In this study, films of graphene oxide and chemically or thermally reduced graphene oxide were produced by a simple vacuum filtration method and submitted to a thorough characterization by X-ray diffraction (XRD), Raman and infrared spectroscopies, field-emission scanning electron microscopy, transmission electron microscopy, atomic force microscopy, confocal microscopy, and contact angle measurements. Graphene oxide (GO) was produced from graphite by the modified Hummers method and thereafter reduced with NaBH₄ or by heating under argon in a tubular furnace. The films were produced from aqueous solutions by vacuum filtration on a cellulose membrane. Graphite presents two characteristic XRD peaks corresponding to d=0.34nm and d=0.17nm. After oxidation, only a peak at d=0.84nm is found for powder GO, confirming the insertion of oxygen groups with an increase in the interplanar distance of graphene nanoplatelets. However, for GO films, other unexpected peaks are observed at d=0.63nm, d=0.52nm, and d=0.48nm. After reduction, both chemical and thermal, the peak at 0.84 nm disappears, while those corresponding to interplanar distances of 0.63 nm, 0.52 nm, and 0.48 nm are still present. The other characterizations confirm the production and chemical composition of GO and reduced GO films. The results indicate the combination of crystalline regions with different interplanar distances, suggesting the ordering of graphene/graphene oxide intercalated sheets.

In this work, a varied amount of acetone was employed to dissolve an epoxy resin and then a route was followed to remove the acetone, simulating a frequently used method to disperse nanofillers in thermoset matrices. Analyses were then carried out to address the influence of residual acetone on the curing process and on the epoxy properties. The results showed a detrimental effect on the mechanical properties of the cured epoxy due to the presence of residual acetone and also a less brittle-like fracture of the specimen. Fourier transform infrared spectroscopy and thermogravimetric analyses were additionally used to characterize the cured resins and have also indicated the presence of a small amount of acetone. Nevertheless, rheological measurements indicated that 10.0 wt.% acetone addition on the resin causes a significant decrease in viscosity (around 50%) which may promote a better dispersion of nanofillers.

The authors employed the equilibrium molecular dynamics technique to calculate the self-diffusion coefficient and the shear viscosity for simple fluids that obey the Lennard-Jones 6-12 potential in order to investigate the validity of the Stokes-Einstein (SE) relation for pure simple fluids. They performed calculations in a broad range of density and temperature in order to test the SE relation. The main goal of this work is to exactly calculate the constant, here denominated by α, present in the SE relation. Also, a modified SE relation where a fluid density is raised to a power in the usual expression is compared to the classical expression. According to the authors’ simulations slip boundary conditions (α=4) can be satisfied in some state points. An intermediate value of α=5 was found in some regions of the phase diagram confirming the mode coupling theory. In addition depending on the phase diagram point and the definition of hydrodynamics radius, stick boundary condition (α=6) can be reproduced. The authors investigated the role of the hydrodynamic radius in the SE relation using three different definitions. The authors also present calculations for α in a hard-sphere system showing that the slip boundary conditions hold at very high density. They discuss possible explanations for their results and the role of the hydrodynamic radius for different definitions in the SE relation.

In this work, nanocomposites were prepared by adding a small amount of single walled carbon nanotubes (SWCNTs) to an epoxy resin aiming to study the resulting mechanical, viscoelastic and thermal properties of the nanocomposites. To optimize the processing of the nanocomposites and to favor a homogeneous dispersion of the SWCNTs on the matrix, acetone was used to reduce resin viscosity, increasing diffusion of the SWCNTs in the solution. The epoxy/SWCNTs/acetone systems were also sonicated in order to minimize entanglement of the SWCNTs. The systems were characterized by Fourier transform infrared spectroscopy, Raman spectroscopy, thermogravimetry, differential scanning calorimetry and dynamic mechanical analysis. The results indicated that the addition of small amounts of SWCNTs to epoxy leads to slight structural changes in the epoxy matrix which, together with the presence of SWCNTs, may reflect on its mechanical and viscoelastic propertie