Tuning the roughness of aluminum surfaces for superrepellency and absorptivity

Superrepellent surfaces are known to be made by surface roughening. However, optimizing roughness solely for non-wetting and low hysteresis, which promotes self-cleaning, typically occurs at a cost to other properties. The other property, considered here as illustrative, is energy absorption from impinging sunlight. Roughness can be tuned for self-cleaning or alternatively for energy absorption, yet the roughness scales for superrepellency and absorptivity do not align cooperatively. Demonstrated here are a twin of simple fabrication methods that tune aluminum surfaces for good self-cleaning and for solar energy absorption. Our results show that superrepellency is favored by roughness scales of microns or smaller alone. On the other hand, roughness of a few microns to tens of microns significantly improves absorption. Our characterizations of surfaces made by the two methods demonstrate how tuning microscale roughness trades superrepellency for absorptivity. The surfaces are robust and the fabrication method is economical. Solar heat harvesting applications may benefit.