Compressibility and polygonization of single-walled carbon nanotubes under hydrostatic pressure

Single-walled carbon nanotubes show linear elasticity under hydrostatic pressure up to 1.5 GPa at room temperature. The volume compressibility, measured by in situ synchrotron x-ray diffraction, has been determined to be 0.024 GPa (-1). Theoretical calculations suggest that single-walled carbon nanotubes are polygonized when they form bundles of hexagonal close-packed structure and the intertubular gap is smaller than the equilibrium spacing of graphite (002) (d = 3.35 A). It has also been determined that the deformation of the trigonal nanotube lattice under hydrostatic pressure is reversible up to 4 GPa, beyond which the nanotube lattice is destroyed.     

Molecular dynamics simulation on mechanical property of carbon nanotube torsional deformation

In this paper torsional deformation of the carbon nanotubes is simulated by molecular dynamics method. The Brenner potential is used to set up the simulation system. Simulation results show that the carbon nanotubes can bear larger torsional deformation, for the armchair type （10,10） single wall carbon nanotubes, with a yielding phenomenon taking place when the torsional angle is up to 63°（1.1rad）. The influence of carbon nanotube helicity in torsional deformation is very small. The shear modulus of single wall carbon nanotubes should be several hundred GPa, not 1 GPa as others reports.     

AFM detection of the mechanical resonances of coiled carbon nanotubes

We introduce a method for atomic force microscopy (AFM)-based detection of mechanical resonances in helix-shaped multi-walled carbon nanotubes. After deposition on an oxidized silicon substrate, the three-dimensional structure of suspended nanotubes, which bridges an artificially created step on the surface, can be visualized using AFM operating in the non-contact mode. The suspended coiled nanotubes are resonantly excited, in situ, at the fundamental frequency by an ultrasonic transducer connected to the substrate. When the AFM tip is positioned above the coiled nanotube, the cantilever is unable to follow the fast nanotube oscillations. Nevertheless, an oscillation amplitude-dependent signal is generated due to the non-linear force-to-distance dependence. Measurement of the mechanical resonances of the helix-shaped carbon nanotubes can be used to quantitatively determine their elastic properties. Assuming that a coiled nanotube can be modeled as a suspended helix-shaped uniformly thin elastic beam, the obtained resonance frequency is consistent with a Young's modulus of 0.17ǂ.05 TPa.     

Structural and electronic properties of carbon nanotubes under hydrostatic pressures

We studied the structural and electronic properties of carbon nanotubes under hydrostatic pressures based on molecular dynamics simulations and first principles band structure calculations. It is found that carbon nanotubes experience a hard-to-soft transition as external pressure increases. The bulk modulus of soft phase is two orders of magnitude smaller than that of hard phase. The band structure calculations show that band gap of (10, 0) nanotube increases with the increase of pressure at low pressures. Above a critical pressure (5.70GPa), band gap of (10, 0) nanotube drops rapidly and becomes zero at 6.62GPa. Moreover, the calculated charge density shows that a large pressure can induce an {sp}²-to-{sp}³ bonding transition, which is confirmed by recent experiments on deformed carbon nanotubes.     

Mechanical Properties of Single-Walled （5,5） Carbon Nanotubes with Vacancy Defects

First-principles simulation is used to investigate the structural and mechanical properties of vacancy defective single-walled （5,5） carbon nanotubes. The relations of the defect concentration, distribution and characteristic of defects to Young＇s modulus of nanotubes are quantitatively studied. It is found that each dangling-bond structure （per supercell） decreases Young＇s modulus of nanotube by 6.1% for symmetrical distribution cases. However the concentrative vacancy structure with saturated atoms has less influence on carbon nanotubes. It is suggested that the mechanical properties of carbon nanotubes depend strongly upon the structure and relative position of vacancies in a certain defect concentration.     

