Molecular dynamics simulation study of mechanical properties of different carbon nanotubes and nanocomposites

Abstract

Carbon nanotube is promising to revolutionize several fields in material science and is a major component of nanotechnology. Nanotubes have a wide range of unexplored potential applications in various technological areas due to their superior mechanical, thermal and electrical properties. In light of these properties, CNTs are expected to be introduced into a wide variety of new materials aimed at applications for various fields, such as high performance composites, biological and chemical sensors, magnetic recording, nano-electronic devices and flat panel displays. In this work, carbon nanotubes of different molecular architectures have been simulated using molecular dynamics simulation. A number of mechanical properties like elastic modulus, bulk modulus, shear modulus and Poisson’s ratio were analyzed to explain the effect of tube radius, tube length and tube chirality on these properties. The numerical results reveal that the value of the Young’s modulus is independent of the tube length, but decreases significantly with increasing tube radius. The results also indicate that the Young’s modulus is insensitive to tube chirality. Polymer/nanotube composites have attracted a lot of attention because the polymer properties are significantly improved. In particular, intensive efforts have been directed toward synthesizing, characterizing, and understanding polymer/CNT composites. Recent investigation has revealed many novel properties of polymer/CNT systems. In this paper, As an effort to explore the effective use of carbon nanotubes as a reinforcing material for advanced nanocomposites with polymer matrices, single-walled carbon nanotubes (MWNTs) were incorporated into five different polymer materials i.e. Polymethyl methacrylate (PMMA), Polystyrene (PS), Polyamide 6 (PA6), Polyethylene (PE) and Polypropylene (PP). Molecular dynamics (MD) simulations were used to predict the properties of these nanocomposites. The properties of interest were Young’s modulus, bulk modulus, shear modulus and compressibility. The Young’s modulus of polymer/CNT composites in the axial direction increases comprehensively when the volume fraction of the CNTs is about 12-16%. The enhanced elastic modulus, bulk modulus and shear modulus of the nanocomposites suggests a strong possibility for the potential use of these nanocomposites in industrial applications. The force-field used in the MD simulation was COMPASS, and COMPASS clearly gave accurate values for the density and moduli of the amorphous polymer matrices (before incorporating CNT) as compared to experiment. In fact, the density predicted by COMPASS was in excellent agreement with reported experimental values of amorphous polymers. Finally, the effective Young’s moduli of these CNT-based composites are compared with values obtained using rule-of-mixture. In case of PE and PP nanocomposites the simulation results are also compared with experimentally available values. The results are in disagreement revealing the fact that rule of-mixture in not an excellent approximate in estimating the overall response of the composite system since it assumes perfect bonding between fiber and matrix. MD simulation gives a close agreement to calculate Young’s modulus of CNT based composite since the results are in good agreement with experimentally available data.