Journal of Current Engineering and Allied Science
Volume: 1(1), October 2018, Pages: 13-18
Present Status and Future prospects of Multifunctional Graphene
Received 15Aug 2018; accepted 16 Sep 2018
Available online 3 Oct 2018
Graphene is the name given to a single layer of carbon atoms in a closely packed honeycomb two-dimensional (2D) lattice, which is a basic building block for all other graphitic materials of various dimensionalities. An overview of graphene from its history, properties, and preparation to its application is briefly stated in this chapter. Graphene, since its discovery in 2004, has raised worldwide research interest. The synthesis of high-quality and large-scale graphene nanosheets has been developing well and there have been remarkable outcomes regarding applications of graphene nanosheets in energy storage devices, especially super capacitors and lithium-ion batteries. Graphene represents a promising low-cost carbon material for a broad range of practical applications and its potential in electronics will be further developed in the near future.
Graphene, Carbon, Applications, Engineering
The emerging world of nanotechnology which comes in the wake of major changes in the use of technology, essentially depended on basic materials, has been very slow in the Stone age but picked up a little in the Bronze and Iron ages. In contrast the changes gained momentum from the Chemical age around AD 1900 (Adán-Más et al., 2013; Tang et al., 2013).
Right from the middle ages, the urge to probe matter and manipulate it in search of the proverbial gold has been punctuated by philosophical contemplation on the nature of matter and its constituents. Some of the theoretical predictions have been eventually verified with the advent of modern instruments. The ongoing Information age is noted for outstanding advances in the biological science as well. Biologists and information scientists have joined hands in exploring matter at the nano scale and have discovered new features of many materials. An interdisciplinary study with revolutionary implications for the entire world is emerging. The study of nanotechnology and its applications is expected to dominate the 21st century (Yan et al., 2014; Xie et al., 2013; Chae et al., 2014). Hailed as the all-embracing innovation of the 21st century, nanotechnology is expected to impact on almost all aspects of life. Nanotechnology is an enabling technology, as it would impact on almost every area of research (Zhou et al., 2014; Oh et al., 2014; Dahal et al., 2014; Fen et al., 2015).
Research at the nano scale is bringing together chemists, physicists, chemical engineers as well as computer experts, biologists and doctors in a truly interdisciplinary manner. The results of this endeavour are likely to affect almost every aspect of our daily life. The impact is expected to be global transport, communications, drugs, disease detection and rediscover our immune system, our genetic make-up, reinvent and reengineer industrial production and rewrite the strategy of war. Nanotechnology is designed to bring out an entirely new generation of products, cleaner, stronger, lighter and environment friendly. On the down side, nanotechnology has become a deadly weapon in the hands of terrorists. Even otherwise, the nano revolution could spell the end of human control over matter.
In the last two decades path-breaking discoveries and inventions of new microscopes have led to a lot of hype in the media about the ability of nanotechnology. An overview that separates the science from the fiction in this matter is urgently called for. Moreover, knowledge of the challenges met and the results achieved is essential, if the younger generation in developing countries, such as India were to acquire an interest in the new field of nanotechnology and become motivated to address the challenge of applying it for the benefit of their people. India has taken the initiative to encourage research and application of nanotechnology and selected scientific establishments in the country have done outstanding work on this field (Ghuge et al., 2017) . Conductive polymer nanocomposites, a polymeric material can be made electrically conductive by randomly dispersing an electrically conductive filler phase . The filler size, shape and amount of filler material influence the observed electrical properties of the macroscopic composite. Generally, it is advantageous to have a filler particle with a small size, a high aspect ratio shape and in sufficient quantity; such a combination provides the maximum electrical conductivity .Nanomaterials such as graphene are ideally suited for imparting electrical conductivity in composite materials (Allen et al., 2010).
Figure 1. The honeycomb lattice of graphene. The unit cell defined by vectors a1 and a2 containing the two atoms belonging to sublattices A (blue) and B (red) is highlighted in light blue.
2. Graphene based nanocomposite and its electrical properties
Carbon is an extremely versatile element, not only in the form of organic compounds, but also in inorganic (nano) materials. The two well-known allotropes of crystalline carbon, graphite with sp2 hybridization (black, good electric conductor, soft), diamond with sp3 hybridization (transparent, insulator, hard) and photonic nature have very different physical properties . The large variety of sp2 nanocarbons while others are still hypothetical—obtained by various ways of stacking graphitic elements and/or by incorporating defects in the graphitic network have an even wider range of physical properties depending on their particular structure or, in other words, on the way their constituting atoms are linked together (Khan et al., 2014) .
