RT&L FOCUS AREA(S): Autonomy;General Warfighting Requirements (GWR) TECHNOLOGY AREA(S): Ground / Sea Vehicles;Materials / Processes OBJECTIVE: Develop marine coatings that deter the settlement of biofouling without relying on the release of toxic chemicals. The coatings must not rely on an external source for activation (i.e., mechanical, optical, chemical) and must be practical for application on the large surface areas of the wetted ship hull. DESCRIPTION: Marine antifouling coatings use biocides to minimize biofouling on ship hulls and are thus a compromise in terms of being environmentally beneficial (e.g., maximizing fuel efficiency, minimizing introduction of non-indigenous species) and environmentally harmful (i.e., releasing toxins). Current coatings either have an ablative matrix that the biocides diffuse through or are self-polishing and slowly hydrolize to release the biocides. When the biocide release rate drops below a threshold, hard foulers such as barnacles can strongly adhere to the ship hull. Alternative "fouling release" coatings have been developed, which do not release biocides and operate as easy to clean coatings which may self-clean by the shear of water against the hull when moving or be easily cleaned with soft brushes or wiping with a sponge. These coatings are generally based on silicone resins sometimes enhanced to present hydrophilic or amphiphilic domains on the immersed coatings surface. However, when ships are idle in port, biofouling can quickly accumulate to the extent that it will not self-clean. This is problematic for the Navy so most ships use antifouling coatings. Commercial marine coatings manufacturers have started to develop hybrid coatings in which biocides are added to fouling release matrices. In some ways, these represent the best of both worlds, but it is doubtful that these coatings will retain these biocides to provide a long coating lifetime. Also, in the long run, non-toxic approaches are desired. The goal of this SBIR topic is to develop environmentally benign coatings that deter settlement without the release of biocides, are effective for five years or more, and are easy to clean should some biofouling occur. To compete with antifouling coatings from a cost/performance perspective, such approaches should not resort to expensive active mechanisms involving electrical, thermal, mechanical, or optical stimulation. There are several approaches to achieve this in the literature, though currently none are fully successful so more development is necessary. The challenge is that the breadth and diversity of the marine biofouling community is high and extends from microscopic to macroscopic (i.e., bacterial to algae and barnacles), though stopping the initial foulers is a good approach. One strategy is to tether the biocides to the coating surface. Efficacy in this approach may depend on the inhibition mechanism of the biocide, and also whether cell debris is easily dislodged enabling the biocide to remain effective [Ref 1]. Another approach involves creating hydrophilic or amphiphilic surfaces using zwitterions. In general, this approach results in easy release surfaces but some methods of presenting the zwitterions seem to make the surfaces deterrent [Ref 2]. Though it is less desirable to release chemicals, registered irritant compounds such as Selektope which could provide a non-toxic coating. Researchers have also investigated release of various biofoulant signaling compounds [Ref 3]. Other novel approaches are welcome. PHASE I: Develop approaches to producing coatings that are easy release and deter biofouling settlement relative to control surfaces (e.g., glass, polydimethylsiloxane (PDMS), commercial fouling release coating (Navy can identify relevant coatings) without releasing toxic compounds. Demonstrate this capability in lab assays against marine fouling on various fouling levels including marine bacteria, algae, and possibly invertebrates such as barnacles or tubeworms. Performers can use their own lab assays and/or submit samples to the ONR basic research program in this area [Ref 4]. Performers that use their own assays will need to calibrate them against the ONR assays. (ONR assays are generally carried out on coated microscope slides and coverslips.) PHASE II: Scale coating for testing of coated 4 inch by 8 inch substrates in static field assays at ONR funded facilities. Optimize coating based on iterations of lab assay characterization and field testing. Optimize coating for longer term performance. Provide a business plan to commercialize coating. PHASE III DUAL USE APPLICATIONS: Scale coating for patch testing on a Navy ship. Execute commercialization strategy for commercial and defense applications. The Navy currently utilizes coatings developed for commercial shipping which pass additional Navy qualification tests. REFERENCES: 1. Park, Daewon; Finlay, John A.; Ward, Weinman, Craig J.; Krishnan, Sitaraman; Paik, Marvin; Sohn, Karen E.; Callow, Maureen E.; Callow, James A.; Angert, Esther R.; Kramer, Edward J. and Ober, Christopher K. Antimicrobial Behavior of Semifluorinated-Quaternized Triblock Copolymers against Airborne and Marine Microorganisms. Applied Materials and Interfaces, 2(3), 210, pp. 703-711. 2. Aldred, Nick; Li, Guozhu; Gao, Ye; Clare, Anthony S. and Jiang, Shaoyi. Modulation of barnacle (Balanusamphitrite Darwin) cyprid settlement behavior by sulfobetaine and carboxybetaine methacrylate polymer coatings. Biofouling, 26:6, 2010, pp. 673-683. 3. Gohad, N.V.; Shah, N.M.; Metters, A.T.; and Mount, A.S. Noradrenaline deters marine invertebrate biofouling when covalently bound in polymeric coatings. Journal of Experimental Marine Biology and Ecology, Volume 394, Issues 1-2, 30 October 2010, pp. 63-73. 4. Stafslien, Shane J.; Sommer, Stacy; Webster, Dean C.; Bodkhe, Rajan; Pieper, Robert; Daniels, Justin; Vander Wal, Lyndsi; Callow, Maureen C.; Callow, James A.; Ralston, Emily; Swain, Geoff; Brewer, Lenora; Wendt, Dean; Dickinson, Gary H.; Lim, Chin-Sing; and Teo, Serena Lay-Ming. Comparison of laboratory and field testing performance evaluations of siloxane-polyurethane fouling-release marine coatings. Biofouling, 32:8, 2016, pp. 949-968.
