Alkyl Side-chain Engineering for Enhanced Anti-wettability and Stability in Non-fluorinated Liquid-repellent Coatings

Developing nonfluorinated low-surface-energy coatings with robust environmental adaptability is crucial for green and sustainable industrial applications. Despite substantial advances in hierarchical structures and low-surface-energy chemical design strategies, the specific effect of alkyl chain length bearing a tertiary amine group in nonfluorinated low-surface-energy systems on the dynamic wetting behavior and long-term stability of liquid-repellent coatings remains underexplored. Here, the impact of alkyl side-chain length on the dynamic wettability and stability of superhydrophobic coatings is investigated. Three amine-functionalized monomers with varying alkyl side-chain lengths (C3, C6, and C9) are synthesized and grafted onto nanosilica via polymerization to form organic-inorganic hybrid coatings. The results show that increasing the alkyl side-chain length enhances the dynamic antiwetting capability and droplet bouncing behavior. Notably, the coating with the longest alkyl side chain exhibits an ultralow water adhesion of 22 μN, enabling up to eight successive droplet rebounds upon impact due to the "spring-like" behavior of the extended alkyl chain. Moreover, increasing the alkyl side-chain length significantly enhances the water resistance and UV stability of the coatings. The C9-based coating demonstrates satisfactory durability, withstanding 288 h at a 5 cm depth and 192 h at a 25 cm depth of water, while maintaining stable superhydrophobicity even after 672 h of UV exposure. These findings demonstrate the critical role of alkyl side-chain length in regulating dynamic wettability and stability, providing insights for the rational design of durable fluorine-free superhydrophobic coatings for practical applications.