Carbon nanotube molecular mechanics

Here we consider a zigzag type (18, 0) carbon nanotube. Molecular mechanics simulations reveal that a crack expands along the circumference of a zigzag SWNT perpendicular to the loading direction, thus the time-to-failure of an intact nanotube, t, is the summation of the lifetime, of each individual C-C... 

Han SS, Lee HM (2003) Molecular dynamics simulation of zigzag single-walled carbon nanotube closing mechanisms. Met Mater Int 9 99-105... 

Ding, L. et al. (2005) Molecular characterization of the cytotoxic mechanism of multiwall carbon nanotubes and nano-onions on human skin fibroblast. Nano Letters, 5 (12), 2448-64. 

CNTs have been studied for cancer therapies despite the fact that these have been shown to accumulate to toxic levels within the organs of diverse animal models and different cell lines (Fiorito et al., 2006 Tong and Cheng, 2007). The molecular and cellular mechanisms for toxicity of carbon nanotubes have not been fully clarified. Furthermore, toxicity must be examined on the basis of multiple routes of administration (i.e., pulmonary, transdermal, ocular, oral, and intravenous) and on multiple species mammals, lower terrestrial animals, aquatic animals (both vertebrates and invertebrates), and plants (both terrestrial and aquatic). A basic set of tests for risk assessment of nanomaterials has been put forward (Nano risk framework). 

Because of their exceptional mechanical, electronic and optical properties, carbon nanotubes (CNTs) are amongst the most studied nanomaterials, particularly when used in combination with other molecular systems. 

It was found that 5-nm-thick resist-mask polysilane films worked well in a direct lithography process on silicon substrates, resulting into a line width of 40 nm prepared by scanning probe microscope lithography, using a carbon nanotube tip.57 Thin PMPS films of 6—8 nm, with a molecular weight of 30,000 were prepared by spin casting and cured at 150°C to obtain a smooth surface. It has been interpreted that moisture was essential for the oxidation of the polysilane. The proposed mechanism involved dissociation of Si-Si bonds in polysilane by the electron injection from the carbon nanotube tip catalyzed by moisture. 

G.E. Froudakis, Hydrogen interaction with single-walled carbon nanotubes A combined quantum-mechanics/molecular-mechanics study. Nano Lett. 1, 179 (2001)... 

The DNA-carbon nanotube interaction is a complicated and dynamic process. Many studies on this subject have been pursued through a series of techniques, including molecular dynamic simulation, microscopy, circular dichroism, and optical spectroscopy.57,58 Although the detailed mechanism is not fully understood at present, several physical factors have been proposed to be driving DNA-carbon nanotube interactions,46,59-61 such as entropy loss due to confinement of the DNA backbone, van der Waals and hydrophobic (rr-stacking) interactions, electronic interactions between DNA and carbon nanotubes, and nanotube deformation. A recent UV optical spectroscopy study of the ssDNA-SWNT system demonstrated experimentally that... 

The mechanical properties of various types of carbon nanotubes have been extensively studied by both theoretical and experimental studies. In 1993, Overney et al. firstly calculated the rigidity of short SWNTs and the calculated Young s modulus was estimated to be about 1500 GPa, similar to that of graphite (65). Then a range of studies predicted that the Young s modulus of carbon nanotubes was approximately 1 TPa (66). The tensile strength of SWNTs was also estimated from molecular dynamics simulation to be 150 MPa (67). 

In this entry, the principal chemical features of defect populations (defect chemistry) will be described from the restricted viewpoint of crystalline inorganic solids. The influence of defects upon mechanical properties will be excluded and defects that may have greatest relevance to physical properties will be treated from the point of view of chemical importance. Defects in molecular crystals and amorphous and glassy solids will be omitted see Noncrystalline Solids), as will the important areas of alloys see Alloys), thin films see Thin Film Synthesis of Solids), and carbon nanotubes and related nanoparticles see Carbon Fullerenes). References to the literature before 1994 are to be found in the corresponding article in the first edition of this Encyclopedia. ... 

Molecules that rotate in a certain direction and actuators based on carbon nanotubes are explained. Mechanical control of molecular recognition and mechanical movement based on molecular recognition are also discussed. 

The structure and properties of C2o (8,8) CNT system are explored by quantum chemical and molecular mechanic calculations. The change of the barrier for relative motion of fullerene along the carbon nanotube axis at the Peierls transition is found. The changes of dynamical behavior of the system C2o (8,8) CNT at the transition are discussed. 

A possibility of encapsulation of small fullerenes inside carbon nanotubes (CNTs) was considered recently [1], It was shown that the armchair (8,8) nanotube is the smallest CNT which can encapsulate the fullerene C20 [1]. We use the semiempirical PM3 molecular orbital method with periodic boundary conditions along the nanotube axis [2] to study the structure and properties of the system C2o (8,8) CNT. The PM3 method [3] was used previously to study the fullerene C20 [4] and to calculate the Kekule structure of the ground state of the (5,5) CNT [5]. To explore the relative motion of C20 inside the (8,8) CNT we additionally implemented molecular mechanics (MM+) calculations [6]. 

In order to minimize effects of nanotube edges in our molecular mechanics calculations we have chosen five unit cells (480 carbon atoms total) of (8,8) CNT. The calculated dependence of the interaction energy between the fullerene C20 and the (8,8) CNT on the fullerene displacement along the CNT axis is shown in Fig. 3. The calculated period of this dependence is a half of the translational period of the Kekule structure (Fig. 1). The small difference between two barriers in Fig. 3 is due to the edge effects. Correspondingly, the frequency of small oscillation of fullerene C20 along the CNT axis near the minimum of potential energy is v 60 GHz. 

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