Suchergebnisse

Bulk-modified ultra-high molecular weight polyethylene (UHMWPE) is a biomaterial currently used for joint replacements. As an alternative, we assess the frictional behaviour of coatings based on graphene/UHMWPE composites and sprayed graphene, which maintain the high performance of the UHMWPE matrix. Composite coatings were prepared with 0–4.6 wt% of graphene nanoplatelets (GNP) and 1–2 layered graphene (2LG). Mechanical properties of the coatings were measured by nanoidentation and friction coefficients were determined with a ball-on-disk tribometer. The results indicate that GNP present better tribological behaviour than 2LG. Spray-coated GNP shows the lowest friction, 40% less than UHMWPE, although with low adhesion. An increase of 10% in elastic modulus and 30% in hardness was measured for composite coatings with 2–5 wt% graphene. ; Special thanks are directed to the Analysis Service of Instituto de Carboquímica, ICB-CSIC, in particular to M.D. Domínguez, N. Fernández and I. Fernández. This work has been funde(2016–79282-d by MINECO and European Regional Development Fund C5-1ENE -R), and Government of Aragon and European Social Fund (DGA-ESF-T66 "Grupo Consolidado"). ; Peer reviewed

© 2017. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/ ; Polyvinylidene fluoride (PVDF)/single-walled carbon nanotube (SWCNT) composites are characterized by X-ray diffraction and scanning calorimetry, and studied by dielectric relaxation spectroscopy (DRS) in the temperature range of −75 to 150 °C. The effects of SWCNTs and SWCNT functionalization are analyzed in terms of α and αc relaxation, dielectric permittivity, loss tangent, and AC electrical conductivity. Some small changes are detected in α relaxation with the addition of SWCNTs, and a strong influence of SWCNTs is observed in the other relaxation αc. Below the percolation threshold, the dielectric permittivity of functionalized SWCNT composites increases compared to blank PVDF, without notable changes in the dielectric loss. All the composite systems show an electrical percolation behavior with different thresholds depending on SWCNT functionalization. Threshold concentrations remain nearly unchanged in the whole temperature and frequency ranges. The base PVDF conductivity strongly depends on temperature and frequency, while the maximum conductivity above the percolation remains nearly unchanged (∼10−2 S/m) for all the systems, temperatures and frequencies. ; Special thanks are directed to the Analysis Service of Instituto de Carboquímica, ICB-CSIC, in particular to I. Fernández. This work has been funded by MINECO and European Regional Development Fund (ENE-2016-79282-C5-1-R), and Government of Aragon and European Social Fund (DGA-T50 and DGA-ESF-T66 "Grupos Consolidados"). ; Peer reviewed

Poly(methyl methacrylate) (PMMA) composites containing raw or purified single-walled carbon nanotubes (SWCNTs) are prepared by in-situ polymerization and solution processing. The SWCNTs are purified by centrifugation in a Pluronic surfactant, which consists of polyethyleneoxide and polypropyleneoxide blocks. Both the effects of SWCNT purity and non-covalent functionalization with Pluronic are evaluated. Electrical conductivity of PMMA increases by 7 orders of magnitude upon the integration of raw or purified SWCNTs. The best electrical properties are measured for composites made of purified SWCNTs and prepared by in-situ polymerization. Strains at fracture of the SWCNT/PMMA composites are nearly identical to those of the neat matrix. A certain decrease in the work to fracture is measured, particularly for composites containing purified SWCNTs (-31.6 %). Fractography and Raman maps indicate that SWCNT dispersion in the PMMA matrix improves upon the direct addition of Pluronic, while dispersion becomes more difficult in the case of purified SWCNTs. ; This work was funded by the Spanish MINECO under the projects TEC2010-15736, MAT2010-16175 (CICYT), CTQ2006-02330 and PRI-PIBAR-2011-1, and the Government of Aragon (DGA) and the European Social Fund (ESF) under Project DGA-ESF-T66 CNN. C. Ruano acknowledges MINECO for her PhD grant BES2007-17250. ; Peer reviewed

9 pages, 9 figures.-- Available online 21 February 2014 ; The effect of -irradiation on the structure and composition of chemically synthesized few-layered graphene materials was studied. Fully oxidized graphene oxide and graphene nanoribbons, as well as their respective chemically post-reduced forms, were treated under -irradiation in an air-sealed environment. Three different irradiation doses of 60, 90 and 150 kGy were applied. Structure and composition of the irradiated materials were analyzed by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), Raman spectroscopy and Xray photoelectron spectroscopy (XPS). The XRD patterns were not affected by - irradiation, and small changes were observed in the FTIR and TGA results. However, significant modifications were detected by Raman spectroscopy and XPS, particularly in the Raman G/D band intensity ratios and in the C 1s XPS profiles. Comparatively, the changes in Raman and XPS spectra after -irradiation were even greater than those occurring during the chemical reduction of graphene oxides. Our results indicate that the graphene carbon lattice was strongly affected by -irradiation, but the materials experienced small variations in their oxygen content. ; This work was funded by the Spanish MINECO under the projects TEC2010-15736, MAT2010-15026, MAT2010-16175 (CICYT) and PRI-PIBAR-2011-1, CSIC under Project 201080E124 and the Government of Aragon (DGA) and the European Social Fund (ESF) under Project DGA-ESF-T66 CNN. ; Peer reviewed