Making superhydrophobic splashes by surface cooling

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 & DEG;C), the splashing behavior 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 behavior, a phenomenon that we relate to ice growth near the contact line. Finally, we show that the transition from hydrophilic to superydrophobic behavior can also be characterized quantitatively on the dynamics of the ejecta.

Automated summary

We experimentally explore the influence of solidification on the splashing phenomenon. By investigating the impact of water drops on dry smooth surfaces, we find that cooling the surface below the liquid melting temperature can greatly reduce the transition velocity to splash. At very low temperatures (below -60°C), the splashing behavior becomes independent of surface undercooling and exhibits similar characteristics as on ambient temperature superhydrophobic surfaces. This similarity is attributed to the increase of the dynamic advancing contact angle of the lamella with surface undercooling, transitioning from isothermal hydrophilicity to superhydrophobic behavior, which is related to ice growth near the contact line. Furthermore, we demonstrate that the transition from hydrophilic to superhydrophobic behavior can be quantitatively characterized based on the dynamics of the ejected droplets.