Coating to reduce drag, increase bouyancy

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Researchers from the Nanoprobe Laboratory for Bio- and Nanotechnology and Biomimetics at Ohio State University are developing a biomimetic coating for use on ships and submersible aquatic vehicles. The purpose of their research is to mimic the air trapping ability of the water fern Salvinia molesta, an aquatic plant that traps air on the surface of its leaves. The research team has demonstrated microfabrication techniques that can be applied in various industries. These techniques can be used to produce materials that reduce drag in water by using a layer of air to repel surrounding water.A micropattern with comparable dimensions to the water fern hairs is created in the lab. The micropattern is treated with a hydrophobic (water-repelling) coating that is then stripped away to produce a new microstructure that is hydrophobic everywhere except on its tips. This development process mimics the water fern hairs by exhibiting a hydrophobic base and hydrophilic (water-attracting) tip. While it may seem counterintuitive to have a surface that attracts water while building underwater machinery, it is actually beneficial because it holds the water at a consistent distance from the material's surface. This results in an even surface that does not allow the water to interact with the larger surface area in between the microstructures. This layer of water also locks in air between the microstructures, providing buoyancy for objects in and under the water.

Key Differentiators

Decreasing drag and increasing bouyancy of ships or submarines increases the efficiency of these vessels, reducing the amount of fuel required to power them.

Challenges Solved

"Air-retaining surfaces are of technological interest due to their ability to reduce drag when used for fluid transport, ship coatings and other submersible industrial products in which drag is a concern. Superhydrophobic surfaces have been utilized to obtain the desired air film for the previously stated applications, however the effect called 'giant liquid slip' has been shown to deteriorate the presence of such air films in a matter of minutes. Therefore, S. molesta’s unique ability to pin water and trap air is of importance in order to increase the durability and lifetime of air pocket formation for drag reduction in industrial use" (Hunt and Bushan 2011: 187).

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References


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Nanoscale biomimetics studies of Salvinia molesta for micropattern fabricationJournal of Colloid and Interface ScienceJuly 16, 2011
James Hunt, Bharat Bhushan

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