Interfacial characteristics of polymer nanocomposites represent a crucial aspect to understand their global properties and to evaluate the interaction between nanofillers and matrix. In this work we used a molecular dynamics (MD) approach to characterize the interfacial region at the atomistic scale of graphene-based polymer nanocomposites. Three different polymer matrixes were considered, polylactic acid (PLA), polypropylene (PP) and epoxy resin (EPO), which were reinforced with three types of graphene fillers: pristine graphene (G), graphene oxide (GO) and reduced graphene oxide (rGO). In particular, the compatibility of the nanofillers in polymer matrixes were evaluated in terms of the interaction energy, while the interfacial thermal resistance (Kapitza resistance) between matrices and fillers was calculated with a nonequilibrium molecular dynamics (NEMD) method. Results showed that the oxidation degree plays an important role on the studied properties of the interfacial region. In particular, it was observed that the Kapitza resistance is decreased in the oxidized graphene (GO and rGO), while interaction energy depended on the polarity of the polymer matrix molecules and the contribution of the Coulombic component.

In polymer nanocomposites, the interface region between the matrix and the fillers has been identified as a key interaction region that strongly determines the properties of the final material. Determining its structure is crucial from several points of view, from modeling (i.e., properties prediction) to materials science (i.e., understanding properties/structure relationships). In the presented paper, a method for characterizing the interface region of polymer nanocomposites is described using molecular dynamics (MD) simulations. In particular, the structure of the polymer within the interface region together with its dimension in terms of thickness were analyzed through density profiles. Epoxy resin nanocomposites based on diglycidyl ether of bisphenol A (DGEBA) were studied using this approach, and the interface region with triple walled carbon nanotubes (TWCNT) and carbon fibers (CF) was characterized. The effect of carbon nanotube diameter, type of hardener, and effect of epoxy resin cross-linking degree on interface thickness were analyzed using MD models. From this analysis no general rule on the effect of these parameters on the interface thickness could be established, since in some cases overlapping effects between the analyzed parameters were observed, and each specific case needs to be analyzed independently in detail. Results show that the diameter has an impact on interface thickness, but this effect is affected by the cross-linking degree of the epoxy resin. The type of hardener also has a certain influence on the interface thickness.

This research addresses the need for a multiscale model for the determination of the thermophysical properties of nanofiller-enhanced thermoset polymer composites. Specifically, we analyzed the thermophysical properties of an epoxy resin containing bisphenol-A diglyceryl ether (DGEBA) as an epoxy monomer and dicyandiamide (DICY) and diethylene triamine (DETA) as cross-linking agents. The cross-linking process occurs at the atomistic scale through the formation of bonds among the reactive particles within the epoxy and hardener molecules. To derive the interatomic coarse-grained potential for the mesoscopic model and match the density of the material studied through atomic simulations, we employed the iterative Boltzmann inversion method. The newly developed coarse-grained molecular dynamics model effectively reproduces various thermophysical properties of the DGEBA-DICY-DETA resin system. Furthermore, we simulated nanocomposites made of the considered epoxy additivated with graphene nanofillers at the mesoscopic level and verified them against continuum approaches. Our results demonstrate that a moderate amount of nanofillers (up to 2 wt.%) increases the elastic modulus and thermal conductivity of the epoxy resin while decreasing the Poisson’s ratio. For the first time, we present a coarse-grained model of DGEBA-DICY-DETA/graphene materials, which can facilitate the design and development of composites with tunable thermophysical properties for a potentially wide range of applications, e.g., automotive, aerospace, biomedical, or energy ones.