Biomimetic antifouling coating
A biomimetic antifouling coating is a treatment that prevents the accumulation of marine organisms on a surface. Typical antifouling coatings are not
Biomimetic antifouling coatings are highly lucrative because of their low environmental impact and demonstrated success. Some properties of a biomimetic antifouling coating can be predicted from the contact angles obtained from the Wenzel equation, and the calculated ERI. Natural materials such as shark skin continue to provide inspiration for scientists to improve the coatings currently on the market.
Chemical methods
Most antifouling coatings are based upon chemical compounds that inhibit fouling. When incorporated into marine coatings, these biocides leach into the immediate surroundings and minimize fouling. The classic synthetic antifouling agent is tributyltin (TBT). Natural biocides typically show lower environmental impact but variable effectiveness.
Natural biocides are found in a variety of sources, including
Various
A significant drawback to biomimetic chemical agents is their modest service life. Since the natural biocides must leach out of the coating to be effective, the rate of leaching is a key parameter.[8]
Where La is the fraction of the biocide actually released (typically around 0.7), a is the weight fraction of the active ingredient in the biocide, DFT is the dry film thickness, Wa is the concentration of the natural biocide in the wet paint, SPG is the specific gravity of the wet paint, and SVR is the percentage of dry paint to wet paint by volume.
Shark skin mimetics
One class of biomimetic antifouling coatings is inspired by the surface of shark skin, which consists of nanoscale overlapping
Where r is the Wenzel roughness ratio, n is the number of distinct surface features in the design of the surface, and φ is the area fraction of the tops of the distinct surface features. A completely smooth surface would have an ERI = 0.
Using this equation, the amount of microfouling spores per mm2 can be modeled. Similar to actual shark skin, the patterned nature of Sharklet AF shows microstructural differences in three dimensions with a corresponding ERI of 9.5. This three-dimensional patterned difference imparts a 77% reduction in microfouling settlement.[10] Other artificial nonpatterned nanoscale rough surfaces such as 2-μm-diameter circular pillars (ERI = 5.0) or 2-μm-wide ridges (ERI = 6.1) reduce fouling settlement by 36% and 31%, respectively, while a more patterned surface composed of 2-μm-diameter circular pillars and 10-μm equilateral triangles (ERI = 8.7) reduces spore settlement by 58%.[10] The contact angles obtained for hydrophobic surfaces are directly related to surface roughnesses by the Wenzel equation.[11]
See also
- Biofouling
- Fouling
- Anti-fouling
- Biomimicry
- Bionics
- Tributyltin (TBT)
- Sharklet