Prompting Splash Impact on Superamphiphobic Surfaces by Imposing a Viscous Part

It is widely acknowledged that splash impact can be suppressed by increasing the viscosity of the impinging drop. In this work, however, by imposing a highly viscous drop to a low‐viscosity drop, it is demonstrated that the splash of the low‐viscosity part of this Janus drop on superamphiphobic surfaces can be significantly promoted. The underlying mechanism is that the viscous stress exerted by the low‐viscosity component drives the viscous component moving in the opposite direction, enhancing the spreading of the low‐viscosity side and thereby its rim instability. The threshold velocity, above which splashing occurs, can be tuned by varying the viscosity ratio of the Janus drop. Moreover, the impact of the Janus drop can be employed to verify the mechanism of splash. When a single‐phase water drop impacts on a superamphiphobic surface, it symmetrically spreads and completely bounces off the surface. Surprisingly, by imposing a highly viscous drop to the water drop, the resulted Janus drop exhibits an asymmetric spreading and retracting phase, and the splashing of the water part is significantly promoted compared to the single‐phase water drop impact.