Effect of temperature on elastic properties of CNT-polyethylene nanocomposite and its interface using MD simulations

This paper investigates the effect of temperature on the elastic modulus of carbon nanotube-polyethylene (CNT-PE) nanocomposite and its interface using molecular dynamics (MD) simulations, by utilizing the second-generation polymer consistent force field (PCFF). Two CNTs-armchair and zigzag-were selected as reinforcing nano-fillers, and amorphous PE was used as the polymer matrix. For atomistic modelling of the nanocomposite, the commercially available code Materials Studio 8.0 was used and all other MD simulations were subsequently performed using the open source code Large-Scale Atomic/Molecular Massively Parallel Simulator (LAMMPS). To obtain the elastic modulus of the nanocomposite, stress-strain curves were drawn at different temperatures by performing uniaxial deformation tests on the nanocomposite material, whereas the curvatures of the interfacial interaction energy vs. strain curves were utilized to obtain Young's modulus of the interface. In addition, the glass transition temperatures of the polymer matrix and nanocomposites were also evaluated using density-temperature curves. Based on the results, it is concluded that, irrespective of temperature condition, a nanocomposite reinforced with CNT of larger chirality (i.e., armchair) yields a higher value of Young's modulus of the nanocomposite and its interface. It was also found that, at the phase transition (from a glassy to a rubbery state) temperature (i.e., glass transition temperature), Young's moduli of the polymer matrix, nanocomposite, and its interface drop suddenly. The results obtained from MD simulations were verified with results obtained from continuum-based rule-of-mixtures.