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Graphene oxide addition to epoxy still presents challenges related to attaining optimized dispersion in scale-up production. Herein, the synthesis of high-quality GO by exfoliation in ethanol enabled the spontaneous phase transfer of GO from solvent to epoxy resin to produce a masterbatch with 1.5 wt.% GO content. Nanocomposites with 0.25 wt.%, 0.50 wt.% and 0.75 wt.% nanofiller contents were obtained by masterbatch dilution in epoxy resin. The results reveal the presence of a partial cross-linked network in these nanocomposites associated with the presence of GO, even without the use of a hardener. Thermogravimetric analysis showed the influence of GO on the oxidative decomposition mechanism of epoxy resin, whose behavior was assigned to strong interactions in the GO-epoxy interphase. Furthermore, the rheological behavior changes demonstrate the high quality of the GO dispersion in the resin obtained in this work. The nanocomposites showed high viscosity increases over time and pseudoplastic behavior, which was completely different from the neat epoxy resin. Aged nanocomposites without hardener present a first chemically cross-linked layer of epoxy to GO (∼ 10% for nanocomposite at 0.50 wt.% GO content) and a supramolecular coating interacting and entangled with these structures (> 40% of epoxy chains for EP-GO50).

This work deals with the preparation of reduced graphene oxide (RGO)-TiO2 composites by a one-step hydrothermal treatment. The effect of the RGO loading on both the structural properties and photocatalytic behavior of RGO-TiO2 is deeply addressed herein. The hydrothermal treatment promoted the reduction of graphene oxide, crystallization of TiO2 into anatase, and anchoring of TiO2 nanoparticles on RGO sheets. It was observed that the prepared anatase particles showed sizes below 10 nm, whereas the RGO sheets displayed thicknesses smaller than 1 nm. The use of RGO at concentrations up to 15 wt% greatly increased the specific surface area of RGO-TiO2. It was demonstrated that the combination of RGO and TiO2 gives rise to materials with improved photocatalytic properties and tailored structural properties. The composite with the highest photoactivity was the one containing an RGO loading of 1 wt%; this composite displayed a photocatalytic rate constant about 9.5 times higher than that evaluated for pure TiO2. This behavior may be related to the stacking of RGO nanosheets when its concentration is above 1 wt%. Moreover, the addition of RGO in excess may prevent the activation of the TiO2 surface by UV light and also decrease the lifetime of the photogenerated electron-hole pairs. Therefore, it appears that 1 wt% is the optimal loading of RGO to obtain a close interfacial contact between RGO and TiO2, leading to both an effective activation of TiO2 by UV radiation and an enhanced charge transfer between RGO and TiO2. Keywords: TiO2, Reduced graphene oxide, Sol-gel process, Structural characterization, Photocatalytic evaluation

Este trabalho apresenta uma caracterização de sistemas epoxídicos a base do éter diglicidílico do bisfenol A (DGEBA), curado com dois co-monômeros do tipo amina cicloalifática - piperidina (Pip) e 4,4'-diamino-3,3'-dimetildiciclohexilmetano (3DCM) - antes e após a aplicação de irradiação com raios gama. Variações nas propriedades mecânicas e térmicas foram investigadas através de medidas do módulo elástico, da temperatura de transição vítrea e do perfil de degradação dos materiais. Foi possível observar que uma dose de irradiação de 50 kGy provoca variações sutis em propriedades como rigidez e estabilidade, que são relevantes do ponto de vista fundamental. Este trabalho permite afirmar que as variações de propriedades observadas não implicam em impacto negativo na utilização destes sistemas como biomaterial na área médica, considerando a etapa de esterilização por radiação de que são objeto.

