Nanopatterned Metallic Surfaces: Their Wettability and Impact on Ice Friction

A distinct surface microstructure was created on the surface of metal alloys and highly pure metals by using a one-step femtosecond laser process. After irradiation the surfaces show initially superhydrophilic behavior with complete wetting. With time and exposure to ambient air, however, the measured contact angles on these surfaces increase significantly. Eventually, all surfaces become hydrophobic and support Cassie-like hydrophobicity with contact angles beyond 150 degrees and very low hysteresis. The increase in contact angle with time correlates with the amount of carbon detected on the irradiated surface, which suggests that the time dependency of the surface wettability depends on the combined effect of surface morphology and surface chemistry. The nanopatterned superhydrophobic substrates were tested in ice friction tests. At temperatures close to the melting point and relatively high speeds of the metal slider, the laser created nanoroughness and hydrophobicity significantly decrease ice friction. This decrease in friction is attributed to the suppression of capillary bridges between the slider and ice surface, which contributes considerably to the overall frictional resistance.