Engineering Fluorine-Free Superhydrophobic Wood via Lignin Nanospheres for Sustainable Surface Protection

Superhydrophobic coatings can effectively enhance the stability and durability of moisture-absorbing materials like wood. Yet, their poor environmental compatibility, weak mechanical durability, and limited functionality hinder further practical use. Herein, a fluorine-free superhydrophobic wood coating was constructed using lignin nanospheres via a simple spray-coating process. The hydrophobic performance of the coating shows a nonmonotonic dependence on the octadecyltrichlorosilane (OTS) amount. Insufficient OTS results in a sparse and adhesive surface, whereas excessive OTS buries the hierarchical structure. Under ideal conditions with a mass-to-volume ratio of 3.3 μL/mg between the OTS and lignin, the coating develops a unique hierarchical structure that demonstrates exceptional superhydrophobicity (contact angle: 163.6° ± 0.5°, rolling angle: 5.3° ± 0.2°) and self-cleaning capabilities. The superhydrophobic coating maintains structural integrity and performance stability under various mechanical damage conditions. Furthermore, the coating exhibits significant photothermal effects, maintaining consistent temperature increases across five heating/cooling cycles, demonstrating excellent thermal stability. Leveraging its superior photothermal conversion capability, the coating enables efficient active deicing and rapid detachment upon substrate inclination. This study provides an innovative approach for the high-value utilization of lignin and the development of green, multifunctional, superhydrophobic coatings.