Effect of Grafting Nanofillers with Polymer Chains in Polyetherimide-Graphene Nanocomposites

Polymer nanocomposites (PNCs) are expected to harness the properties of both matrix materials and nanofillers and such success relies on the synergy between the two. However, the development of PNCs faces two major challenges. One is that the nanofillers usually tend to aggregate. The other is that the introduction of nanofillers may generate weak interfaces with matrix materials where fracture can initiate upon mechanical loading. We recently experimentally studied PNCs composed of polyetherimide (PEI) as the matrix and reduced graphene oxide (rGO) nanoparticles as the fillers. Compared to unmodified nanofillers, rGO nanoparticles with PEI chains grafted along their edge planes led to nanocomposites with enhanced mechanical properties (e.g., Young's modulus). Large-scale all-atom molecular dynamics simulations were then used to reveal the molecular mechanisms underlying the experimental observation. The interface between the edge plane of rGO particles and the polymer matrix are identified as a weak interface. By grafting the edge plane of rGO nanofillers with PEI chains, the weak interface is removed, leading to enhanced compatibility between the nanofillers and polymer matrix. Furthermore, some PEI chains grafted to the edge plane of a rGO nanoparticle bend over and get adsorbed on its basal plane, which interacts more favorably with PEI chains. Such adsorbed chains protect the rGO nanoparticles and prevent their aggregation within the PNCs, thus enhancing their dispersion within the matrix and leading to improved mechanical performance of the nanocomposites.