based on retraction dynamics are consistent with simulation results and provide a clear interpretation of the underlying mechanisms. These findings demonstrate that both geometric confinement and viscosity contrast play critical roles in dictating asymmetric momentum redistribution and drop separation, offering a framework for the design of hybrid-fluid systems for selective liquid handling.</p> Graphical abstract <p>This study highlights the importance of curvature in determining the retraction pathway: while higher curvature promotes symmetriccollapse and reattachment, lower curvature favors uni-directional retraction and efficient drop breakup.</p> <p></p>