Superhydrophobic Thin Film of Imine-Linked Covalent Organic Networks Obtained via Cascaded Electrochemical Activation and Phase Separation for Water Repellent Surface

The development of superhydrophobic films is critical for various applications but requires materials with enhanced durability and solvent resistance. While covalent organic frameworks (COFs) and covalent organic networks (CONs) offer promising chemical stability and tunability, conventional superhydrophobic films often rely on environmentally harmful perfluoroalkyl modifications. This study introduces an eco-friendly, morphology-tuned CON film fabricated via an ambient electrochemical approach, utilizing an intermediate state on COF formation to induce a sponge-like structure with superhydrophobic properties. The submicrometer-scale porous structure was realized, likely based on the cascaded processes: electrooxidative generation of protons on the electrode, gel-state COF intermediate formation, and phase separation. The resultant low-crystalline CON film showed a superhydrophobic surface, namely, 156.0 ± 2.1° of water contact angle, and enhanced solvent resistance originating from the durable nature of CONs. As an application of the proposed method, a superhydrophobic composite membrane consisting of CON and a metal-mesh support was successfully fabricated through simple electrolysis and exhibited selective water/oil permeability. The CON film with a position-dependent contact angle was realized by using a bipolar electrochemistry technique. The proposed morphology-tuning methodology for CON films has the potential to enable the development of functional films with unique surface properties.