Underwater Painting Self-Stratifying Zwitterionic Coatings with Integrated Antifouling and Anticorrosion Properties

Marine biofouling and corrosion pose significant challenges to the marine industry. However, conventional coatings generally fail to integrate antibiofouling, anticorrosion, and underwater painting functions, limiting their effectiveness in harsh marine environments. In this study, we fabricated a multifunctional coating comprising bisphenol A epoxy resin, hyperbranched thiol-oligosiloxane (HPSi-SH), and a zwitterionic precursor modified with fluorocarbon chains and epoxy groups. When coated on a substrate, the zwitterionic precursor tends to enrich on the coating surface due to the low surface energy of its fluorocarbon chains, thereby forming a self-stratifying structure. Furthermore, the epoxy groups in the precursor, along with the epoxy resin, cross-link with the HPSi-SH to form high-density three-dimensional networks. After immersion in seawater, the coating surface hydrolyzes and transforms to a hydrophilic zwitterionic layer. This layer prevents the absorption of proteins and the adhesion of bacteria ( Escherichia coli, Staphylococcus aureus, Pseudomonas sp.), diatoms ( Navicula incerta ), and oils. The epoxy–siloxane hybrid matrix maintains strong adhesion to various substrates and exhibits excellent corrosion resistance. In addition, the unique fast-curing and hydrophobicity of the coating before hydrolysis allow for underwater painting. This study presents a strategy for designing multifunctional coatings that combine durability, antibiofouling, and anticorrosion properties for marine applications.