Amphiphilic/Hydrophilic Polyurea-Enabled Stable and Transparent Bilayer Hydrogel Coatings on Glass for Underwater Optical Antifouling

Abstract Fabrication of underwater stable hydrogel coatings on solid substrates via a facile and scalable method remains challenging. This study presents a simple bilayer hydrogel coating strategy for constructing underwater stable and transparent hydrogel coatings on glass, wherein the amphiphilic polyurea (PU) hydrogel and hydrophilic PU hydrogel serve as the bottom adhesive layer and top antifouling layer, respectively. By incorporating a long aliphatic alkyl chain into the backbone of amphiphilic PU via a special diisocyanate, the amphiphilic PU can assemble into a mechanically robust (tensile strength >1 MPa) and antiswelling (water content ≈ 45%) hydrogel with exceptional underwater adhesiveness. Meanwhile, the hydrophilic PU hydrogel is robust (tensile strength >1.5 MPa), antiswelling (water content ≈60%), and intrinsically superhydrophilic. Benefiting from the synergistic combination of these properties, the bilayer hydrogel coating achieves strong underwater adhesion to the glass substrate, retains high durability to various damaging tests, and maintains a nearly constant underwater–oil (CCl4) contact angle of 148 °. Furthermore, the bilayer hydrogel coating demonstrates outstanding underwater antioil-fouling and antiprotein adsorption (coverage of bovine serum albumin (BSA) <5%) performance, outperforming the single-layer amphiphilic PU hydrogel coating counterpart. This work provides a facile yet effective approach to constructing underwater stable, transparent, and antifouling hydrogel coatings on glass, showing a promising practical application in underwater antifouling of optical devices.