Extrinsic Wrinkling and Single Exfoliated Sheets of Graphene Oxide in Polymer Composites

We study the conformation of graphene oxide as the filler in nanocomposites of polystyrene and poly(methyl methacrylate) using inverse-space scattering techniques and atomic force microscopy. By subtracting the polymer scattering to estimate the scattering contribution from the graphene oxide, we discover surface fractal scattering that spans a range of more than two decades in reciprocal space, indicating that the graphene oxide within these materials is rough on a very wide range of length scales and implying extensive extrinsic wrinkling and folding. We discover that well-exfoliated, locally flat sheets of graphene oxide produce a crossover in the scattering at a length scale of 16 nm, which becomes dominated by, the signature of mass fractal scattering from thin disks or sheets. We show that the local graphene oxide structure in these polymer graphene oxide nanocomposites is identical to that of graphene oxide in a water solution studied on the same length scale. Our results confirm the presence of well exfoliated sheets that are key to achieving high interfacial areas between polymers and high aspect ratio filler in nanocomposites.