Mechanical characterization of polymer-grafted graphene PEG nanocomposites using molecular dynamics

It is known that most polymers exhibit poor interfacial compatibility with graphene sheets. Modification of graphene's surface by functionalization with small polymer chains from the same building blocks as the matrix polymer improves the compatibility of graphene in polymeric materials. In this paper, the mechanical behaviour of polyethylene glycol (PEG) nanocomposites with graphene grafted with polymeric chains under tensile and compression is investigated using molecular dynamics. The influence of the functional groups (-NH2 and -OH) that bond the polymer chain to graphene is analysed. It is found that the system containing the -NH2 functional group showed lower mechanical properties than the system containing the -OH functional group. The mechanical properties of five PEG-nanocomposites are investigated: PEG/G, PEG/GNH-1PEG-S, PEG/GNH-2PEG-L, PEG/GNH-1PEG-S-NH2, PEG/GO-1PEG-S. The radius distribution function values and the variation of interfacial interaction energy are also examined. It is shown that functionalization of the graphene sheet increases the magnitude of the interaction energy, and it also reveals higher adhesion between graphene surface and PEG matrix. It is found that the mechanical properties of PEG are mostly improved in the longitudinal direction (reinforcement up to 43 %). Despite the high interaction between the nanofiller and PEG matrix, the low intrinsic properties of the nanofiller, namely Young's modulus, as well as the rupture of the graphene sheet during the deformation process deteriorated the mechanical properties of the nanocomposite. The presence of polymeric chains grafted to graphene improves the adhesion between the graphene surface and the polymeric matrix but decreases its mechanical properties.