Atomistic mechanisms of adhesion and shear strength in graphene oxide-polymer interfaces

Combining experimental and computational studies of nanocomposite interfaces is highly needed to gain insight into their performance. However, there are very few literature reports, combining well-controlled atomic force microscopy experiments with molecular dynamic simulations, which explore the role of polymer chemistry and assembly on interface adhesion and shear strength. In this work, we investigate graphene oxide (GO)-polymer interfaces prevalent in nanocomposites based on a nacre-like architectures. We examine the interfacial strength resulting from van der Waals and hydrogen bonding interactions by comparing the out-of-plane separation and in-plane shear deformations of GO-polyethylene glycol (PEG) and GO-polyvinyl alcohol (PVA). The investigation reveals an overall better mechanical performance for the anhydrous GO-PVA system in both out-of-plane and in-plane deformation modes, highlighting the benefits of the donor-acceptor hydrogen bond formation present in GO-PVA. Such bond formation results in inter-chain hydrogen bond networks leading to stronger interfaces. By contrast, PEG, a hydrogen bond acceptor only, relies primarily on van der Waals inter-chain interactions, typically resulting in weaker interactions. The study also predicts that water addition increases the adhesion of GO-PEG but decreases the adhesion of GO-PVA, and slightly increases the shear strength in both systems. Furthermore, by comparing simulations and experiments, we show that the CHARMM force field has enough accuracy to capture the effect of polymer content, water distribution, and to provide quantitative guidance for achieving optimum interfacial properties. Therefore, the study demonstrates an effective methodology, in the Materials Genome spirit, toward the design of 2D materials-polymer nanocomposites system for applications demanding mechanical robustness.