Multi-walled carbon nanotubes (MWCNTs) functionalized with amine and carboxyl groups were used to prepare polyurethane/MWCNT nanocomposites in two distinct concentrations: a lower value of 1 mass% (spray coating) and a higher one of ~50 mass% (buckypaper based). The MWCNT-NH2 sample contained only 0.5 mass% of amine groups, whereas MWCNT-COOH contained 5 mass% of carboxyl groups. The MWCNT functionalized with low amine group content showed improved thermal properties when compared to neat thermoplastic polyurethane (TPU) and MWCNT-COOH based nanocomposites. The electrical conductivity of the polyurethane elastomer was greatly increased from 10-12 to ~10-5 S cm-1in the 1 mass% nanotube composite and to 7 S cm-1for the MWCNT-NH2 buckypaper-based nanocomposite. Furthermore, the relative high content of functional groups in the MWCNT-COOH sample, which disrupt the sp²structure in the nanotube walls, led to inferior properties; for instance the conductivity of the buckypaper based composite is one order of magnitude lower when using MWCNT-COOH in comparison with the MWCNT-NH2. These results show the range of property design possibilities available with the elastomeric polyurethane nanocomposite by tailoring the functional group content and the carbon nanotube load.

Polyurethane/multi-walled carbon nanotube (MWCNT) nanocomposites have been prepared with nanotube concentrations between 0.01 wt% and 1 wt%. MWCNT as-synthesized samples with ~74 nm diameter and ~7 μm length were introduced by solution processing in the polyurethane matrix. Scanning electron microscopy (SEM) images demonstrated good dispersion and adhesion of the CNTs to the polymeric matrix. The C=O stretching band showed evidence of perturbation of the hydrogen interaction between urethanic moieties in the nanocomposites as compared to pure TPU. Differential scanning calorimetry and positron anihilation lifetime spectroscopy measurements allowed the detection of glass transition displacement with carbon nanotube addition. Furthermore, the electrical conductivity of the nanocomposites was significantly increased with the addition of CNT.

Polímeros condutores iônicos ou eletrólitos poliméricos constituídos por um sistema de sal dissolvido em uma matriz polimérica sólida são materiais que apresentam interesse científico e potencial tecnológico. A dissolução de sais em uma matriz polimérica amorfa ou semicristalina sólida leva a estudos sobre intrigantes aspectos estruturais, que podem ser abordados por técnicas físico-químicas diversas tais como RMN, Raman e Espectroscopia de Vida Média de Pósitrons. Os estudos estruturais são correlacionados com propriedades eletroquímicas visando à utilização desses materiais em dispositivos tais como baterias, supercapacitores e células solares. Grupos brasileiros têm gradativamente ampliado os estudos e aplicações de eletrólitos poliméricos sólidos.Ionic conducting polymers or polymer electrolytes prepared with the addition of a soluble salt in a solid polymeric matrix are very important materials, associated with an intense research activity and technological efforts. Structural studies in a system of salt dissolved in an amorphous or semicrystalline solid polymeric matrix can be done with various techniques, such as NMR, Raman and Positron Annihilation Spectroscopy. The structural studies are correlated with electrochemical properties in order to evaluate these materials for applications in batteries, supercapacitors and solar cells. Brazilian researchers are contributing to the fundamental research and development of new applications of polymeric electrolytes.

Positron annihilation lifetime spectroscopy (PALS), differential scanning calorimetry, X‐ray diffraction, and polarized light optical microscopy were used to study six low molar mass poly(ethylene oxide) samples with average molar masses ranging from 1 × 103 to 10 × 103 g mol−1. Dynamic light scattering was used to determine molar mass and polydispersity rigorously. Polymer samples with 70–95% crystallinity, which is an unusual range in PALS studies, were prepared by molten material quenching. The ortho‐positronium pick‐off lifetime (τ3) and relative fractional free volume (fv), determined by the free volume model, correlated well with the average molar mass and crystallinity of the polymers. X‐ray diffraction and polarized light optical data support the interpretation of positron annihilation results. PALS parameter, I3, which is associated with high cavity content, remained approximately constant at 20–22% for all samples. The cavities are present as crystallite defects in the spherulitic open texture and the amorphous phase for the low crystallinity sample (e.g., for Mw = 1390) and at the interfaces and in interlamellar spherulite regions of the more crystalline materials. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2400–2409, 2007 [ABSTRACT FROM AUTHOR]