Graphene Could Change the Future

Author: B. Serhat Cengiz

Technological advances shape the course of history. Iron and steel, for example, played a crucial role in the industrial revolution. Plastics and other petrochemical products are indispensable to every aspect of our lives. Silicon / silicone technologies enabled the electronic revolution. These materials shaped the development of societies, and in the technology race, nations that produced and could effectively use these materials moved ahead of others. Today, a new material called graphene has the potential to change the future.

What is Graphene?

Graphene, in its simplest explanation, is a super-thin layer of graphite. Graphite is not an unfamiliar material to us; we have been using this material, known as pencil lead, since childhood. Graphite is an allotrope of the carbon element, meaning it contains the same atoms, but they are arranged differently. These arrangement differences give the material very different properties. For example, both diamonds and graphite are forms of carbon, but they have extremely different natures. Diamonds are incredibly strong, while graphite is extremely brittle. Graphene was first isolated in 2004 through simple mechanical exfoliation of graphite and attracted great attention due to its unique combination of extraordinary electronic, optical and mechanical properties. Graphene sheets are two-dimensional, single-atom-thick layers of sp2-bonded carbon atoms arranged in a hexagonal, honeycomb-like structure. Interestingly, when graphene is isolated from graphite, it acquires some miraculous properties. It has the distinction of being the first two-dimensional material discovered, despite being only one atom thick. Nevertheless, graphene is also one of the strongest known materials in the universe. With tensile strength of 130 GPa (gigapascals), it is 100 times stronger than steel. Even with graphene being this thin, its incredible strength is already enough to make it remarkable, but its unique properties do not end there. Graphene is also flexible, transparent, highly conductive, and has the property of being impermeable to most gases and liquids. In short, it appears there is no area where graphene is not perfect. In addition to potential applications in advanced batteries and transistors, solar cells, displays, sensors and composites, there is great interest in using graphene as a coating material or as an additive to enhance the performance of various coating technologies. In particular, various approaches are being developed to create corrosion protection coatings based on graphene. In coating technologies, graphene's superhydrophobicity can also provide significant benefits. Additionally, there are many possible applications for conductive graphene coatings.

Brief History of Graphene

Graphite has been a known material for a very long time (used since the Neolithic period). Scientists have pondered whether a single layer of graphite, whose atomic structure was well documented, could be isolated, but until recently, this idea had not been realized. Scientists were uncertain whether it was possible to cut graphite to a single atomic thickness in a single layer. However, in 2004, Andre Geim and Konstantin Novoselov from Manchester University succeeded in obtaining the first isolated graphene sample. Interestingly, the tool they used to accomplish this was remarkably simple—just a roll of tape. When tape was used to polish a large graphite block, these researchers observed extraordinarily thin flakes on the tape. By continuing to peel off layers of graphite flakes, they produced a sample as thin as possible. Eventually, they had found 'graphene'. The discovery was quite strange, and initially the scientific world was skeptical. A respected popular science journal refused to publish the scientists' articles on this subject twice. However, eventually the research was published, and in 2010, Geim and Novoselov were awarded the Nobel Prize in Physics for their discovery.

Potential Markets for Graphene

Graphene coatings can be hydrophobic, conductive, and / or chemically resistant, and therefore are ideal for many applications. Hydrophobic graphene coatings are predicted to be used for water-resistant applications in areas such as ship hulls, products like pots and pans, glass surfaces (mirrors, windows, windshields) and textiles. Conductive graphene coatings will find applications in mobile phones, tablets, computers, television screens and other displays. Graphene coatings can also function as protective coatings with superior chemical, moisture, corrosion, UV and fire resistance properties. In medical devices, these coatings will provide a biocompatible surface that is resistant to degradation. Coating formulators have hitherto adopted inorganic fillers to modify the properties of polymeric coatings. Nanoscale fillers used for decades largely consist of layered clays, carbon nanotubes and their derivatives, and spherical nanoparticles, most commonly silicon dioxide (SiO2). However, most inorganic fillers exhibit poor compatibility with organic polymer resins, and therefore the surfaces of fillers must often be modified to improve filler / matrix interactions. Graphene is attractive as a nanoscale filler because it is a carbon-based material that has better interaction with organic polymers. Therefore, graphene nanosheets and graphene oxide have been investigated as fillers for various coating types. Given the abundance of commercial opportunities in the coating field alone, it is surprising that numerous products have not yet reached the market. The answer is simple—a practical, cost-effective, commercial-scale method for graphene production has not yet been developed. Currently, graphene can only be produced at very high costs and in very small quantities. However, significant advances in production technology are predicted in the future.

Focus on Protective Graphene Coatings

As noted, the scope of research on graphene coatings shows extreme diversity and encompasses both performance properties and potential applications. Many recent studies have focused on developing pure graphene or polymer / graphene composite coatings for protection against corrosion and other damage. Let us briefly examine some of the new findings.

