Uv-Vis investigations on ion beam irradiated polycarbonate

UV-VIS investigations on polycarbonate irradiated with accelerated U ions are reported. The experimental data are consistent with the decrease of the energy gap due to irradiation and indicate the formation of isolated conjugated structures. The relatively weak decrease of the energy gap and the shape of the electron spin resonance lines indicate that the conjugated structures are isolated within the polymeric matrix. published: 8 November, 2008

Raman investigations of the radiation-induced modifications in iPP-VGCNF nanocomposites: The nanofillers’ tale

Nanocomposites of isotactic polypropylene loaded by various amounts of vapor-grown carbon nanotubes ranging from 0 to 20% wt. were obtained by extrusion. Raman investigations on these nanocomposites are reported. The nanocomposites were irradiated using a 60Co, with an integral dose of 1 kGy/h up to integral doses of 9 kGy, 18 kGy, and 27 kGy, in air, at room temperature. Raman measurements were performed by using a Bruker Senterra confocal Raman spectrometer operating at 785 nm. The research is focused on the information contained within the D and G Raman lines of these nanocomposites as a function of nanotube loading for various integral doses. The experimental data revealed the graduate silencing of the molecular motions assigned to the polymeric matrix due to the nanofiller and ionizing radiation. Based on experimental data, it is concluded that the positions of the D and G lines exhibit faint shifts due to the irradiation and that (on average) these shifts are consistent with the changes of the positions of D and G lines upon the increase of the loading with vapor-grown carbon nanofibers. Raman data suggest that the irradiation relaxes the pressure exerted on the nanofiller by the polymeric matrix, indicating a path to improve the physical features of polymer-carbon nanostructure nanocomposites. The research demonstrates the capability of Raman spectroscopy to sense the modifications of molecular vibrations in polymer-based nanocomposites, for both the polymeric matrix and the nanofiller

Polyethylene oxide—fullerene nanocomposites

Polyethylene oxide – fullerene nanocomposites have been prepared by using the solution path with water as solvent (only for the polymer). The dispersion of C60 within the polymer solution was achieved by high power sonication. The study aims to a better understanding on the effect of C60 nanoparticles on the macromolecular chains. Raman Wide Angle X Ray spectroscopy, Differential Scanning Calorimetry, and Thermogravimetric Analysis were used to inspect the interactions between the nanofiller and macromolecular chains. The experimental results revealed a completely different behavior of fullerene dispersed within polymeric matrices than using carbon nanotubes or nanofibers as nanofiller. The observed behavior was explained by the low aspect ratio of C60 compared to nanotubes and by the low thermal conductivity of C60 compared to the thermal conductivity of others carbon nanostructures

Spectroscopic investigations on PVDF-Fe2O3 nanocomposites

Polyvinylidene fluoride-iron oxide (PVDF-Fe2O3) nanocomposites have been obtained my melt mixing of PVDF with Fe2O3 nanoparticles. The interactions between the polymeric matrix and the nanofiller have been investigated by wide angle X-ray scattering (WAXS), Fourier transform infrared spectroscopy (FTIR), and Raman spectroscopy, using both red and green excitations (lasers). WAXS, FTIR, and Raman spectra confirm that all samples contain α PVDF as the major crystalline form of the polymeric matrix. Experimental data revealed small changes in the positions of X-ray lines as well as modifications of the width of X-ray lines upon loading by Fe2O3 nanoparticles. FTIR and Raman spectra are dominated by the lines of the polymeric matrix. Within the experimental errors, the positions of Raman lines are not affected by the wavelength of the incoming electromagnetic radiation, although they are sensitive to the strain of the polymeric matrix induced by addition of the nanofiller. The loading of the polymeric matrix with nanoparticles stretches the macromolecular chains, affecting their vibrational spectra (FTIR and Raman). A complex dependence of the positions of some Raman and FTIR lines on the loading with Fe2O3 is reported. The manuscript provides a detailed analysis of the effects of nanofiller on the position of WAXS, FTIR, and Raman lines

Adding Autonomic Healing Capabilities to Polyethylene Oxide

The addition of autonomic healing (frequently defined as self-healing) capabilities to a water-soluble polymer (polyethylene oxide, PEO) is for the first time reported. The self-healing system consists of urea-formaldehyde microcapsules filled with dicyclopentadiene and first-generation Grubbs catalyst, dispersed within polyethylene oxide. Raman spectroscopy, optical microscopy, electron microscopy, and thermogravimetric analysis were used to characterize this autonomic healing system. Self-healing capabilities were confirmed by mechanical testing (load–displacement, engineering stress–engineering strain, and true stress–true strain dependences) recorded at very slow elongation rates (0.01 mm/s). The testing fate was chosen to allow for the complete consumption of the monomer before fracture (the polymerization kinetics of PEO was estimated from Raman measurements)

