Nonfreezable Water and Polymer Swelling Control the Marine Antifouling Performance of Polymers with Limited Hydrophilic Content

Zwitterionic chemical groups have well-documented resistance to marine fouling species when presented as homogeneous polymer brushes. These model formulations are not, however, suitable for practical fouling-control applications. It is presently unknown if a uniform film of zwitterions is required to elicit nonfouling character via the binding of interfacial water or if the incorporation of zwitterionic functionality into a more practical bulk polymer system will suffice. Here, copolymers of n-butyl methacrylate were synthesized with low incorporation levels (up to 20 mol %) of hydrophilic functionality, including zwitterionic moieties. Their antifouling (AF) properties were evaluated using barnacle cyprids (Balanus improvisus), diatom cells (Navicula incerta), and a multispecies biofilm. The laboratory assays revealed higher resistance of ionic copolymers toward cyprid settlement, which was attributed to their swelling and the presence of nonfreezable water molecules bound tightly to the polymer chains. Additionally, cells of N. incerta and the multispecies biofilm were removed more effectively on polymers containing sulfobetaine methacrylate and sulfopropyl methacrylate moieties. The results indicate that the presence of tightly bound interfacial water is not limited to model systems of pure hydrophilic homopolymers, but that this mechanism can also reduce the settlement and adhesion of fouling species via bulk copolymer systems with limited hydrophilic content. The swelling of polymers with hydrophilic content may also contribute to their AF efficacy, and such materials may therefore represent a route to translation of the well-documented nonfouling character of zwitterions into practical, industrially relevant coating formulations.