Design and construction of fluorine-free, cost-effective and robust superhydrophobic coatings using nanosilica with highly covalently bonded octadecyl ligands

Abstract

Low surface energy and rough structure are two key factors in achieving superhydrophobicity. Currently, one of the common routes to acquire low surface energy is via the hydrolytic modification of organosilanes. However, due to steric hindrance, self-condensation of hydrolyzed silanes predominates, whereby the resulting products are mainly physically adsorbed or attached to the substrate by few bonds, resulting in the formed superhydrophobic surfaces susceptible to damage by external forces, which significantly inhibits their practical application and long-term service. Herein, we prepared a novel functionalized nanosilica with highly chemically grafted octadecyl ligands in a non-aqueous medium. The covalent bond structure of the product (ODS@SiO2) is approved, and an average grafting density of 10 chains nm−2 was calculated. The ODS@SiO2 has a crystal structure and displays superior thermal and chemical resistance. ODS@SiO2 can be homogeneously dispersed in n-hexane and then applied to various substrates pre-coated with an adhesive by directly spraying or dip-coating to create superhydrophobic coatings. Studies demonstrate that the aggregation of the ODS@SiO2 with high grafting octadecyl ligands on a substrate not only provides a stable low-surface energy layer but also creates multi-level hierarchical structures and microspheres, thus strengthening the robustness of the coating. The coatings exhibit excellent water repellency and self-cleaning ability while maintaining superhydrophobicity after multiple cycles of mechanical abrasion and exposure to harsh environmental conditions. We convince that the fluorine-free, cost-effective and robust superhydrophobic coating has potential applications in various fields.