NANOSCALE GRAPHENE PLATELETS TAKING ITS PLACE AS AN EMERGING CLASS OF NANOMATERIALS

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1 NANOSCALE GRAPHENE PLATELETS TAKING ITS PLACE AS AN EMERGING CLASS OF NANOMATERIALS Ron Beech, Ian Fuller Angstron Materials, Inc. ** Abstract Graphene is no longer just a topic for physicists and chemists to discuss at conferences. The material is making the transition from research journals to commercial applications. The speed of this transition is driven by its unique properties and the ability of manufactures to provide materials in industrial volumes. This article also discusses a new class of nanomaterial now commonly referred to as nano graphene platelets and their commercialization in wide ranging applications. ** Angstron Materials, Inc. is an Ohio-based company that has developed a cost-effective, high- performance, nano-scale material called nano-graphene platelets (NGPs). Angstron is the first company to isolate single-layer and multi-layer graphene structures and successfully produce nano graphene sheets in large quantities. Angstron s nano-graphene materials and several applications are protected by over 150 US patents and several international patents (issued and pending). These patents cover various material compositions and processes for NGPs, NGP nanocomposites, and NGP-based devices. For additional information, please visit contact Ian Fuller at ian.fuller@angstronmaterials.com, or call us at (937)

1. Introduction Graphene s popularity with researchers has risen dramatically. In 2000, the number of scientific papers that included graphene as a topic was less than 100.

2 1. Introduction Graphene s popularity with researchers has risen dramatically. In 2000, the number of scientific papers that included graphene as a topic was less than That number has skyrocketed to more than 9,000 scholarly articles in Further sparking worldwide interests in using graphene in commercial applications was the awarding of the 2010 Nobel Prize in Physics to Andre Geim and Konstantin Novoselov "for groundbreaking experiments regarding the twodimensional material graphene.. 3 Graphene is particularly commercially valuable because it has exceptional electrical, mechanical, thermal, optical, and barrier properties suited to applications in a broad range of industries ranging from aerospace, automotive, composites, energy, marine and electronics to construction, biomedical and telecommunications. 4 In the last decade, fundamental research has prompted corporations to work with graphene manufactures to provide practical modifications to existing products and create new products capable of capturing the performance advantages of this material. 2. The Basics of Graphene Ideal graphene is a composed of a single atom thick sheet of carbon atoms. Well-known forms of carbon include graphite and diamond. Graphene s properties are the result of carbon atoms occupying a two-dimensional hexagonal lattice. These carbon atoms are bonded together through strong covalent bonds at an atomic level and resemble a chicken wire lattice. While there are many potential commercial applications for the graphene materials, some of the key properties useful in real-world applications are illustrated in Figure 1. Figure 1. Key properties of graphene materials that will enable widespread commercialization. 3. Comparing Graphene to Other Nanomaterials Both carbon nanotubes (CNT) and carbon nanofiber (CNF) are effective materials for many exciting applications. CNTs and graphene share similarities including low density, a low percolation threshold for electrical conduction, and high purity. However, as recently demonstrated by Mohammad Rafiee and colleagues, graphene outperforms CNT when measuring mechanical properties in an epoxy. 5 These properties included Young s modulus, ultimate tensile strength, fracture toughness, fractured energy, and the resistance to fatigue crack propagation. 6 Rafiee et al. concluded that the high 2

