What is a coating?
A coating is a covering that is applied to the surface of an object. The purpose of applying the coating may be decorative, functional, or both. Coatings are ubiquitous and can be found on walls, furniture, on all sorts of wires and printed circuits, the outside of houses and cars, and much more. In addition, the decorative duties of coatings span quite a broad spectrum.
Decorative coatings are mainly used for their color, texture or other visual property. Functional coatings are applied to change the surface properties of the substrate, such as adhesion, wettability, corrosion resistance, wear resistance and more. In some cases, the coating adds an entirely new property such as a magnetic response or electrical conductivity and forms an essential part of the finished product.
Coatings may be used in various processes, that are roughly divided into: vapor deposition, spraying, chemical and electrochemical techniques, roll-to-roll coating processes and other, less prominent techniques.
What is graphene?
Graphene is a two dimensional layer of carbon atoms, arranged in the form of a honeycomb lattice. It is touted as a “miracle material” because it is endowed with an abundance of astonishing traits - this thin, one atom thick substance is the lightest, strongest, thinnest material known to man, as well as the best heat and electricity conductor ever discovered - and the list does not end there. Graphene is the subject of relentless research and is thought to be able to revolutionize whole industries, as researchers work on many different kinds of graphene-based materials - each one with unique qualities and purpose.
Graphene for coatings
The vast selection of extraordinary properties that graphene possesses can open the door to many interesting types of coatings, paints, inks and more. Graphene's high resistivity can make for durable coatings that do not crack and are resistant to water and oil; its excellent electrical and thermal conductivity can be used to make various conductive paints, and a strong barrier effect can contribute to extraordinary anti-oxidant, scratch-resistant and anti-UVA coatings.
Graphene enables a wide array of functional coatings and paints, for many possible applications. Among these can be high performance adhesives enabled by graphene's high adhesion property, anti-bacterial coatings, solar paints (capable of absorbing solar energy and transmitting it), paints that provide isolation for houses, anti-rust coatings, anti-fog paints and UV ray blockers, non-stick coatings for various domestic applications (like frying pans and countertops) and even a much-hyped possibility (currently under scientific examination) of a coating that turns a regular wall into a screen.
Commercial activity
Graphene-enhanced products are yet to reach widespread commercialization. Nonetheless, given graphene’s impressive array of properties and the vigorous R&D that is taking place, graphene-enhanced coatings should not be too far away.
The Sixth Element Materials, a Chinese company that focuses on R&D, mass production and sales of graphene and related materials, showcased its graphene-zinc anti-corrosion primer used for offshore wind power tower, that can come at a competitive price compared with zinc rich epoxy primer.
Garmor, the University of Central Florida spin-off formed to develop a new graphene oxide flakes production process, has developed graphene oxide-based coatings useful for limiting UV radiation damage to sensors and polymers. Garmor's transparent GO-films are reportedly derived from a commercially-viable and scalable process that can be readily implemented with minimal constraints.
Four layers of GO coating on polycarbonate
The Spain-based Graphenano announced the launch of a graphene-based series of paints and coatings called Graphenstone in 2014. These are said to be very strong and also acts as a protective layer against environmental damage. Graphenstone is made from a graphene powder and limestone powder.
The British Electro Conductive Products released a sprayable transparent conductive coating based on a CNT and graphene platelets (GNP) hybrid material. TBA are targeting the food, electronics, pharmaceuticals and petrochemicals markets.The new ATEX-compliant product is available as a clear, anti-static aerosol, and it should also be available as bulk paint. Its application will safeguard electronic equipment used in explosive environments and bring it up to European standards.
Further reading
The latest graphene coating news:
MIT team uses wax to smooth out wrinkles in graphene
Researchers at MIT have utilized an everyday material - wax- to protect graphene from performance-impairing wrinkles and contaminants. Removing graphene from the substrate it’s grown on and transferring it to a new substrate is known t be challenging. Traditional methods encase the graphene in a polymer that protects against breakage but also introduces defects and particles onto graphene’s surface. These interrupt electrical flow and stifle performance.
a Schematics showing the process of paraffin-assisted graphene transfer. b Schematics showing the effect of paraffin’s thermal expansion on graphene wrinkle. c A typical paraffin-supported graphene film floated on water at different temperatures
The MIT team describes a fabrication technique that applies a wax coating to a graphene sheet and heats it up. Heat causes the wax to expand, which smooths out the graphene to reduce wrinkles. Moreover, the coating can be washed away without leaving behind much residue.
James Briggs to launch graphene-enhanced hycote range using AGM’s materials
James Briggs has announced the successful completion of its graphene products' first production batch, which is seen as a significant milestone on the path to commercial realization. James Briggs has been working with Applied Graphene Materials on the development of graphene-based anti-corrosive coatings.
Extensive testing has demonstrated repeated and outstanding improvements in anti-corrosion performance for their automotive aerosol primer. JBL plans to launch the new range of graphene enhanced anti-corrosion aerosols under their brand Hycote .
CPI, Haydale and others collaborate on Smart Filter project
The Centre for Process Innovation (CPI) has collaborated on a project to advance the development of a low-cost, self-cleaning coating technology for industrial filter membranes.
The Smart Filter project used graphene and its derivatives to create a coated filter membrane that offers increased resistance to fouling for industrial waste water treatment. Membrane filters are used in a number of industrial separation applications but are afflicted by fouling, which typically lowers throughput or increases energy consumption, and reduces filter life. Focusing upon oil water separation and nuclear waste water treatment, the collaboration, with G2O Water Technologies, Haydale and Sellafield, developed a repeatable, reproducible and scalable process to make coated filter membranes, which delivered a 30% improvement in permeability when compared to an equivalent uncoated filter.
Northwestern team develops graphene-based self-healing coating
Researchers from Northwestern have developed graphene-enhanced self-healing coatings on metal surface based on oil. Jiaxing Huang, professor of Materials Science and Engineering at Northwestern, explains: “the unusual part is that the oil coating does not drip, sticks very well, and at the same time can rapidly heal when scratched. Such coatings can protect metal surface from highly corrosive environments.”
The self-healing material was achieved by modifying an oil with lightweight hollow particles in the form of tiny graphene capsules, measuring just tens of microns in size. These capsules form a network in the oil, preventing the oil film from shrinking or dripping. However, they still allow oils to flow when a scratch breaks the network, thereby healing the damaged area. In a proof of concept demo, the researchers showed that the material is able to heal repeatedly. Even after being scratched in the exact spot for nearly 200 times in a row, it was still able to return to its former un-visibly damaged state within seconds.
University of Manchester researcher develops GO coating that makes living cells and tissues more visible
University of Manchester researcher, Dr Thomas Waigh, has developed a technology that may make living cells and tissues more visible during analysis through the addition of graphene oxide (GO). The use of a GO GO coating to microscopy slides was found to improve both fluorescence imaging contrast and resolution.
Dr Waigh said: “My team has developed technology which uses monomolecular sheets of GO to coat microscopy slides, thereby eliminating background fluorescence and improving the resolution of images”. "It’s an important breakthrough as GO is cheap and easy to manufacture in large quantities. The cost to coat each slide is estimated to be 12 pence".