Janus drop impact on inclined non-wettable ridged surface

The impact dynamics of Janus drops on inclined non-wettable ridged surfaces are systematically investigated using numerical simulations and theoretical models. The Janus configuration comprises two immiscible phases: a low-viscosity water part (W) and a high-viscosity glycerin–water solution part (G), with a stable interface. The combined effects of viscosity ratio, impact inertia, and surface inclination on separation behavior are analyzed by varying the normal (Wen) and tangential (Wet) Weber numbers. Higher viscosity ratios suppress tangential retraction of the G part, promoting asymmetric lateral retraction of the W part and facilitating separation. Regime maps are constructed for different viscosity ratios, presenting the separation conditions as functions of Wen and Wet. The normal Weber number primarily controls residence time by setting the initial spreading extent, while the tangential Weber number generates the morphological asymmetry (tangential deformation) that drives separation. Furthermore, a theoretical retraction model is developed to predict the residence time and demonstrates strong agreement with simulation results. This combined framework offers predictive understanding of Janus drop splitting dynamics and provides design guidelines for applications requiring efficient phase separation.