3 specific surface area, enhanced matrix adhesion arising from the wrinkled surface of graphene and the two dimensional geometry of the material contributed to the results. 7 Beyond the science of graphene is the practical ability of manufacturers to process a nonmaterial into a manufactured product. Unlike graphene, CNTs are long and thin and can easily entangle with one another to form a birds nest structure in applications. As a result, the loading of these nano-fillers dramatically increases the viscosity of a matrix. In contrast, graphene is a two-dimensional platelet that has the capability to slide over one another, allowing for higher loading and lower viscosities. In some applications, the properties of both CNT and graphene are optimized by combining both materials. The graphene acts as a lubricant and bridge between the CNTs and the matrix. Angstron Materials s chief technical officer, Dr. Aruna Zhamu noted that manufacturers familiar with CNTs have found the transition to graphene to be straightforward. 4. History of Graphene Graphene is a relatively new material. In the 1930 s, physicists believed that a two-dimensional plane was not stable enough to exist independently. 8 Microscopy observation of atomically thin graphitic fragments (possibly even monolayers of graphite oxide) was cited as early as with graphitic epitaxial growth reported in Dr. R. S. Ruoff and his research group reported thin sections of highly ordered pyrolytic graphite plates (HOPG) and promised that future work would include trying to obtain single-layer graphene. 11 To understand the full history of graphene, understanding activities surrounding the material outside the scientific literature is essential. Dr. Bor Z. Jang, co-founder of Angstron Materials, Inc., isolated single-layer and multi-layer graphene structures from partially graphitized polymeric carbons. This new class of nano material is now commonly referred to as nano graphene platelets (NGP). In 2002, Jang submitted the world s first patent application on single-layer graphene 12, which was also the first patent for graphene reinforced metal-, glass-, carbon-, and ceramic-matrix composites and single layer graphene-reinforced polymer composites. In October 2004, Andre Geim and Kostya Novoselov, both at Manchester University, published a paper in Science that led to them being awarded a Nobel Prize in Geim and Novoselov isolated graphene using Scotch tape and observed the significant electron mobility of the carbon lattice. 14 Since 2004, Geim and Novoselov, along with thousands of other researchers, have helped unravel the mysteries of graphene and its uses in thermal, electrical, structural, energy, and barrier applications. Furthermore, researchers with corporations around the world have filed hundreds of patents and are seeking to commercialize graphene-enhanced products. 5. Methods for Making Graphene In 2004, Geim and Novoselov obtained graphene by using tape to repeatedly peel off graphene sheets from graphite crystals. 15 Researchers, however, have also used other methods. Researchers have also explored epitaxial growth on silicon carbide by heating silicon carbide (SiC) to high temperatures to reduce it to graphene. Additionally, researchers have grown graphene from metal-carbon melts through a process that dissolves carbon atoms inside a transition metal melt allowing the dissolved carbon to precipitate out at lower temperatures as single layer graphene. Researchers have also produced gram quantities of graphene by the reduction of ethanol by sodium metal followed by pyrolysis of the ethoxide product and washing with water to remove sodium salts. While these methods do produce graphene, they are also expensive and are not practical for large scale production. Jang and his team focused on the properties of graphite and found it was less expensive to take natural graphite and peel it off billion of layers at a time. By physically inserting chemicals such as nitric acid in between layers of graphite you can peel away countless layers, says Jang. The exfoliation process is an economically viable approach that results in graphene being available in large quantities and at competitive prices. Since its founding, Angstron has worked to scale-up the production process of the raw materials and has recently achieved a production capacity of approximately 300 metric tons per year. 3

Graphene is also now available to manufacturers in a variety of forms, including powders, nano-intermediates (solvent dispersions, epoxy dispersions and polymer masterbatches), and enhanced

Applications As scientists consider graphene for future applications such as replacing silicon chips, the material continues to make inroads into applications that have shorter development cycles.

graphene was used to enhance electromechanical properties.

