Experimental study on water entry of Janus spheres with asymmetric wettability

This study focused on the water entry of Janus spheres with asymmetric wettability. The effects of impact velocity and sphere size on splash behaviors, cavity dynamics, and trajectory deviations are experimentally investigated using high-speed imaging techniques. Experimental results demonstrate that wettability contrast drives distinct contact-line dynamics, resulting in three-phase line pinning and sliding behavior that generates pronounced asymmetry in the splash curtain. Enhanced rupture occurs on hydrophilic surfaces while splash height attenuates with rising velocity. Cavity formation demonstrates profound asymmetry, redirected toward hydrophilic hemispheres by orthogonal pressure gradients established through divergent contact-line motion and Marangoni flows. By converting kinetic energy into tangential momentum, implosion energy reversal drives transverse jetting at hydrophobic interfaces. Heterogeneous wettability preserves inertial scaling of cavity pinch-off times. Resultant hydrodynamic attraction asymmetries mediate trajectory deviation toward hydrophilic regions, with deflection trajectory scaling with impact velocity. The findings establish wettability patterning as a mechanism for passive trajectory control through engineered flow separation.