Protection with Pure Graphene

Researchers at Deakin University in Australia showed that graphene flakes grown directly on micron-sized fibers from austenitic stainless steel form a barrier consisting of three-dimensional nanoscale flake networks that provide protection against corrosion. Performance was achieved through enhanced water repellency and graphene's unique electrical properties, which reduce the formation of redox reactions on the surface, with graphene's hydrophobicity. The thickness of the graphene coating was adjusted by varying the temperature during deposition and the feed gas flow rate. Both simple coatings and more complex coatings containing nanopillars of several atomic layers and interconnected 2-4 um length (nanopillars are high-aspect-ratio nanostructures, arranged in large arrays) were synthesized and studied. These final layers exhibited massively developed specific surface areas, superhydrophobicity and the highest corrosion resistance to synthetic seawater. The paper authors believe that the new coating technology can be applied in the development of new heat exchangers, separation systems, adsorption and biocompatible materials. Meanwhile, scientists from the Massachusetts Institute of Technology recently reported that ultra-thin, scalable, chemically vapor-deposited (CVD) graphene coatings have higher chemical resistance than typical functional hydrophobic coatings and promote dropwise condensation rather than film-type condensation on copper condenser tubes used in heat transfer systems. Heat transfer increased fourfold at 100°C in pure steam compared to that of a conventional single-layer hydrophobic polymer coating. The graphene coating was found to be more resistant to chemical attack and provided lower thermal resistance. While the graphene coating showed no signs of measurable degradation over a two-week period, the polymer coating began to degrade within three hours and completely failed within 12 hours. Researchers also calculated, using data from the Electric Power Research Institute, that improved condenser heat transfer could result in a 2-3 percent increase in the efficiency of power plants. Graphene coatings have also been shown to provide greater protection against microbial-induced corrosion compared to typical polymer coatings. Researchers at Rensselaer Polytechnic Institute, South Dakota School of Mines and Technology, Oklahoma State University, and Shenyang National Laboratory of Materials Science determined that graphene coatings protect metallic surfaces from corrosion under harsh microbial conditions better than standard parylene-C (PA) and polyurethane (PU) protective coatings. The results are based on graphene's resistance to microbial attack and the graphene coating being highly suitable and flawless. As a next step, scientists will investigate the performance of graphene coatings on large metal sheets and other metals used in the construction industry under aggressive atmospheric conditions. One of the challenges in developing commercial-scale graphene coatings has been the development of methods for manufacturing large-area, defect-free graphene films suitable for industrial use. Researchers at Manchester University found the solution to this problem by first applying graphene oxide laminates and then chemically reducing them to graphene using hydriodic and ascorbic acids. Through this process, the laminates became highly graphitized with very little structural damage. The films are highly impermeable to gases, liquids and aggressive chemicals, including hydrofluoric acid. Applied Graphene Materials (AGM), a company from the United Kingdom, has developed a scalable production technology uniquely through a continuous synthesis process for a series of graphene nanoplatelets (A-GSMH). To support their focus on developing ready-to-use graphene dispersions for the industry, AGM collaborated with the UK's Paint Research Association to test modified polyurethane and epoxy coatings. Initial results based on small A-GNP10 nanoplatelet additions showed improvements in mechanical properties such as scratch resistance, but notable gains in reducing water vapor transmission rates and anticorosive performance. AGM reported improvements of more than 300 percent from when it failed during cyclic salt spray testing. Researchers at Chung-Yuan Christian University in Taiwan developed electroactive polyimide (EPI) / graphene nanocomposite (EPGN) coatings through thermal imidization and demonstrated that these coatings provided twice the protection against corrosion of cold-rolled steel (CRS) electrodes. Graphene is attractive as a nanoscale filler because it is an advanced carbon-based material and interacts with organic polymers. Corrosion protection is a key issue in the aerospace industry where lightweight is critically important. Graphene coatings have attracted interest because they have the potential to provide corrosion protection even when applied at only a few nanometers thick. Graphene nano fillers are also very attractive because they can significantly improve coating properties at very low loadings. Therefore, researchers at Federico II University of Naples in Italy investigated the effect of graphene nano fillers on the performance of water-based epoxy protective coatings applied to aluminum aircraft alloy Al 2024-T3.6. Graphene technologies can provide performance gains through improved barrier properties and water contact angle without any effect on the hardening process or adhesion properties.

Flexible Electronics

In addition to its strong electrical properties, graphene is also quite flexible and transparent. This makes it attractive for use in portable electronics. Smartphones and tablets could become much more durable with graphene and perhaps even foldable like paper. Wearable electronic devices have recently grown in popularity. With graphene, these devices could become even more useful, designed to flex comfortably around limbs and accommodate various forms of exercise.

Future of Graphene Research

Given these powerful properties of graphene, we would expect to see it everywhere. So why hasn't graphene been widely adopted? As always, the cost factor is decisive here. Graphene is still quite expensive to produce in large quantities, and this limits its use in any product that requires mass production. Additionally, when large graphene layers are produced, there is an increased risk of small cracks and other defects appearing in the material. No matter how incredible a scientific discovery is, economics will always decide its success. Despite all these production challenges, graphene research continues at full speed. Research laboratories around the world—including Manchester University where graphene was first discovered—are continuously filing patents for methods of creating and using graphene. The European Union approved funding in 2013 for a flagship program to finance graphene research for use in electronics. Meanwhile, major technology companies in Asia, including Samsung, are conducting research on graphene technologies. Revolutions do not happen overnight; silicon was discovered in the mid-19th century, but it took nearly a century for silicon semiconductors to lead to the rise of computers. With its almost legendary qualities, could graphene be the force that guides the next chapter in human history, only time will tell.

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