Tough and Functional Hydrogel Coating by Electrostatic Spraying

Hydrogel coatings impart superior surface properties to materials, but their application on large and complicated substrates is hindered by two challenges: limited wetting conditions and intricate curing processes. To overcome the challenges, lyophilized adhesive hydrogel powders (LAHPs) are developed, which consist of poly(acrylic acid-co-3-(trimethoxysilyl)propyl methacrylate) crosslinked with chitosan. These powders are electrostatic sprayed onto substrates to address wetting issues and rehydrated to form bulk hydrogel coatings to circumvent curing challenges. This approach enables the application of hydrogel coatings with a smooth surface and adjustable thickness on various materials, irrespective of category, geometry, or size. The coatings exhibit remarkable mechanical properties (strength of 2.62 MPa, elastic modulus of 6.84 MPa, and stretchability exceeding 3 folds) and robust adhesion (adhesion energy ≈900 J m^-2) through a three-step bonding process involving electrostatic attraction, hydrogen bonding, and covalent bonding. Notably, these coatings confer multiple functional attributes to the substrate, including lubricity, hydrophilicity, nucleation inhibition, and pH-responsive actuation. Moreover, incorporating LAHPs with functional agents or rehydrating with functional solutions opens possibilities for diverse functional hydrogel coatings, such as thermal responsiveness and NH₃ indication. Leveraging the virtues of simplicity, flexibility, convenience, and broad applicability, this strategy presents an enticing pathway for the widespread applications of hydrogel coatings.