Facile fabrication of novel cyclomatrix-type polyphosphazene nanotubes with active hydroxyl groups via an in situ template approach

Novel polyphosphazene nanotubes with active hydroxyl groups were fabricated via an in situ template approach under ultrasonic irradiation. SEM and TEM results indicated that the nanotubes were uniform with length of several micrometers, inner diameter of ca. 20 nm and outer diameter of 60-80 nm. FTIR spectra revealed that the content of the hydroxyl groups on the nanotube surface was dependent on the feed ratio of hexachlorocyclotriphosphazene (HCCP) to 4,4′-sulfonyldiphenol. The successful esterification of polymer nanotubes with benzoxy chloride demonstrated the high reactivity of the hydroxyl groups. The method employed here might provide a simple and effective way to prepare functional nanotubes used for biological applications.     

Polyurethane‐Carbon Nanotube Nanocomposites Prepared by In‐Situ Polymerization with Electroactive Shape Memory

In‐situ polymerization was employed to achieve well‐dispersed carbon nanotube‐reinforced polyurethane composites. In‐situ polymerization showed predominant as primarily dispersal of carbon nanotubes in the matrix polymer according to scanning electron microscopy (SEM) observation and atomic force microscopy (AFM) images. Differential scanning calorimetry (DSC) results suggested that the addition of multi walled nanotubes (MWNTs) into polyurethane increased the rate of crystallization, this effect being more significant in polyurethane (PU)‐MWNT composite, which was prepared by an in‐situ polymerization process. The composites obtained by in‐situ polymerization showed enhanced mechanical properties as well as good electroactive shape memory. The original shape of the sample was almost recovered with bending mode when an electric field of 50 V was applied.     

高压下碳纳米管的X射线衍射研究

 用同步辐射原位高压能散X射线衍射技术,对碳纳米管进行了结构和物性的研究,压力达50.7 GPa。在室温常压下,碳纳米管的结构和石墨的hcp结构相似,其(002)衍射线的面间距为d₀₀₂=0.340 4 nm,(100)衍射线的面间距为d₁₀₀=0.211 6 nm。从高压X射线衍射实验看到,当压力升到8 GPa以上时,(002)线变宽变弱,碳纳米管部分非晶化。而当压力从10 GPa或20 GPa卸压至零时,(002)线部分恢复。但当压力升高至最高压力50.7 GPa时,碳纳米管完全非晶化,而且这个非晶化相变是不可逆的。用Birch-Murnaghan方程拟合实验数据,得到体弹模量为K₀=(54.3±3.2)GPa（当K′₀=4.0时）。     

C<Subscript>60</Subscript> fullerene decoration of carbon nanotubes

A new fully carbon nanocomposite material is synthesized by the immersion of carbon nanotubes in a fullerene solution in carbon disulfide. The presence of a dense layer of fullerene molecules on the outer nanotube surface is demonstrated by TEM and XPS. Fullerenes are redistributed on the nanotube surface during a long-term action of an electron beam, which points to the existence of a molecular bond between a nanotube and fullerenes. Theoretical calculations show that the formation of a fullerene shell begins with the attachment of one C₆₀ molecule to a defect on the nanotube surface.     

Novel superhard carbon: C-centered orthorhombic C8

A novel carbon allotrope of C-centered orthorhombic C(8) (Cco-C(8)) is predicted by using a recently developed particle-swarm optimization method on structural search. Cco-C(8) adopts a sp(3) three-dimensional bonding network that can be viewed as interconnected (2,2) carbon nanotubes through 4- and 6-member rings and is energetically more favorable than earlier proposed carbon polymorphs (e.g., M carbon, bct-C(4), W carbon, and chiral C(6)) over a wide range of pressures studied (0-100 GPa). The simulated x-ray diffraction pattern, density, and bulk modulus of Cco-C(8) are in good accordance with the experimental data on structurally undetermined superhard carbon recovered from cold compression of carbon nanotube bundles. The simulated hardness of Cco-C(8) can reach a remarkably high value of 95.1 GPa, such that it is capable of cracking diamond.