Molecular modelling of graphene nanoribbons on the effect of porosity and oxidation on the mechanical and thermal properties

Abstract

Graphene is considered as the most promising nanomaterial of the recent decades given the huge amount of studies that have been performed to characterize its outstanding properties and in searching of novel applications. Following this tendency, this study covers the modelling of graphene nanoribbons (GNRs) with the aim of analyzing the effect of porosity and oxidation on the tensile mechanical properties and in-plane thermal conductivity through molecular dynamics (MD). Using quasi-static simulations the mechanical properties were evaluated in first place. A ‘hardening’ mechanism was observed for GNRs at porosities below 1%, i.e. perfect or near-perfect GNRs, by which the GNRs could withstand higher loading levels. This hardening effect was manifested in the carbon network by the generation of dislocation lines formed by pentagon-heptagon pairs (5–7 defects), which acted as a stress reliever. The failure of GNRs was produced as a tearing mechanism with cracks growing along the armchair or zigzag directions. The porosity affected all the analysed tensile mechanical properties (i.e., Young’s modulus, Poisson’s ratio, tensile strength and deformation at break), but with different tendency in the fracture properties due to the presence or absence of hardening behaviour in the GNRs. Nevertheless, the oxidation affected only the tensile modulus and Poisson’s ratio but not to the tensile strength and deformation at break. The thermal conductivity of the GNRs was affected either by the porosity and oxidation. Pores and oxidation groups acted as phonon scatterers since they disrupted the carbon network by the generation of vacancies or out-of-plane carbons, respectively, which decreased the phonon mean free path and thus the thermal conductivity. In conclusion, the porosity and oxidation of GNRs greatly determine the tensile mechanical properties and in-plane thermal conductivity of such materials and must be considered when tuning the synthetic pathways. Graphical abstract The effect of porosity and oxidation on the tensile mechanical and thermal conductivity properties of graphene nanoribbons are evaluated through molecular dynamics simulations.