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Research in graphene polymers helps developments in electricals, electronics, medical

 

Graphene polymer thin-film can be used as a replacement for transparent electrical conductors. Flatscreen televisions, computers and mobile phone displays all require transparent electrical conductors to connect embedded electrical devices without obstructing back illumination, as per Nanowerk News. Indium tin oxide (ITO) is currently used for this purpose, but it is expensive and fragile. A low-cost alternative, based on a composite film made of graphene and a ferroelectric polymer, is now available thanks to an international research team, including researchers from the A*STAR Institute of Materials Research and Engineering (IMRE) in Singapore. Graphene is transparent since it consists only of a single layer of carbon atoms. “Graphene can show a high electrical conductivity and is also stronger and much more flexible than indium tin oxide, and thus could even be used for foldable displays and thin solar cells,” explains Guangxin Ni, a PhD candidate in the research team. Very thin, graphene’s single layer of carbon atoms forms strong, tough bonds that explain its good mechanical and electrical properties. In its pristine state, however, graphene’s electrical conductance is low because it has very few free electrons that can carry an electrical current. Injection of electrical charges, usually by applying an electrical voltage, can increase conductivity; however, this is undesirable in consumer devices because it uses electrical power. Ni and his co-workers’ thin film offers a more permanent solution. They combined graphene with a ferroelectric polymer, which has a constant electrical charge on its surface. They grew the graphene on a copper foil by evaporating organic precursor molecules, and then deposited the polymer on top as a thin film from solution. When brought in close contact, the electrical field from the polymer induced electrical charges in graphene. This increased graphene’s electrical conductivity by a factor of 12. The advantage of this approach is that this charge donation is extremely long lasting, indefinitely in theory, and does neither damage to the material nor substantially compromises the high optical transparency of graphene, notes team member Kui Yao from IMRE. Moreover, the fabrication process is very scalable and suitable for industrial applications.

Graphene can kill bacteria and prevent the formation of pathogenic and corrosive microorganisms, which makes it a potential candidate for antimicrobial coatings for surgical equipment and other surfaces in various settings. Graphene can be hard to process on its own because the material tends to clump, but one way to get around this is to mix it with specific polymers. This allows graphene to disperse more readily in solution and coat surfaces more effectively, as per Nanotechweb. Polymer nanocomposites with antimicrobial and biocompatible properties are of growing interest thanks to the variety of applications in areas such as biosensing and biomedical devices. Other uses include water treatment, for example, as membranes for water purification and disinfection. Currently, studies on biomedical, industrial and water-treatment applications of graphene-containing polymer nanocomposites have focused either on the material’s antimicrobial properties or on its human cytotoxity. In order for these graphene-based nanocomposites to be used safely, they need to have both low mammalian toxicity and efficient antimicrobial characteristics. Researchers from the University of Houston and Case Western Reserve University have teamed up to prepare and characterize highly stable graphene (G) poly(N-vinylcarbazole) (PVK) dispersions and films for biomedical and industrial applications, reporting their results in the journal Nanotechnology. The team led by Debora Rodrigues and Rigoberto Advincula prepared highly dispersed PVK-G (97/3 w/w %) nanocomposite solutions in various organic and aqueous solvents by solution mixing and sonication methods, while thin films were fabricated by electrodeposition. The antimicrobial property of the polymer nanocomposite was then tested against Escherichia coli (E. coli) and Bacillus subtilis (B. subtilis). In the study, the scientists found that microbial growth after exposure to the nanocomposite PVK–G presented fewer viable and active bacteria compared with exposure to pure PVK or pure graphene solutions. Furthermore, the PVK–G thin film showed ~80% inhibition of biofilm formation while the PVK and the unmodified surfaces showed almost full coverage (i.e. >80 %). The polymer nanocomposite is highly biocompatible. Overall the team’s results support the potential use of PVK–G for a wide variety of biomedical and industrial applications where bactericidal properties coupled with low cytotoxicity to mammalian cells are vital.

Integrated circuits, which are in everything from coffeemakers to computers and are patterned from perfectly crystalline silicon, are quite thin. Researchers at Cornell University think they can push thin-film boundaries to the single-atom level. Their material of choice is graphene, single atom-thick sheets of repeating carbon atoms, and hexagonal boron nitride, similarly thin sheets of repeating boron and nitrogen atoms. Led by Jiwoong Park, assistant professor of chemistry and chemical biology, the team has invented a way to pattern single atom films of graphene and boron nitride, an insulator, without the use of a silicon substrate. The technique, which they call patterned regrowth, could lead to substrate-free, atomically thin circuits -- so thin, they could float on water or through air, but with tensile strength and top-notch electrical performance. The researchers' patterned regrowth, which harnesses the same basic photolithography technology used in silicon wafer processing, allows graphene and boron nitride to grow in perfectly flat, structurally smooth films, which, if combined with the final, yet to be realized step of introducing a semiconductor material, could lead to the first atomically thin integrated circuit. The research team is working to determine what material would best work with graphene-boron nitride thin films to make up the final semiconducting layer that could turn the films into actual devices.

A team from Rensselaer Polytechnic Institute, New York, have found a way of generating small amounts of electricity by flowing water over surfaces coated with graphene. This energy should be enough to power tiny sensors that are placed in water or other fluids and pumped down into a potential oil well, said research leader Prof Nikhil Koratkar. The graphene coating allows to capture energy from the movement of water over the sensors. The flexible graphene sheets can be wrapped around almost any geometry or shape, it will act as a “smart skin” that serves as a nanofluidic power generator. The water containing the sensors would be injected into the ground and flow through naturally occurring cracks, where the sensors could then detect any hidden pockets of oil and gas. The sensors would remain active as long as water was flowing over the graphene coating, providing enough power to relay collected data and information back to the surface.

 
 
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  Oct 30, 2012
 
 
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