Stone-Wales defect

The possible fatigue failure mechanisms of SWCNT in the composite were also reported (Ren et al., 2004). Possible failure modes mainly include three stages, that is, splitting of SWCNT bundles, kink formation, and subsequent failure in SWCNTs, and the fracture of SWCNT bundles. As shown in Fig. 9.12, for zigzag SWCNT, failure of defect-free tube and tubes with Stone-Wales defect of either A or B mode all resulted in brittle-like, flat fracture surface. A kinetic model for time-dependent fracture of CNTs is also reported (Satapathy et al., 2005). These simulation results are almost consistent with the observed fracture surfaces, which can be reproduced reasonably well, suggesting the possible mechanism should exist in CNT-polymer composites. 

Fig. 9.12 Results of molecular mechanics simulations (a) A Stone-Wales defect (A mode) in a zigzag SWCNT, (b) a Stone-Wales defect (B mode) in a zigzag SWCNT, the bonds with highest potential energy are indicated by arrows. Propagating cracks in (c) A defect-fiee zigzag tube, and (d) defect-lfee armchair tube. Fracture mode of armchair tube with (e) Stone-Wales defect (A mode), and (f) Stone-Wales defect (B mode). Fracture mode of zigzag tube with (g) Stone-Wales defect (A mode), and (h) Stone-Wales defect (B mode) (Huynh et al., 2002. With permission from Wiley)...

In general, differences in chemical bonding and electron configuration between carbon atoms and dopants mandate the deviation from the geometric and electronic equilibrium structure of the aromatic layers in CNTs. As a consequence, topological defects such as Stone-Wales defects are formed with increased probability [37]. 

Fig. 4.4 Molecular model of (a) surface containing positive and negative curvature induced by a pentagon (red) and a heptagon (blue), respectively (b) molecular model of 5-7 defects (yellow) and a Thrower-Stone-Wales defect (green) [82] (c) high-resolution transmission electron microscopy (HRTEM) images of bond rotations V2 (555-777) divacancy, and (d) V2(5555-6-7777) divacancy within graphene scale bar is 1 nm [75].

T.C. Dinadayalane, J. Leszczynski, Stone-Wales defects with two different orientations in (5, 5) single-walled carbon nanotubes A theoretical study. Chem. Phys. Lett. 434, 86 (2007)... 

Figure 3.46 The effect of mechanical strain on carbon nanotubes (a) evolution of undulated defects on the concave side of a bent MWNT, (b) migration of Stone-Wales defects upon tensile stress ( AAAS 1999).

The electric conductivity of carbon nanotubes is largely influenced by the presence of defects. Even effects as modest as axial strain with bond expansion change the band structure. Stone-Wales defects and other imperfections diminish the electric conductivity as well. This effect is especially pronounced for defects with two adjacent vacancies. The resistance of a 400 nm long SWNT, for example, increases by a factor of 1000 if the tube bears as little as 0.03% of these double vacancies. Single vacancies, on the other hand, do not cause such dramatic changes. In any case, however, the free path of the electrons is reduced considerably by the defects (in parts down to a few nanometers). Still, due to the multitude of existing conduction channels, this has no large influence on the overall conductivity. 

S. Letardi, M. Celino, E. Cleri and V. Rosato, Atomic hydrogen adsorption on a Stone-Wales defect in graphite . Surface Science, 496, 33 (2002). 

In this work, we have applied the renormalized monopole-dipole model (RMD) [1] to spherical and icosahedral fullerenes, with the aim to investigate in more detail local effects, i.e. the local electric field and the influence of Stone-Wales defects on the local field in case of spherical fullerenes. A continuous model for a metallic sphere is developed for comparison. 

Fullerenes and carbon onions can be produced by various processes [2-6]. TEM pictures show a wide shape diversity of these particles polyhedral, spherical, highly defected fullerenes with various sizes and number of layers. The spherical structures may contain many defects like (Stone-Wales [7]). In this study we deal with icosahedral regular fullerenes [8] and with very Stone-Wales defective structures that lead to spherical particles [9]. These structures have been optimized with second-generation reactive empirical bond order potential energy (REBO2) [10]. The static dielectric properties are calculated using the RMD... 

The theoretical result obtained for a continuous medium sphere confirms the computational results Eloc(x) x/R and is linearly proportional to the applied field Eo. The dispersion of values for Eioc(x) around the x/R line in Fig. 1 is due to the presence of Stone-Wales defects that induce some dispersion of the direction of Eloc which is perpendicular to the surface on the average. Furthermore, the fullerenes studied here are far from being a continuous surface due to their small size, which explains the deviation with the continuous model. The perspective of this approach is to extend these calculations with a frequency-dependent model by including dynamical polarizabilities and kinetic energy for dipoles and charges. 

Chen, L., Ouyang, Y, Wang, Y, Sun, Y, and Pan, H. 2010. The influence of Stone-Wales defects on magnetic properties in grapheme. Physica E Low-Dimensional Systems and Nanostructures 43 593-597. 

Doudou, B. B., Chen, J., Vivet, A., Poilane, C., and Ayachi, M. 2010. Role of Stone-Wales defects on the functionalization of (8,0) single wall carhon nanotubes by the amine group Ab initio study. Physica E Low-Dimensional Systems and Nanostructures 44 120-123. 

As with any material, the essence of a crystallographic defect affects the material properties. Defects can happen in the form of atomic vacancies. High levels of such defects can drop the tensile strengdi up to 85%. A main example is the Stone Wales defect, which makes a pentagon and... 

Fig. 3.3 The N = 200 dual closed graphene graph modified by the presence of a Stone-Wales defect with two pentagons (red) and two heptagons (green), this defect favors the side regions of the heptagons (pale-blue vertices) whereas the yellow hexagons correspond to unstable vertices. Underlined nodes labels illustrate how closed ends conditions are applied...

Bondons on Nano-Ribbons with Stone-Wales Defects.48... 

GRAPHENIC S TYPE RIBBONS AND THEIR STONE-WALES DEFECTS... 

This algorithm will be next unfolded for the present honeyOcomb systems referenced in the graphene nanoribbons with Stone-Wales defects. 

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