Making superhydrophobic splashes by surface cooling

TL;DR

This study demonstrates that cooling surfaces below the melting point of water significantly reduces splash velocity and induces superhydrophobic-like behavior due to increased contact angles, with implications for controlling splashing.

Contribution

It reveals that surface cooling below freezing induces a transition to superhydrophobic-like splashing behavior, linked to increased dynamic contact angles influenced by crystal formation.

Findings

Splash transition velocity decreases with surface cooling.

At temperatures below -60°C, splashing mimics superhydrophobic surfaces.

Crystal formation affects the dynamic contact angle of the lamella.

Abstract

We study experimentally the enhancement of splashing due to solidification. Investigating the impact of water drops on dry smooth surfaces, we show that the transition velocity to splash can be drastically reduced by cooling the surface below the liquid melting temperature. We find that at very low temperatures (below $-60 ^\circ \rm C$), the splashing behaviour becomes independent of surface undercooling and presents the same characteristics as on ambient temperature superhydrophobic surfaces. This resemblance arises from an increase of the dynamic advancing contact angle of the lamella with surface undercooling, going from the isothermal hydrophilic to the superhydrophobic behaviour. We propose that crystal formation can affect the dynamic contact angle of the lamella, which would explain this surprising transition. Finally, we show that the transition from hydrophilic to superydrophobic behaviour can also be characterized quantitatively on the dynamics of the ejecta.