A 'splash' is usually heard when a solid body enters water at large velocity.This phenomena originates from the formation of an air cavity resulting fromthe complex transient dynamics of the free interface during the impact. Theclassical picture of impacts on free surfaces relies solely on fluid inertia,arguing that surface properties and viscous effects are negligible atsufficiently large velocities. In strong contrast to this large-scalehydrodynamic viewpoint, we demonstrate in this study that the wettability ofthe impacting body is a key factor in determining the degree of splashing. Thisunexpected result is illustrated in Fig.1: a large cavity is evident for animpacting hydrophobic sphere (1.b), contrasting with the hydrophilic sphere'simpact under the very same conditions (1.a). This unforeseen fact isfurthermore embodied in the dependence of the threshold velocity for airentrainment on the contact angle of the impacting body, as well as on the ratiobetween the surface tension and fluid viscosity, thereby defining a criticalcapillary velocity. As a paradigm, we show that superhydrophobic impacters makea big 'splash' for any impact velocity. This novel understanding provides a newperspective for impacts on free surfaces, and reveals that modifications of thedetailed nature of the surface -- involving physico-chemical aspects at thenanometric scales -- provide an efficient and versatile strategy forcontrolling the water entry of solid bodies at high velocity.
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