Kausala Mylvaganam

Fabrication and Application of Polymer Composites Comprising Carbon Nanotubes

Carbon nanotubes are being used in place of carbon fibers in making composites due to their high strength, high aspect-ratio and excellent thermal and electrical conductivity. Although carbon nanotubes were discovered more than a decade ago, works on preparation of satisfactory composites reinforced by carbon nanotubes have encountered difficulties. This review will discuss some registered patents and relevant papers on the fabrication of carbon nanotube-polymer composites on improving material properties such as electrical conductivity, mechanical strength, and radiation detection which have a broad range of applications in nano-electronic devices, and space and medical elements.

Evolution of metastable phases in silicon during nanoindentation: mechanism analysis and experimental verification

This paper explores the evolution mechanisms of metastable phases during the nanoindentation on monocrystalline silicon. Both the molecular dynamics (MD) and the in situ scanning spreading resistance microscopy (SSRM) analyses were carried out on Si(100) orientation, and for the first time, experimental verification was achieved quantitatively at the same nanoscopic scale. It was found that under equivalent indentation loads, the MD prediction agrees extremely well with the result experimentally measured using SSRM, in terms of the depth of the residual indentation marks and the onset, evolution and dimension variation of the metastable phases, such as beta-Sn. A new six-coordinated silicon phase, Si-XIII, transformed directly from Si-I was discovered. The investigation showed that there is a critical size of contact between the indenter and silicon, beyond which a crystal particle of distorted diamond structure will emerge in between the indenter and the amorphous phase upon unloading.

Ballistic resistance capacity of carbon nanotubes

Carbon nanotubes have high strength, light weight and excellent energy absorption capacity and therefore have great potential applications in making antiballistic materials. By examining the ballistic impact and bouncing-back processes on carbon nanotubes, this investigation shows that nanotubes with large radii withstand higher bullet speeds and the ballistic resistance is the highest when the bullet hits the centre of the CNT; the ballistic resistance of CNTs will remain the same on subsequent bullet strikes if the impact is after a small time interval.

Analysis and modeling of the high vacuum scanning spreading resistance microscopy nanocontact on silicon

Within this paper, the authors propose a refined high vacuum scanning spreading resistance microscopy (HV-SSRM) electromechanical nanocontact model based on experimental results as well as molecular dynamics (MD) simulation results. The formation under the tip of a nanometer-sized pocket of β-tin, a metastable metalliclike phase of silicon (also named Si-II), acting as a virtual probe is demonstrated. This gives a reasonable explanation for the superior SSRM spatial resolution as well as for the electrical properties at the Schottky-like SSRM contact. Moreover, the impact of the doping concentration on the plastic deformation of silicon for different species using micro-Raman combined with indentation experiments is studied. In order to elucidate the superior results of SSRM measurements when performed under high vacuum conditions, the impact of humidity on the mechanical deformation and Si-II formation is also analyzed using MD and SSRM experimental results.

Molecular simulations of the large conductance mechanosensitive (MscL) channel under mechanical loading

The MscL channel is a mechanosensitive channel which is gated by membrane stress or tension. Here, we describe a series of simulations which apply simulated mechanical stress to a molecular model of the MscL channel using two methods – direct force application to the transmembrane segments, and anisotropic pressure coupling. In the latter simulations, pressures less than that equivalent to a bilayer tension of 12 dyn/cm did not cause the channel to open, while pressures in excess of this value resulted in the channel opening. These results are in approximate agreement with experimental findings.

Deformation-promoted reactivity of single-walled carbon nanotubes

This paper investigates the effect of mechanical deformation of a single-walled carbon nanotube (SWNT) on its reactivity with hydrogen and alkyl radicals. The influence of individual loading modes was explored with the aid of molecular dynamics simulation for deformation and quantum mechanics analysis for reaction. The study discovered that the radicals bind to the deformation-induced ridges tightly with high binding energies, but at the deformation-flattened surface the binding energy becomes even lower than that of a non-deformed nanotube. At a low strain energy of ~2 kJ mol−1 a nanotube deformed by central loading gives a stronger binding with a hydrogen atom to the ridge, while at a little higher strain energy pure bending and torsion give rise to a better binding. The above findings show that mechanical deformation of carbon nanotubes can strongly promote their reactivity and form stronger covalent bonds with radicals.

Energy Absorption Capacity of carbon nanotubes under ballistic impact

Carbon nanotubes have great potential applications in making ballistic-resistance materials. This letter analyzes the impact of a bullet on nanotubes of different radii in two extreme cases. For a nanotube with one end fixed, the maximum nanotube enduring bullet speed increases and the energy absorption efficiency decreases with the increase in relative heights at which the bullet strikes; these values are independent of the nanotube radii when the bullet hits at a particular relative height. For a nanotube with both ends fixed, the energy absorption efficiency reaches minimum when the bullet strikes around a relative height of 0.5.

Effect of oxygen penetration in silicon due to nano-indentation

This paper aims to explore the effect of O2 on the nano-indentation of diamond cubic silicon using molecular dynamics simulation. Obtained with the aid of the Tersoff potential for Si–Si interactions and the Morse potential for all other interactions, the results show that on indentation, the O2 molecule in the appropriate position and orientation dissociates into oxygen atoms, penetrates into the subsurface region and forms chemical bonds with silicon atoms. The penetration of oxygen atoms attracts silicon atoms, causing substantial disorder in the substrate.

Residual stress induced atomic scale buckling of diamond carbon coatings on silicon substrate

This paper investigates the atomic scale buckling of diamond carbon coatings on silicon substrate caused by residual stresses in two orthogonal directions. It was found that different buckling patterns occurred when the ratio of the residual stresses in the two directions were changed. The size of wrinkles increased on going from uniaxial to biaxial compression of the residual stress fields. A telephone-cord like buckling mode took place when the residual stresses were bi-axially equal.

The Intrinsic Frictional Property of Carbon Nanotubes

This paper aims to provide an understanding of the intrinsic frictional behaviour of CNTs under contact sliding by eliminating the possible effects of CNT rolling and slipping. Two critical steps towards the mechanism exploration were carried out: (1) the development of a new deposition method for CNT film fabrication, which allows the manufacture of densely packed, highly entangled CNT films to be firmly bonded on solid substrates for contact sliding testing; and (2) the theoretical understanding of the frictional behaviour of CNTs using the molecular dynamics analysis. The investigation clarified the controversial arguments in the literature and concluded that CNT films can be used as a superior solid lubricant with an ultra-low coefficient of friction of around 0.01.