Why each carbon atom has three nearest neighbors within the graphene sheets. Each pz orbital overlaps with those of the neighboring carbon atoms to form p-bonds that lead to delocalized electron p bands, much like in the case of benzene, naphthalene, anthracene and other aromatic molecules. In this regard, graphene can be thought of as the extreme size limit of planar aromatic molecules. The covalent s bonds (shorter than the C–C bonds in diamond) are largely responsible for the mechanical strength of graphene and other sp2 carbon allotropes. The occupied s electronic bands are completely filled and have a large separation in energy from the Fermi level. For that reason, their effects on the electronic properties of graphene can be neglected, at least to a first approximation (Khan et al., 2014).
At this level of approximation, the band structure—and therefore the electronic properties—of graphene can be addressed by describing the p bands in a tight binding approximation. Band structure calculations for the honeycomb lattice yield an unusual electronic structure: the conduction p band and the valence p band of graphene meet exactly at the corners of the hexagonal first Brillouin zone (Fig.1) and only there. These corners are called the Dirac points. Because of this, graphene is called a zero band-gap semiconductor or semimetal. Around the Dirac points, the dispersion relation of the p-- bands is linear with the separation distance, opposite to the other semiconductors, which chiefly exhibit a parabolic dispersion at the Fermi energy. This linear dispersion is at the origin of the unusual electronic properties of grapheme (Allen et al., 2010).
The electron transport phenomenon is primarily sustained by the filler phase which, at sufficient quantities can form an interconnected network throughout as depicted (Fig. 2). The mechanism of nanocomposite in these materials arises from the disruption of the filler network as a result of mechanical deformation (Allen et al., 2010). The disruption of the network influences the electrical properties of the entire composite and manifests itself as either a rise or decrease in the bulk resistance of the material. The flexible nature of polymeric materials allows for operations over large deformation ranges (strain values as high as 200%). Such a high compliance also allows for them to be integrated on various substrates. In addition, polymer nanocomposites for pressure sensing are simple to manufacture and can be scaled to any size making them one of the primary type of materials being investigated for artificial skins, gait and respiration measurements and other biomechanical measurements.
Graphene has attracted tremendous attention in recent years owing to its exceptional thermal, mechanical, and electrical properties . One of the most promising applications of this material is in polymer nanocomposites, polymer matrix composites which incorporate nanoscale filler materials. Nanocomposites with exfoliated layered silicate fillers have been investigated as early as 1950, but significant academic and industrial interest in nanocomposites came nearly forty years later following a report from researchers at Toyota Motor Corporation that demonstrated large mechanical property enhancement using montmorillonite as filler in a Nylon-6 matrix. Polymer nanocomposites show substantial property enhancements at much lower loadings than polymer composites with conventional micron-scale fillers (such as glass or carbon fibers), which ultimately results in lower component weight and can simplify processing; moreover, the multifunctional property enhancements made possible with nanocomposites may create new applications of polymers (Allen et al., 2010).
Figure 2. Schematics showing how the conductivity of a composite material varies with filler concentration (a) and the expected variance with applied pressure (b).
3. Graphene based nanocomposite and its applications
This polymer functionalized graphene acts as an efficient nanofiller in polymer composites to improve its engineering properties and a small quantity of polymer functionalized graphene improve the mechanical, electronic, optical, thermal and magnetic properties significantly in fig.3. The living radical polymerizations on graphene surface can also produce diverse polymeric architecture promoting graphene from a laboratory to important nanotechnological applications. The conjugated polymer functionalized graphene exhibits typical bistable electrical switching and a nonvolatile rewritable memory effect, with a turn-on voltage of about -1 V and an ON/OFF-state current ratio of more than 103 because of strong ?-? interaction (Yan et al., 2014; Xie et al., 2013; Chae et al., 2014). Some conjugated polymer functionalized graphene like polythiophenes or its derivative composites are widely used in photovoltaic devices and lightemitting diodes etc. Conducting polymers like polyaniline, polypyrrole functionalized graphene composites have a potential application in super capacitors in various field . Polymer functionalized graphene reinforced into the matrix polymer with molecular level dispersion and fine interfacial interaction enhances the strength, stiffness, toughness of the composite (Allen et al., 2010). These types of composites materials may have potential applications in aerospace and naval engineering. Till now, the applications of polymer functionalized graphene composites are not very abrupt and thus it is extremely required of this type of novel materials for stepping forward together with computational studies . We believe that the exploration of polymer functionalized graphene research will bring us much surprise in the future (Allen et al., 2010).
Graphene and its related materials offer lots of superior properties in materials science and are considered to meet all the critical requirements for a practical electrode material due to their unique 2D nanostructure. Therefore, in the work reported here, a few graphene-based nanocomposites have been systematically studied. The synthetic methods, along with the characterizations and the electrochemical properties in supercapacitors.
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