Extreme resistance of super-hydrophobic surfaces to impalement: reversible electrowetting related to the impacting/bouncing drop test

TL;DR

This study demonstrates that super-hydrophobic silicon nanowire surfaces exhibit exceptional resistance to impalement, with thresholds surpassing 35 kPa, and reveals a correlation between electrowetting and impact resistance, highlighting structural factors that enhance durability.

Contribution

It establishes a link between electrowetting and impact resistance in super-hydrophobic nanowire surfaces, showing how structural modifications improve impalement thresholds and reversibility.

Findings

Impalement thresholds exceed 35 kPa on robust surfaces.

Increasing nanowire length and density raises impalement thresholds.

Contact-angle hysteresis decreases after impalement, indicating partial impalement.

Abstract

The paper reports on the comparison of the wetting properties of super-hydrophobic silicon nanowires (NWs), using drop impact impalement and electrowetting (EW) experiments. A correlation between the resistance to impalement on both EW and drop impact is shown. From the results, it is evident that when increasing the length and density of NWs: (i) the thresholds for drop impact and EW irreversibility increase (ii) the contact-angle hysteresis after impalement decreases. This suggests that the structure of the NWs network could allow for partial impalement, hence preserving the reversibility, and that EW acts the same way as an external pressure. The most robust of our surfaces show a threshold to impalement higher than 35 kPa, while most of the super-hydrophobic surfaces tested so far have impalement threshold smaller than 10 kPa.