Individual graphene oxide platelets through direct molecular exfoliation with globular amphiphilic hyperbranched polymers

In this study, we used a solution process, involving direct molecular exfoliation of graphite oxide (GO) stacked layers, to obtain individual graphene oxide platelets (GOPs) through amphiphilic hyperbranched polymers (HPs). The HPs, based on poly(amic acid) and polyimide with terminal amino functionalities, were obtained through a facile "A(2) + B-3" synthesis; gel permeation chromatography of the HPs revealed molecular weights of 5000-8200 g mol(-1) with a distribution of polydispersity between 2.0 and 4.2. Next, we inserted these globular HPs into the interlayer spaces of GO to prepare a series of GO/HP nanohybrids possessing intercalated and exfoliated morphologies. The intercalation processes featured a critical transition point at which a dramatic enlargement occurred to the interlayer spacing, depending on the content of the bulky embedded HPs. From transmission electron microscopy images, we observed transparent folding of the GOPs; powder X-ray diffraction analysis revealed individual nanosheets with well-defined diffraction patterns. Incorporating the bulky three-dimensional globular structure into the layered GO significantly influenced the solution exfoliation, allowing us to examine the intercalating behavior of GO intergallery. This solution-phase methodology, through direct HP molecular exfoliation, provides the way toward obtaining individual nanosheets, opening up opportunities for platelet-like nanographene oxide materials in many technological applications.