Extrinsic Wrinkling and Single Exfoliated Sheets of Graphene Oxide in Polymer Composites
Chemistry of Materials, 2016 OPEN ACCESS
Graphene oxide, a functionalized form of graphene, is among the most commonly used graphenes for thermoplastic composites, due to its ease of processing and availability in large quantities. However, graphene oxide is a flexible material known to change conformation and contort when in solution. This poses the question what is happening within polymer composites? However, studying the conformation of a carbon material which is embedded in a solid, largely carbon matrix is not trivial. Here we achieve this and demonstrate that the local structures of graphene oxide within a polymer are identical to those in water.
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.
Distortion of Chain Conformation and Reduced Entanglement in Polymer–Graphene Oxide Nanocomposites
ACS Macro Letters, 2016, OPEN ACCESS
When graphene oxide is loaded in to thermoplastic polymers it is expected that the polymer chains range of motion will be confined by the presence of the large flat graphene oxide sheets. Here we quantify this effect demonstrating a decrease in the number on entanglments between polymer chains, which then translates into a change in the bulk polymer's melt rheology. This increases our understanding into how the local behavior between poylmer chains and 2D particles effects the bulk properties important to the processing of thermoplastics.
We study the conformations of polymer chains in polymer–graphene oxide nanocomposites. We show that the chains have a reduced radius of gyration that is consistent with confinement at a solid interface in the melt, as is expected for well-dispersed, high aspect ratio nanoparticles that are much larger than the polymer coil size. We show that confinement of the polymer chains causes a corresponding reduction in interchain entanglements, and we calculate a contribution to the plateau modulus from the distorted polymer network via a simple scaling argument. Our results are a significant step forward in understanding how two-dimensional nanoparticles affect global material properties at low loadings.
ACS Macro Lett., 2016, 5, pp 430–434