Giving graphene a Teflon-like tweak with nanotechnology could soon produce some of the smoothest, sleekest ship hull coatings ever, a team of researchers says.
The team, led by physicist James Dickerson of Vanderbilt University, has developed methods to produce large-area “water-hating” or “water-loving” films of graphene oxide from aqueous suspensions using electrophoretic deposition. The technique combines an electric field within a liquid medium to create nanoparticle films that can be transferred to another surface.
Changing the suspension’s pH and deposition voltage can produce either a porous, rough “brick” microstructure that makes water bead up and run off or a smooth “rug” microstructure that causes water to spread out in a thin layer, the team reports in ACSNano. Either microstructure can be produced as a freestanding film for application to a variety of substrates.
Vanderbilt University / Daniel Dubois
|Graphene films are transparent and inexpensive to make, says James Dickerson.|
Slippery and Cheap
The super-slippery “rug” microstructure could produce a coating that makes ship hulls so slick that they glide through the water more efficiently than ordinary hulls, the researchers report in “Transferable Graphene Oxide Films with Tunable Microstructures.” Or, it may be used to make windshields so slick that they don’t require wipers.
“Graphene films are transparent and, because they are made of carbon, they are very inexpensive to make,” Dickerson said. “The technique that we use can be rapidly scaled up to produce it in commercial quantities.”
|Dickerson can tweak the process for creating films of graphene oxide. The “rug” process creates an extremely smooth, “water loving” film; the “brick” process creates a rough, “water hating” film.|
Graphene has become a hot topic in materials research, including potential applications for coatings. The flake of carbon was the research focus for the 2010 Nobel Prize for Physics. Graphene can conduct heat and electricity as well as copper. It is almost transparent, yet so dense that not even helium can pass through it, experts say.
“Graphene is stronger and stiffer than diamond, yet can be stretched by a quarter of its length, like rubber. Its surface area is the largest known for its weight,” said Andre Geim, one of two Nobel Prize winners recognized in October for their experiments with graphene.
A Wichita State University researcher has already found that graphene, when used as a coating additive, helps protect advanced fiber-reinforced composite wind turbine blades from UV degradation and corrosion from weathering.
Still, Dickerson is one of the first researchers to investigate how graphene interacts with water.
Exploring the Wet Technique
Many scientists studying graphene make it using a dry method, called “mechanical cleavage,” that involves rubbing or scraping graphite against a hard surface. The technique produces sheets that are both extremely thin and extremely fragile. Dickerson’s method can produce sheets just as thin but considerably stronger than those made by other techniques, Vanderbilt says.
The “wet” technique is already used commercially to produce a variety of different coatings and ceramics. Dickerson’s approach could create films that enhance the water-associated properties, making them even more effective at either spreading out water or causing it to bead up and run off.
There is considerable academic and commercial interest in the development of coatings with these enhanced properties, called super-hydrophobic and super-hydrophilic. Potential applications range from self-cleaning glasses and clothes to antifogging surfaces to corrosion protection and snow-load protection on buildings.
However, effective, low-cost and durable coatings have yet to make it out of the laboratory.
Dickerson’s idea is to apply his basic procedure to “fluorographene”—a fluorinated version of graphene that is a two-dimensional version of Teflon—recently produced by Kostya S. Novoselov and Geim for their Nobel Prize-winning research.
Normal fluorographene under tension should be considerably more effective in repelling water than graphene oxide. So there is a good chance a “brick” version and a “rug” version would have extreme water-associated effects, Dickerson figures.
Graduate students Saad Hasan, John Rigueur, Robert Harl and Alex Krejci, postdoctoral research scientist Isabel Gonzalo-Juan and Associate Professor of Chemical and Biomolecular Engineering Bridget R. Rogers contributed to the research, which was funded by a Vanderbilt Discovery grant and by the National Science Foundation.