On orientation memory in high density polyethylene - Carbon nanofibers composites

An orientation memory effect in high density polyethylene (HDPE) filled with vapor grown carbon nanofibers (VGCNF) is reported. Two-dimensional X-ray (2DXR) confirmed the reorientation of HDPE crystallites upon the uniaxial stretching of HDPE and HDPE filled by VGCNFs. This anisotropy of 2DXR spectra was decreased by heating all stretched samples (loaded or not loaded by VGCNFs) from room to the melting temperature of HDPE. Upon cooling these samples to room temperature, it was noticed that only the nanocomposite retained a weak partial (uniaxial) order, while HDPE showed a completely isotropic 2DXR spectrum. It was concluded that during the stretching of nanocomposites the crystallites and VGCNFs were aligned along the uniaxial stress. Upon heating, the crystalline phase was melted, while the orientation of the VGCNFs was not significantly disturbed. The recrystallization of the polymer started preferentially from the VGCNF - polymer interphase, resulting into an anisotropic crystalline structure

On the thermogravimetric analysis of polymers: Polyethylene oxide powder and nanofibers

Thermogravimetric analysis of polyethylene oxide (powder and nanofibers obtained by force spinning water or chloroform solutions of polyethylene oxide) was studied using different theoretical models such as Friedman and Flynn-Wall-Ozawa. A semiempirical approach for estimating the “sigmoid activation energy” from the thermal degradation was suggested and confirmed by the experimental data on PEO powder and nanofibers\u27 mats. The equation allowed for calculating a “sigmoid activation energy” from a single thermogram using a single heating rate without requiring any model for the actual complex set of chemical reactions involved in the thermal degradation process. For PEO (powder and nanofibers obtained from water solutions), the “sigmoid activation energy” increased as the heating rate was increased. The sigmoid activation energy for PEO mats obtained from chloroform solutions exhibited a small decrease as the heating rate was increased. Thermograms\u27 derivatives were fitted to determine the coordinates of the inflection points. The “sigmoid activation energy” was compared to the activation energy determined from the Flynn-Wall-Ozawa model. Similarities between the thermal degradation of polyethylene oxide powder and of the nanofibers obtained from water solutions were discussed. Significant differences between the sigmoid activation energies of the mats obtained from water and chloroform solutions were reported

Raman Spectroscopy of Carbonaceous Materials: A Concise Review

A critical review focused on the Raman spectroscopy of carbonaceous materials and of polymer-based nanocomposites that contain carbonaceous (nano) materials as fillers is presented. The origin, assignment, and parameters (position, intensity, area, width, and shape) of main Raman modes (radial breathing mode, D-mode, G-mode, G\u27-mode, and so forth) as well as the effect of the interactions of carbonaceous materials on the parameters of these modes is briefly discussed. The effect of dopants and of polymeric matrices on the parameters of Raman bands is succinctly analyzed. The review will provide the basic and most elementary knowledge required to understand and discuss the Raman spectra of carbonaceous materials

Self-healing of high elasticity block copolymers

A new route for adding self-healing properties to soluble polymers is presented briefly. Self-healing block copolymers (polystyrene-block-polybutadiene block-polystyrene from Sigma-Aldrich) were obtained by dissolving the polymer in a solvent that neither dissolves the microbubbles nor deactivate the Grubbs catalyst. The self-healing block copolymer has been obtained by mixing the polymer, the solvent, the microbubbles filled with monomer (dicyclopentadiene), and the Grubbs\u27 catalyst followed by the evaporation of the solvent. The structure of self-healed high elasticity block copolymer has been investigated by optical and Scanning Electron Microscopy. Raman spectroscopy and mechanical data suggested that the block copolymer exhibits self-healing features

On a novel approach to the thermogravimetric analysis of polymers: Polystyrene

A novel equation that describes the temperature dependence of the residual mass fraction (as determined by thermogravimetric analysis) is derived, assuming that the dependence of the residual mass fraction on temperature has a sigmoidal shape. The equation allows the estimation of the sigmoidal activation energy solely from the experimental data at a single heating rate. The consistency with the isoconversional approach and the relationship between the Ozawa and sigmoidal activation energies are reported. The equation was successfully tested by the thermal degradation of atactic polystyrene at various heating rates. Both the thermograms and their derivatives are analyzed in detail