Scalable and Durable Superhydrophobic Coating Using Shellac-Based Bioadhesive and Hierarchical Silica Nanoparticles

Superhydrophobic coatings have broad applications across various fields but often face challenges, such as complexity, high cost, low mechanical/thermal stability, toxicity, and environmental hazards. In this study, we demonstrate a simple, scalable, eco-friendly, and durable spray-coating method using bioadhesive shellac and octadecyltrichlorosilane (OTS)-modified silica nanoparticles to create superhydrophobic surfaces. The silica nanoparticles impart superhydrophobicity by forming hierarchical micro/nanostructures and reducing surface free energy, while shellac ensures strong adhesion of the nanoparticles to a wide range of substrates, including nonwoven polypropylene fibers, glass, plastic, metal, wood, cotton, and concrete. The coating exhibits excellent superhydrophobic performance with a large contact angle (162.1°), a small sliding angle (4°), and low contact angle hysteresis (4°). The coated surface retains its superhydrophobicity even after 50 cycles of sandpaper abrasion, heat exposure up to 150 °C, and contact with acidic environments (pH ∼4.2). These biocompatible and eco-friendly superhydrophobic coatings hold promise for use in applications where safety and environmental protection are critical, such as in antifouling, food packaging, and agricultural/biomedical fields.