Patent Application
20150344705
1. Field of the Invention
This invention relates generally to techniques for resisting or preventing the occurrence of biofouling on a surface.
2. Description of the Related Art
There are numerous situations in which a surface needs to be resistant to the growth of various organisms. For example, surfaces immersed in bodies of water, such as the ocean, can become fouled by marine life. Additional examples includes surfaces in a hospital or in a food preparation facility that need to be resistant to the growth of bacteria.
One such situation involves the use of ‘marine streamers’—i.e., long cables that are deployed in the ocean and used for seismic exploration. Typically, streamers (which can be 75 meters long or more) are spooled for transportation to ships, and are unspooled when ready to be used. However, once unspooled into the ocean, streamer cables are susceptible to fouling, especially from barnacles. Very high maintenance costs can be incurred in keeping such cables clean. One way to combat this is to apply a toxic coating such as tributyl tin on the streamer. However, such coatings may be subject to complex regulations.
Another approach is to use a sticky, soft—but non-toxic—coating on the streamer. An example would be the silicone-based coatings currently gaining market acceptance as non-toxic ship hull coatings. However, such coatings can lead to a ‘self stiction’ problem in which sections of the streamer stick to each other when the streamer is spooled, thereby damaging the coating. Another problem is that a very large shear may be needed to dislodge some foulants.
Yet another approach is to use photolithography to create a specific foul-resistant pattern on the surface. However, this can be very expensive, and may be impractical for large surfaces such as a marine streamer.
In a hospital setting, a toxic coating such as silver ion can serve as an anti-microbial coating. This approach may also be subject to strict regulations, and may pose a danger to patients and staff that come into contact with the coated surface.
A method for biofouling mitigation using a surface coating with magnetically aligned particles is presented, which provides a practical, low cost rough surface coating which resists the growth of organisms such as marine life and bacteria.
The present method comprises providing a coating material that requires curing, adding magnetic particles to the coating material, applying the coating material with the magnetic particles to the surface to be coated, subjecting the applied coating to a magnetic field in situ such that the magnetic particles are formed into microstructures that render the surface to be coated rougher than it would be without the microstructures, and allowing the coating to cure. The random and non-toxic surface features created by the magnetic particles and magnetic field provide the coated surface with broad spectrum fouling resistance against organisms such as barnacles and bacteria.
The coating material preferably comprises a fast curing polymer, and the magnetic particles are preferably anisotropic nanoparticles. In practice, the surface to be coated has an associated axis, and the magnetic field is oriented such that it is normal to the axis.
These and other features, aspects, and advantages of the present invention will become better understood with reference to the following drawings, description, and claims.
a and 2b are diagrams illustrating the effect of a smooth surface versus a surface coated as described herein on the ability of a barnacle to attach to the surface.
The present method for biofouling mitigation using a surface coating with magnetically aligned particles is illustrated in
In step 18, the applied coating is subjected to a magnetic field in situ, such that the magnetic particles align and form into microstructures which make the coated surface rougher than it would be without the microstructures. The coating is then allowed to cure (step 20), completing the process.
The present method could be used with any surface on which biofouling might occur. For example, a coating with magnetically aligned particles as described herein could be applied to the surface of a streamer cable used in the ocean, to discourage the attachment of marine life such as barnacles to the cable. This is illustrated in
The present method might also be used to provide a coating to mitigate the fouling of surfaces with bacteria; this can be particularly important in the medical and food industries. For example, with respect to the food industry, the colonization of bacteria on equipment surfaces—which is exacerbated in environments containing food particles—can be very harmful for equipment that comes into contact with food. However, the non-toxic spiky surface produced by the present method reduces biofilm colonization on the surface. Many other applications are possible. For example, common surfaces such as those on optical windows or LCD panels can be adversely affected by biofouling, and thus could benefit from the present method.
The coating material is preferably a polymer matrix, with a fast curing polymer. The curing process is preferably catalyst-based, UV-based or thermal. The coating material is preferably selected from a group consisting of epoxies, silicones, polyurethanes, acrylates, styrene, terephthalates, nylons, polyethylene, polypropylene, and rubbers.
The magnetic particles preferably comprise nanoparticles which have a high magnetic susceptibility. The magnetic particles are preferably based on materials selected from a group consisting of nickel platelets, cobalt, iron, gadolinium, neodymium or samarium, or mixtures thereof. The magnetic particles are preferably anisotropic, with a diameter of 2-3 microns and a thickness of 0.2 microns or less. Needle-shaped particles are preferred.
When a coating as described herein has been applied to the surface, the applied coating is subjected to a magnetic field in situ such that the magnetic particles are formed into microstructures that serve to roughen the coated surface. The surface to be coated typically has an associated primary axis; the magnetic field is preferably oriented such that it is normal to the axis.
This is illustrated in
The concentration of magnetic particles within the coating material affects the base radius and quantity of the resulting microstructures. For example, a concentration of magnetic particles of 1% (by weight) in the coating's polymer matrix will produce microstructures that are sharper (i.e., with a smaller base radius) than a coating with a 2% concentration, but the 1% concentration will produce fewer microstructures than will the 2% concentration.
“Peak sharpness” is one measure of a structure's shape, defined as the height of the structure divided by its base radius. Thus, as discussed above, a microstructure with a smaller base radius will have a greater ‘peak sharpness’. It has been determined that the peak sharpness' of the microstructures formed as described herein have an impact on the effectiveness of the coating in mitigating biofouling. For example, a set of experiments were performed to determine the effect of peak sharpness on the ability of barnacles to settle on a streamer cable. This data is shown in
As noted above, the coating material is allowed to cure after being subjected to a magnetic field in situ. It is preferred that curing occur while the magnetic field is being applied; the microstructures tend to lose sharpness if the coating is allowed to cure in the absence of the magnetic field.
The present method provides a low cost, non-toxic coating that can be applied over surfaces many meters long. The method provides high throughput, and is more commercially feasible than other techniques such as photolithography-based patterning.
The embodiments of the invention described herein are exemplary and numerous modifications, variations and rearrangements can be readily envisioned to achieve substantially equivalent results, all of which are intended to be embraced within the spirit and scope of the invention as defined in the appended claims.
