Contact Angle Analysis, Surface Dynamics, and Biofouling Characteristics of Cross-Linkable, Random Perfluoropolyether-Based Graft Terpolymers

Abstract

The conventional approach to prevention of marine biofouling has been the use of antifouling paints and coatings which function through the release of toxins in the immediate vicinity of the ship. Such technology, while admittedly effective, has proven to be responsible for an alarming increase in the levels of organotin and other toxic materials in and around dry docks, harbors, and shipping lanes which experience significant commercial and tourist traffic. Therefore, our objective is the rational design of minimally adhesive, mechanically stable, nontoxic fouling release coatings as responsible and practical alternatives to antifouling technologies. Herein we report on the synthesis and characterization of a series of cross-linkable perfluoropolyether (PFPE) graft terpolymers containing various alkyl (meth)acrylate monomers with glycidal methacrylate as the cure-site monomer. These materials were targeted for use as coatings to prevent marine biofouling. A series of terpolymers were prepared through application of the macromonomer approach, allowing for control of cross-link density, Tg, and modulus. Structure/property relationships were established through compositional variation with regard to the three classes of monomers. The first monomer class was an alkyl (meth)acrylate used to create the continuous phase of the microphase-separated graft terpolymers. Variation between methyl methacrylate (MMA) and n-butyl acrylate (BA) provided materials with a low (−10 °C) and a high (95 °C) Tg for the continuous phase. This was a means of isolating the effect of modulus and Tg on surface properties, while the basic chemical nature of the monomer remained unchanged. The second monomer class contained a curable functional group. Through incorporation of glycidyl methacrylate (GMA) in the monomer feed and manipulation of curing conditions, the relative effect of cross-link density on surface dynamics has been evaluated. The third monomer class was the PFPE macromonomer itself. The incorporation of this macromonomer was used to enhance the release properties of the resulting materials which relied on surface enrichment of the low surface energy PFPE component. Dynamic surface properties of these materials have been evaluated through dynamic surface tensiometry (DST). Herein, it has been demonstrated that contact angle hystersis can be significantly mitigated (i.e., θr is maximized) by as much as 50° through variation in bulk polymer composition, the chemical nature of monomers, cross-link density, modulus, and environmental conditions at the time of cure. The antifouling and fouling-release potential of the experimental coatings were also evaluated by laboratory assays employing the green fouling macroalga Ulva. The results from these initial studies suggest promising antifouling properties, especially with regard to spore settlement which was strongly inhibited on the experimental surfaces. Additionally, those that did settle were only weakly attached with one sample set exhibiting fairly moderate release of the young Ulva plants.