Photonic crystals in biology - NanoTR-VI

PPPP PMohsenP,PP andPoster Session, Thursday, June 17Theme F686 - N11233Study the Effect of Carbon Nanotube Orientation on the Shear Modulus of SWCNT/polymerComposites using Hierarchical MD/FE Multiscale Modeling111,23Abbas MontazeriP P*,P P SadeghiPPReza NaghdabadiP Hasehm Rafii-TabarP12PInstitute for Nano Science and Technology, Sharif University of Technology, Tehran, IranPDepartment of Mechanical Engineering, Sharif University of Technology, Tehran, IranPDepartment of Medical Physics and Biomedical Engineering, and Research Centre for Medical Nanotechnology and Tissue Engineering,Shahid Beheshti University of Medical Sciences, Evin, Tehran, Iran.Abstract- In this paper, a combination of molecular dynamics (MD) and finite element method (FEM) is used to predict the effect of CNTorientation on the shear modulus of nanocomposites containing SWCNTs as reinforcing elements. The results show that in the case of 45 orientation, SWCNTs have the most effect on the shear modulus of polymer composites.Recent experimental and theoretical investigations havedemonstrated that substantial improvements in the mechanicalproperties of polymers can be obtained by using small volumefractions of carbon nanotubes as reinforcing materials.Various properties such as elastic modulus and break strength,yield strength, max strain, buckling behavior, hardness,ductility and toughness, fatigue life and fatigue properties,creep performance and glass transition temperature have beenmeasured in these studies. A noticeable void in currentliterature is the lack of a computational model for determiningthe shear modulus of these nanocomposites. Meanwhile, thestudy of shear deformation is of particular interest as not onlyit is a basic mode of deformation at the microscopic level, butit also could be used to create high orientation throughout alarge cross section of polymer material. Highly orientedpolymers are well-known to exhibit enhanced mechanicalproperties. Furthermore, shear failure is one of the mostfamous failure mechanisms of nanotube reinforcedcomposites. In addition, shear deformation of nanocompositeshas a great effect on the shear-based production techniques ofthese nanostructures like shear mixing methods.The objective of the present article is to analyze the effect ofsingle-walled carbon nanotube alignment on the shearmodulus of SWCNT-reinforced polymer composites using anew hierarchical MD/FE multiscale method. To achieve thisend, first, a transverse-isotropic elastic model of SWCNTs isformulated that combines methods from continuum elasticitytheory and molecular dynamics simulation. This model isemployed to predict the transverse-isotropic elastic propertiesof SWCNTs. MD simulations are used to model themechanical behavior of SWCNTs under axial, torsional andradial loadings. Also, continuum-based models using thelinear elasticity theory were employed to model themechanical behavior of SWCNTs under these loadingconditions. The methodology developed herein combines aunit cell continuum model with MD simulations to determinethe transverse-isotropic elastic constants of SWCNTs. Theseatomically informed carbon nanotubes are used in a finiteelement simulation in the next step to investigate the effect ofsingle-walled carbon nanotube alignment on the shearmodulus of CNT-based nanocomposites. Also, continuumbasedfinite element formulation was implemented to analyzethe polymer matrix. Using this hierarchical MD/FE multiscalemodel, we could obtain the shear properties of thesenanocomposites based on the interatomic interactions ofSWCNT atoms with negligible computational costs.Figure 1. (a) A Schematic illustration of the four loading conditionsof SWCNTs: (a) axial tension, (b) torsion, (c) uniform radial pressure(end view), and (d) non-uniform radial pressure (end view).The results depicted the noticeable effect of adding SWCNTsas reinforcement on the shear deformation of polymers.Increasing the carbon nanotube orientation from 0° caused anincrease in the shear modulus of the polymer up to 45° andthen, the reinforcement role of SWCNT decreased. Note thatin 90°, there was not any change in the shear modulus ofpolymer due to addition of the SWCNT. The fact thatmaximum shear modulus of nanocomposite appears in thecase of 45° carbon nanotube orientation, arises from thetransverse-isotropic elastic properties of SWCNTs as depictedby the hybrid MD/continuum model presented in this work.The results revealed that longitudinal Young’s modulus of theSWCNT was much greater than this elastic constant in thetransverse direction. Hence it was anticipated that in the caseof 45° where the resultant tensile force of the shear forcesimposed on the side walls corresponds to the axial direction ofthe SWCNT, the maximum increase in the shear modulus ofSWCNT-reinforced composites should be obtained. Oursimulation results confirmed the idea.*Corresponding author: a_montazeri@mehr.sharif.edu6th Nanoscience and Nanotechnology Conference, zmir, 2010 749