A gravity-inspired design for robust and photothermal superhydrophobic coating with dual-size lignin micro-nanospheres

The use of renewable materials as structural components for constructing superhydrophobic coatings is an important direction for future development. Here, a robust and photothermal superhydrophobic coating (with a water contact angle of 166.1 +/- 0.8 degrees and a sliding angle of 2.8 +/- 0.1 degrees) is fabricated using dual-size lignin micro-nanospheres (LMNSs), comprising lignin microspheres (m-LMNSs) and nanospheres (n-LMNSs), which successively settle on the substrate surface under the effect of gravity. The microstructure armor formed by the combination of m-LMNSs and epoxy resin endows the coating with excellent abrasion resistance and bonding strength. Moreover, the presence of n-LMNSs within the cavities provides water repellency. The coating maintains superhydrophobicity even after the abrasion distance exceeds 320 cm or after 210 tape peeling cycles. The coating also exhibits robustness under various forms of mechanical and chemical damage. Furthermore, the photothermal effect of the coating enables rapid heating of its surface temperature from similar to 13 to 112 degrees C in only 60 s under laser irradiation. This innovative structural regulation approach enhances the durability and photothermal performance of lignin-based superhydrophobic coatings, demonstrating the practical applicability of the approach.