MD Simulation Of Radial Mechanical Properties Of Modified Carbon Nanotubes

Nanomaterial is one kind of the most promising materials in the21st century. It isdemonstrated that nanomaterial always shows peculiar physical and chemical properties,which will change human life in the near future. Using the molecular mechanics (MM) andmolecular dynamics (MD) methods this paper systemically investigated the influences ofseveral factors on the radial collapse and elasticity of carbon nanotubes (CNTs), includingchirality, defect, covalent modification and non-covalent modification. Due to the mechanicalbehavior of CNT is different from traditional materials, it is essential to in-depth and fullystudy and understand the mechanical properties of CNT for designing CNT-based nano-sizedinstrument and developing nano-sized electromechanical systems.The main research content and academic contributions are as follows:1. The influence of covalent modification on the radial collapse and elasticity ofsingle-walled CNTs (SWNTs) under hydrostatic pressure was investigated. It is found thatthe radial collapse and elasticity of SWNTs modified by functional group are largelydependent on the polarity and concentration of functional group; by comparing the collapseprocess of the intrinsic and modified SWNTs, we discover that the coulomb energy and vander Waals (vdW) energy can influence the stability of collapsed SWNTs modified withfunctional groups.It is found that the fluorine (-F) modified SWNT (F-SWNT), on which2.5-5.0%of theatoms are attached to-F groups, can sustain the original elasticity of the intrinsic SWNT, andthe pressure needed to collapse the F-SWNT increases by11.3-21.8%. Functional groupssuch as hydroxyl groups, amino groups and carboxylic groups can increase the pressureneeded to collapse the modified SWNTs, but decrease their radial elasticity. Therefore, theF-SWNT, due to the higher collapse pressure, are ideal fillers for nanocomposites for high load mechanical support.2. The influences of SWNT chirality, Stone-Wales (SW) defect and defect orientationon the radial collapse and elasticity of SWNTs were investigated using MM and MDsimulations. It is found that the radial collapse of intrinsic and SWNTs with defect can beinfluenced by the arrangement of hexagons, pentagons and heptagons consisted of thesp2-hybridized carbon atoms. We introduce a model for SWNTs deformed in the radialdirection according to the projection of the C-C bond along the bending direction. The modelis validated for defect-free SWNTs and is then used to study the radial collapse of SWNTswith SW defects. The effects of chirality and SW defect on the radial collapse of SWNTs canbe understood by the model.It is found that the collapse pressure (Pc) of the SWNT(10,10) is13.75times higher thanthat of the SWNT(17,0). Moreover, the SWNT(10,10) with SW defect is easier to collapsecompared to the intrinsic SWNT(10,10), while the SWNT(17,0) with SW defect is moredifficult to collapse compared to the intrinsic SWNT(17,0); the SW2defect makes PcofSWNT(10,10) decrease by11.0%, while the SW4defect makes Pcof SWNT(17,0) increaseby100.0%. The strong sensitivity of radial collapse of SWNTs to chirality and SW defect canprovide some guidance for high load structural applications of SWNTs. Defect anddeformation can usually change the electrical properties of SWNTs, radial deformationcharacteristic of SWNT with defect can provide a foundation for further investigating theinfluences of defects and radial deformation on the electrical properties of SWNTs.3. The high pressure behavior of SWNTs (r=6.78) filled with fullerenes (C60@SWNTs)was investigated using MD and MM simulations. It is found that the C60filling can increasethe Pcof intrinsic SWNTs and optimize the radial elasticity of SWNTs. The C60fillingincreases the Pcof zigzag SWNTs by a factor of~25, and the Pcof armchair SWNTs by afactor of~5. What’s more, the C60filling number can modulate SWNT’s Pcand radialelasticity. An inelastic SWNT(17,0) can be transformed into a superelastic SWNT(17,0) byfilling C60into SWNTs. Moreover, the original shape of SWNTs can be recovered quicklyupon unloading; the filling does not affect the structural integrity of SWNTs. Due to theresistance to high pressure of C60@SWNTs, it can be used as scaffold of the composite or complex mechanics materials. Radial deformation and filling can change the electricalproperties of SWNTs, in view of the recoverability of C60@SWNTs upon unloading,C60@SWNTs can be used to prepare nanoelectronic devices used in the nanoelectromechanical systems.The radial collapse and elasticity of SWNTs (r>6.78) filled with C60was also studiedsystematically. It is found that SWNTs filled with C60can collapse under low pressure, whichare consistent with the experimental results. We describe the interaction between SWNT andC60with Lennard-Jones potential to reveal the physical mechanism of the C60@SWNTs’sradial collapse, which can provide a theoretical guidance for the experimental result.4. The radial collapse and elasticity of SWNTs filled with graphene (GN) wasinvestigated. It is found that the vdW interaction and π-π stacking interaction between GNand SWNTs make the GN form a spiral structure inside SWNTs. The GN filling caneffectively enhance the radial collapse and elasticity of SWNTs.The filling process of polymer inside SWNTs was studied. It is demonstrated that therigidity and aromatic ring of polymer influence the morphology of the polymer inside SWNT.The rigid polymer behaves the spiral structure inside the SWNT; semi-flexible polymerdemonstrates S-type distribution inside SWNT; flexible polymer can fill the SWNT, but bedisordered inside SWNT.It is found that the polymer filling can improve the radial collapse of SWNTs. Therigidity and aromatic ring of polymer influence the radial elasticity of SWNT filled withpolymer. In view of resistance to high pressure of filled SWNTs, it can be used as a skeletonof high load composites.