Environmentally Benign Sol–Gel Antifouling and Foul-Releasing Coatings

• Published in: Accounts of chemical research 2014-02, Vol.47 (2), p.678-687
• Main Authors: Detty, Michael R, Ciriminna, Rosaria, Bright, Frank V, Pagliaro, Mario
• Format: Article
• Language: English
• Subjects: Animals; Bacteria; Bacterial corrosion; Biofouling; Disinfectants - chemistry; Disinfectants - pharmacology; Drag; Gels - chemistry; Gels - pharmacology; Nanotechnology - methods; Paint; Paints; Protective coatings; Ships; Silicon Dioxide; Water temperature
• ISSN: 0001-4842; 1520-4898
• DOI: 10.1021/ar400240n

Biofouling on ships and boats, characterized by aquatic bacteria and small organisms attaching to the hull, is an important global issue, since over 80000 tons of antifouling paint is used annually. This biofilm, which can form in as little as 48 hours depending on water temperature, increases drag on watercraft, which greatly reduces their fuel efficiency. In addition, biofouling can lead to microbially induced corrosion (MIC) due to H2S formed by the bacteria, especially sulfate-reducing bacteria. When the International Maritime Organization (IMO) international convention banned the use of effective but environmentally damaging coatings containing tributyl tin in 2008, the development of clean and effective antifouling systems became more important than ever. New nonbiocidal coatings are now in high demand. Scientists have developed new polymers, materials, and biocides, including new elastomeric coatings that they have obtained by improving the original silicone (polydimethylsiloxane) formulation patented in 1975. However, the high cost of silicones, especially of fluoropolymer-modified silicones, has generally prevented their large-scale diffusion. In 2009, traditional antifouling coatings using cuprous oxide formulated in copolymer paints still represented 95% of the global market volume of anti-fouling paints. The sol–gel nanochemistry approach to functional materials has emerged as an attractive candidate for creating low fouling surfaces due to the unique structure and properties of silica-based coatings and of hybrid inorganic–organic silicas in particular. Sol–gel formulations easily bind to all types of surfaces, such as steel, fiberglass, aluminum, and wood. In addition, they can cure at room temperature and form thin glassy coatings that are markedly different from thick silicone elastomeric foul-releasing coatings. Good to excellent performance against biofouling, low cure temperatures, enhanced and prolonged chemical and physical stability, ease of application, and the waterborne nature of sol–gel coatings all support the diffusion of these paints to efficiently reduce the accumulation of fouling layers on valued surfaces immersed in marine or fluvial waters. Furthermore, sol–gel glassy coatings are transparent and can be effectively applied to optical devices, windows, and solar panels used in lake, fluvial, or marine environments. Sol–gel technology is eminently versatile, and the first generation sol–gel paints have already shown good per