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Carbon Nanotubes: Preparation and Surface Modification for Multifunctional Applications
Published in Vineet Kumar, Praveen Guleria, Nandita Dasgupta, Shivendu Ranjan, Functionalized Nanomaterials I, 2020
Jingyao Sun, Jing Zhu, Merideth A. Cooper, Daming Wu, Zhaogang Yang
Another type of covalent modification method of CNTs is defect modification (Strategy B in Figure 6.7). Chemical transformation of defect sites is utilized in this process for CNT modification. Here, the defect sites can be the holes in the sidewall or end-tips of CNTs, oxygenated sites, and pentagonal or heptagonal irregularities in hexagonal graphene frames (e.g., the Stone–Wales defect, also known as 7-5-5-7 defect, as seen in Figure 6.8). Stone–Wales defect on the sidewall of a CNT: (-) Thirteen-layer defect-free tube model and (α) Thirteen-layer defective tube model (Reproduced with permission (Lu, Chen, and Schleyer, 2005).).
CARBON NANOTUBES: UPDATE AND NEW PATHWAYS
Published in Rainer Wolf, Gennady E. Zaikov, A. K. Haghi, Pathways to Modern Physical Chemistry, 2016
F. RAEISI, S. PORESKANDAR, SH. MAGHSOODLOU, A. K. HAGHI
Recently, an interesting mode of plastic behavior has been predicted in nanotubes.97 It is suggested that pairs of 5-7 (pentagon-heptagon) pair defects, called a Stone-Wales defect,98 in sp2 carbon systems, are created at high strains in the nanotube lattice and that these defect pairs become mobile. This leads to a step-wise diameter reduction (localized necking) of the nanotube. These defect pairs become mobile. The separation ofthe defects creates local necking of the nanotube in the region where the defects have moved. In addition to localized necking, the region also changes lattice orientation (similar in effect to a dislocation passing through a crystal). This extraordinary behavior initiates necking, but also introduces changes in helicity in the region where the defects have moved (similar to a change in lattice orientation when a dislocation passes through a crystal). This extraordinary behavior could lead to a unique nanotube application: a new type of probe, which responds to mechanical stress by changing its electronic character. High temperature fracture of individual nanotubes under tensile loading has been studied by molecular dynamics simulations.99 Elastic stretching elongates the hexagons until, at high strain, some bonds are broken. This local defect is then redistributed over the entire surface, by bond saturation and surface reconstruction. The final result of this is that instead of fracturing, the nanotube lattice unravels into a linear chain of carbon atoms. Such behavior is extremely unusual in crystals and could play a role in increasing the toughness by increasing the energy absorbed during deformation of nanotube-filled ceramic composites during high temperature loading.
Functionalization of Graphite and Graphene
Published in Titash Mondal, Anil K. Bhowmick, Graphene-Rubber Nanocomposites, 2023
Akash Ghosh, Simran Sharma, Anil K. Bhowmick, Titash Mondal
In quest of understanding the functionalization of graphene and graphitic materials, it is important to understand the structure of the graphene and graphitic material. The contribution of thermodynamics and kinetics factors toward modification of graphene is critical to understand. Ideally, functionalization of graphene can be targeted at the basal plane or at the edges of the material. However, modification at the basal plane of the graphene is tricky. Modification at the basal plane results in the formation of high energy radicals. Thermodynamically, the formation of such radicals is highly unfavorable. In terms of the kinetic purview, change in hybridization of modified carbon (post-modification) introduces geometric constraints. Hence, modification of graphene at the basal plane is challenging task, except under specific conditions. One of such specific case is the defect specific modification of the graphene. Graphene and graphitic materials demonstrate topological isolated defects in their ring, commonly referred to as the Stone–Wales defect. In an ideal situation, graphene and graphitic materials demonstrate a perfect array of hexagonal ring system. However, in the case of Stone–Wales defect, one carbon-carbon bond of the ring is flipped by 90° (participation of four hexagonal rings) and results in the formation of two heptagonal and two pentagonal rings in the system as shown in Figure 4.2a. The other common type of defect pertains to the missing atom in the ring. Vacancy of atoms in the framework leads to Jahn–Teller distortion at those sites. This results in the saturation of three dangling bonds over the vacant site, while the other bond remains further apart due to the introduction of the constraint in the geometry. This results in the formation of five- and nine-membered ring in the skeleton as shown in Figure 4.2b. Defect specific modification of graphene and its analogs is possible and will be discussed in detail in the later section of the chapter. In contrary to the basal plane modification, edge specific modifications can be an easier route for modification of the graphene and its analogs. This is so because the C=C bonds at the edges are more strained and surface modifications favor the conversion of sp2 hybridized carbon of graphene to take up a more relaxed sp3 hybridized form.
Atomistic simulation of crack propagation in CNT reinforced nanocrystalline aluminum under uniaxial tensile loading
Published in Philosophical Magazine, 2021
Pokula Narendra Babu, Saurabh Dixit, Snehanshu Pal
The parallel crack's fracture mechanism in (30,30) CNT is demonstrated with atomic snapshots of CSP feature at low temperature as shown in Figure 8. The hexagonal shape of the CNT structure (carbon atoms) has been distorted into five and seven carbon atoms due to the Stone–Wales defect formation, as displayed in Figure 8. It causes the fracture of CNT by reducing the diameter and increasing length; similar findings have been reported in the literature [41,68]. As the loading increases, the distortion rate is increased, and it causes to full fracture of the CNT by diminishing the CNT strength as per Figure 8. The fracture mechanism is similar for three deformation temperatures of (5,5) and (15,15) CNTs embedded NC Al specimens.