Bioinspired preparation of regular dual-level micropillars on polypropylene surfaces with robust hydrophobicity inspired by green bristlegrass leaves

The fine microstructure on the natural green bristlegrass leaf of Setaria viridis (L.) Beauv, which exhibits a contact angle (CA) of 155 degrees +/- 2 degrees and a rolling angle (RA) of 79 degrees +/- 2 degrees, is carefully observed. Based on the understanding of the underlying mechanisms for superhydrophobicity and moderate surface adhesion, an efficient replica molding strategy is proposed for mimicking the microstructures on green bristlegrass leaf surface to polypropylene (PP) surfaces. The bioinspired PP replica with dual-level micropillars are molded by using the unitized template of steel Meshes A and B. Interestingly, the PP replica inherits both hydrophobicity and adhesion of the natural leaf. Furthermore, the PP replica can stabilize its hydrophobic state under a 980 Pa external pressure, which is attributed to the composite Cassie-Wenzel mixed wetting state on the microstructured interface. The CA comparatively goes down and RA increases, resulting in superhydrophobic surface with moderate adhesion on the bioinspired surface. Hence, the microstructures and hydrophobicity are successfully replicated to the PP surface by only using the low cost, available and reliable steel meshes in the bioinspired replica molding process.