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

Abstract

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 degrees), a small sliding angle (4 degrees), and low contact angle hysteresis (4 degrees). The coated surface retains its superhydrophobicity even after 50 cycles of sandpaper abrasion, heat exposure up to 150 degrees C, and contact with acidic environments (pH similar to 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.