Interfacial Regulation via Organic-Inorganic Interpenetrating Networks for Enhanced Protection in Waterborne Polyurethane Nanocomposites

The abundance of hydrophilic groups and the linear polymer chain structure in waterborne polyurethane (WPU) lead to insufficient water resistance and corrosion protection. These inherent characteristics make it challenging for WPU to be applied in the marine protection field, where high comprehensive performance of coatings is demanded. Herein, a WPU nanocomposite was designed incorporating hydroxyl-terminated polydimethylsiloxane and bifunctionalized nano-silica (modified with 3-aminopropyltriethoxysilane and propyltrimethoxysilane) during prepolymerization. This strategy established an organic-inorganic interpenetrating cross-linked network through covalent bonding and intermolecular interactions. The silica nanoparticles act as interfacial bridges between polymer segments, mitigating phase separation and agglomeration caused by polarity mismatch, thereby enhancing coating compactness and improving stress transfer. Performance tests demonstrate that the properties of the coating have been comprehensively enhanced. The coating exhibits an elongation at break of 254.64% while maintaining a tensile strength of 21.17 MPa. Additionally, the water absorption rate of the coating decreases to approximately 5%, the electrochemical protection efficiency reaches 99.9920%, and no obvious corrosion phenomenon is observed after a 7 day salt spray corrosion test. Additionally, the coating shows excellent drag-reduction performance, with a drag-reduction rate of 6.56% under turbulent flow. By integrating interfacial design with nanocomposite architecture, this work develops a robust WPU coating system suitable for marine engineering applications, and employs molecular dynamics simulations to reveal the microscopic mechanism by which amino and n-propyl silane dual modification inhibits the aggregation of silica nanoparticles as well as the interfacial interaction mechanism, thereby highlighting the role of colloidal and nanomaterial strategies in advancing functional protective coatings.