4 Graphene is also now available to manufacturers in a variety of forms, including powders, nano-intermediates (solvent dispersions, epoxy dispersions and polymer masterbatches), and enhanced nanocomposites. Platelets can also be mixed with other nano materials, such as CNFs, CNTs, and nano clay platelets, to produce hybrid materials to achieved tailored material properties. 6. Applications As scientists consider graphene for future applications such as replacing silicon chips, the material continues to make inroads into applications that have shorter development cycles. One of Angstron s customers, for example, introduced the world s first commercial graphene application for actuator and sensing components wherein. graphene was used to enhance electromechanical properties. Angstron is actively partnered with companies in other polymer, coatings, aerospace, electronics, and energy industries to develop applications for lithium ion batteries, supercapacitors, thermal management, inks, EMI shielding, nanocomposites, and more. One of the key applications for graphene is the enhancement of polymer materials, including thermosets, thermoplastics, and elastomers. Melt and solution processing techniques typically used for plastics such as injection molding and extrusion can be used to process graphene-polymer composites. Angstron is working with several partners to develop graphene enhanced nanocomposites and masterbatch materials for a wide range of applications. The formulation possibilities allow for significant property customization for the end user. By selecting specific types of graphene materials and other additives, the nanocomposite can provide enhanced thermal and electrical conductivity, mechanical strength, and barrier properties. Graphene enhanced polypropylene nanocomposite from Angstron Materials. Graphene based thermal spreader dissipating heat. Another of Angstron s key focuses lies in utilizing the thermal conductivity of its graphene materials for thermal management applications. Working with its customers and partners, Angstron has developed a range of technologies and products that have been incorporated into electronics. Angstron s flexible thermal spreader can effectively dissipate the generated heat generated by hand held electronic devices, with a best-in-class in plane thermal conductivity of 1,700 W/m- K. Using graphene materials for thermal management applications affords device designers with weight and volume reduction opportunities. Graphene is especially well suited for energy storage applications such as lithium ion (Li-ion) batteries, supercapacitors, and fuel cells areas of significant international interest. Graphene provides a very high specific surface area up to 2,675 square meters per gram, and inherent electrical conductivity. With competing technologies, researchers have difficulty improving battery performance because of the inability to maintain conductive networks within the electrode during repeated charge-discharge cycles. With limited success, researchers have pursued the approach of mixing silicon (Si) nano particles with carbon to solve this problem for over a decade. Jang et al. have managed to overcome this long-standing technical challenge through using graphene s 2-D geometry and high electrical conductivity. 16 Angstron, and sister company Nanotek Instruments, mixes their NGPs with silicon resulting in an innovative NGP-Si composite that exhibits exceptional energy density while maintaining its structural integrity through hundreds of charge-discharge cycles. 7. Conclusion There are two sides to the story of graphene. Academics are spending millions of hours producing fundamental research on the material. Corporations, on the other hand, are working to create commercial applications that will provide a competitive advantage. The bridge that brings the two sides together has two pillars. Manufactures must provide materials at a reasonable cost (relative to competing materials), high quality, and volume. In addition, their technical sales and research and development staff must monitor the latest findings and provide guidance on the selection, dispersion and 4

5 functionalization of graphene. Angstron Materials is at the forefront of this effort, working to bring graphene materials and products from lab-scale success to commercial reality. 1 The authors used the Web of Science on line database to perform a topic search using the key word graphene. 2 See Andrew Plume, Graphene: ten years of the gold rush, 38 Research Trends (2014). 3 Press Release, The Royal Swedish Academy of Sciences, Awarding of Nobel Prize (Oct. 5, 2010), available at 4 See e.g., Mitra Yoonessi & James R. Gaier, Highly Conductive Multifunctional Graphene Polycarbonate Nanocomposites, 4 ACS NANO 7211 (2010) (discussing electrical properties); Andrey K. Geim & Allan H. MacDonald, Graphene: Exploring Carbon Flatland, 60 PHYSICS TODAY 35 (2007); Xiaoming Sun et al., Nano-Graphene Oxide for Cellular Imaging and Drug Delivery, 1 Nano Res. 203 (2008), available at 5 See Rafiee, supra note 9. 6 See id. 7 See id. 8 See R.E. PEIERLS, HELV. PHYS. ACTA 7 Suppl I1 81 (1935). 9 See e.g., Hanns-Peter Boehm Boehm et al., Das Adsorptionsverhalten sehr dünner Kohlenstoffolien, 316 Zeitschrift für anorganische und allgemeine Chemie 119 (1962). 10 See A.J. van Bommel, J.E. Crombeen & A. van Tooren, LEED and Augerelectron Observations of the SIC(0001) Surface, 48 SURFACE SCI. 463 (1975). 11 Xuekun Lu et al., Tailoring Graphite with the Goal of Achieving Single Sheets, 10 NANOTECH. 269 (1999). 12 US Patent , Process for nano-scaled graphene platelets. 13 See Press Release, supra note See Kostya Novoselov et al., Electric Field Effect in Atomically Thin Carbon Films, 306 SCI. 666 (2004). 15 See id. 16 See e.g., US Patents , , , , , , , , , , , , , , , , , , , , , , , , , , , ,

Commercial Graphene Applications: Current Research and Future Prospects

Commercial Graphene Applications: Current Research and Future Prospects Overview History and Overview of Graphene Angstron Materials and Nanotek Instruments Applications of Graphene Thermal Management