Ultrafast laser hybrid fabrication of hierarchical 3D structures of nanorods on microcones for superhydrophobic surfaces with excellent Cassie state stability and mechanical durability

Superhydrophobic surfaces have been attracting considerable attention due to potential applications in self-cleaning, anti-icing, water/oil separation, drag reduction, water collection, etc. However, to date, except for a few textile surfaces and coating products, only a limited number of superhydrophobic applications have been commercialized. The main reasons for the limited number of applications are attributed to the poor Cassie state stability and inadequate mechanical durability of superhydrophobic surfaces. Although numerous efforts have been invested to improve the Cassie state stability or mechanical durability of such surfaces, the surfaces with both acceptable Cassie state stability and mechanical durability have been rarely reported. In the present study, a 3D hierarchical structure composed of nanorods on periodically structured microcones was fabricated on a copper surface by an ultrafast laser-chemical hybrid method. The effect of microcone heights of the proposed structures on the Cassie state stability and mechanical durability was investigated. It is demonstrated that Cassie state stability of the manufactured surfaces could be improved efficiently by increasing the microcone height. However, when the height of the microcone gets to a certain magnitude (e.g., 50 mu m in present study), a further increase of microcone height has a little influence on the stability of the Cassie state. The mechanical durability study shows that the superhydrophobic surface with the optimal microcone height could withstand 500 tape peeling cycles in a tape peeling test, 4 abrasion cycles in a linear abrasion test, and 35min of water flow impact, before the contact angle decreases to 150 degrees and the sliding angles increase to 10 degrees, indicating good mechanical durability. Our proposed structures with both great Cassie state stability and mechanical durability could be promising candidates for many potential applications such as for solar cells, infrared sensors, and some space-related equipment, among others.