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Item High-Tribological-Performance Polymer Nanocomposites: An Approach Based on the Superlubricity State of the Graphene Oxide Agglomerates(MDPI) Ferreira, Eder Henrique Coelho; Vieira, Angela Aparecida; Vieira, Lucia; Fechine, Guilhermino José MacêdoHere, nanocomposites of high-molecular-weight polyethylene (HMWPE) and HMWPE- UHMWPE (80/20 wt.%) containing a low amount of multilayer graphene oxide (mGO) (≤0.1 wt.%) were produced via twin-screw extrusion to produce materials with a higher tribological performance than UHMWPE. Due to the high viscosity of both polymers, the nanocomposites presented a signifi- cant concentration of agglomerates. However, the mechanical (tensile) and tribological (volumetric loss) performances of the nanocomposites were superior to those of UHMWPE. The morphology of the nanocomposites was investigated using differential scanning calorimetry (DSC), microtomogra- phy, and transmission electron microscopy (TEM). The explanation for these results is based on the superlubricity phenomenon of mGO agglomerates. It was also shown that the well-exfoliated mGO also contained in the nanocomposite was of fundamental importance as a mechanical reinforcement for the polymer. Even with a high concentration of agglomerates, the nanocomposites displayed tribological properties superior to UHMWPE’s (wear resistance up to 27% higher and friction co- efficient up to 57% lower). Therefore, this manuscript brings a new exception to the rule, showing that agglomerates can act in a beneficial way to the mechanical properties of polymers, as long as the superlubricity phenomenon is present in the agglomerates contained in the polymer.Item In-situ transmission electron microscopy (TEM) investigation of the reduction process in graphene oxide(Springer Nature Link) Silva, Douglas Soares da; Viana, Gustavo Alexandre; Silva Filho, José Maria Clemente da; Kretly, Luiz Carlos; Chaves Neto, Antônio Maia de Jesus; Vieira, Lúcia; Barros, Tárcio André dos Santos; Marques, Francisco das ChagasThe reduction processes of graphene oxide (GO) aim to remove functional groups such as H2O, CO, and CO2 to promote the properties of GO towards those of pure graphene. We adopted the thermal reduction process from room temperature to 320 °C. The transmission electron microscopy (TEM) technique was used to probe the effect of reduction mechanisms. It was observed that the plasmon peaks, referring to sp2 carbon bonds in crystalline structures, are more evident in the reduced graphene oxide (rGO) than GO. The fine structure at the K edge of carbon shows differences in shape linked to the density of states above the Fermi level. Electron energy loss spectroscopy (EELS) analyses revealed an increase in the fraction of sp3 bonds in the reduced sample, consistent with the reduction of functional radicals in the GO structure.