Wettability-regulated dynamics of floating spheres: From jet entrapment to inertial repulsion

The attachment of a liquid jet to a convex surface is a well-established phenomenon that typically results in fluid adherence. This study reports a distinct regime demonstrating that the wettability of the floating curved surface is a key parameter determining whether the impinging jet and the curved surface undergo attraction or repulsion. On the hydrophilic sphere, flow attachment creates a restoring force that traps and centers the sphere beneath the jet. Conversely, the superhydrophobic sphere induces rapid fluid rebound and reflection, which inverts the momentum transfer and generates a significant repulsive force. Experimental analysis using high-speed imaging and force measurements reveals that this superhydrophobic repulsion is governed by the jet's impact location and inertial momentum flux. Theoretical models based on elastic collision and momentum conservation are derived, which agree with the experiments. These findings identify superhydrophobicity as a passive mechanism for the manipulation of the motion of floating objects.