Procesamiento de micro y nanofibras de polipirrol/óxido de polietileno/nylon-6 por la técnica de electrohilado**Citación estilo Chicago Olvera-Gracia, Manuel, Jorge Ricardo Aguilar-Hernández, Tetyana Kryshtab. Procesamiento de micro y nanofibras de polipirrol/óxido de polietileno/nylon-6 por la técnica de electrohilado. Ingeniería Investigación y Tecnología, XIV, 04 (2013): 575–581.Citación estilo ISO 690 Olvera-Gracia M., Aguilar-Hernández J.R., Kryshtab T. Procesamiento de micro y nanofibras de polipirrol/óxido de polietileno/ nylon-6 por la técnica de electrohilado. Ingeniería Investigación y Tecnología, volumen XIV (número 4), octubre-diciembre 2013: 575–581.

ResumenLas micro y nanofibras hechas a base de polímeros en solución pueden obtenerse usando una técnica llamada electrohilado. El principio de esta técnica se basa en la aplicación de una diferencia de potencial entre dos electrodos, uno conectado a la solución polimérica y otro al colector. Por el incremento de esta diferencia de potencial, la tensión superficial es superada y la fibra es formada depositándose sobre el plato colector. Las fibras continuas se producen en forma de una membrana. Estas fibras proveen una gran área superficial debido a su pequeño diámetro, esto hace que su aplicación comercial e interés científico sean considerados. En este estudio se han hecho fibras de una solución de polipirrol, óxido de polietileno y nylon-6. Se usaron como solventes cloroformo y ácido fórmico. Las fibras obtenidas son caracterizadas por microscopia electrónica de barrido, espectroscopia FTIR, difracción de rayos X y conductividad eléctrica. Los resultados indican que los diámetros del compósito están en un rango micro y nanométrico y la conductividad nos muestra el comportamiento de un material semiconductor.AbstractMicro and nano-fibers from polymers in solution can be easily obtained by using the so called electrospinning technique. The principle of this technique relies on applying a positive voltage to the polymer solution and a negative voltage to a collector. By increasing voltage, the surface tension will be overcome and will eject some kind of fiber deposited on the collector. The continuous fibers production will be formed like a membrane. The fibers provide a large surface area due to their small diameter, therefore, their application is considered of commercial and scientific interest. In this study, fibers from a solution made of nylon-6, polyethylene oxide and polypyrrole were obtained. Chloroform and formic acid were used as solvents for these polymers. The fibers obtained were characterized by scanning electron microscopy, FT-IR spectroscopy, X-ray diffraction and electrical conductivity. These results indicate that the diameters of the composite fibers are on the micro and nanometric range, and the conductivity thereof is that of a semiconductor material

Extinction Phenomenon in X-Ray Diffraction Technique for Texture Analysis

A method to correct pole densities (PD) for primary and secondary extinction applied for maxima of pole figures (PF) measured by X-ray diffraction, was extended to correct the whole 111 and 200 PFs for nickel samples after 75% cold rolling and subsequent annealing at 600°C during 30 minutes. The PDs were corrected, and parameters of primary and secondary extinction were calculated using the PDs obtained in PFs measured for the first order reflections with two wavelengths (Cu Kα and Co Kα - radiations) and for the second order reflections with Cu Kα – radiation. Three orientation distribution functions (ODF) were calculated, namely: the first one from 111, 200 and 220 PFs; the second one from 222 and 400 PFs (the second order reflections) and 220 PF (440 reflection is absent for the radiations used); the third one from corrected 111 and 200 PFs and not corrected 220 PF (for lack of the second order reflection). Essential differences between the obtained ODFs indicate the necessity to take into account the extinction phenomenon in analysis of textured materials. The obtained parameters of extinction were used for the evaluation of microstructure details of textured nickel depending on grains orientation that is not easily obtained by conventional metallographic methods

Photoinduced transformations of optical properties of CdSe and Ag-In-S nanocrystals embedded in the films of polyvinyl alcohol

The results of investigation of photostability of the composites of CdSe and Ag-In-S nanocrystals (NCs) embedded in the films of polyvinyl alcohol (PVA) are presented. The films were studied by photoluminescence (PL), optical absorption, micro-Raman and X-ray diffraction methods. It is found that heating of the films to 100 °C promotes PVA crystallization and stimulates an increase of the PL intensity for the NCs of both types. The latter effect is ascribed mainly to the improvement of NC surface passivation by functional groups of PVA. The illumination with the 409-nm LED’s light enhances PL intensity for CdSe NCs and decreases it for Ag-In-S NCs as well as results in the darkening of the films. The color of the Ag-In-S-PVA film restores with time, while the change of the optical properties of the CdSe-PVA composite is irreversible. The possible mechanisms of the revealed effects, such as structural transformations at NC/PVA interface as well as the formation of new light-absorbing species are discussed

Optical and structural properties of Mn 4+ activated (ZnxMg1‐x)2TiO4 red phosphors

International audienceWe report on optical and structural investigations of Mn4+ activated (ZnxMg1-x)2TiO4 red phosphors by X-ray diffraction, photoluminescence (PL) and electron paramagnetic resonance methods. The phosphors of Mg2TiO4, Zn2TiO4 and solid solutions (ZnxMg1-x)2TiO4 (x=0.25, 0.50, 0.75) with manganese content of 0.1 mol. % were synthesized at temperatures in the range of 800-1200 °C via solid state reaction. Formation of solid solutions of inverse spinel structure demonstrates the features similar to both the Mg2TiO4 and Zn2TiO4, i.e. decomposition of the (Zn,Mg)2TiO4 on the (Zn,Mg)TiO3 and MgO and separation of the secondary ZnO phase, respectively. These processes depend on the composition of solid solution and sintering temperature, and for some regimes the single phase phosphor can be obtained. The largest intensity of Mn4+ red PL is found in the Mn-doped (Zn0.25Mg0.75)2TiO4 phosphor sintered at 1100°C and it is 2 times larger than those in similar Mn4+ activated Mg2TiO4 phosphor. The differences in the PL intensity of the phosphors of solid solutions are explained by different PL thermal quenching as well as by competing processes of Mn incorporation in +2 and +4 charge states in zinc-magnesium titanate crystal lattice

Influence of Terbium Doping and Annealing on the Structural and Optical Characteristics of Sputtered Zinc Oxide Thin Films

This paper studied the structural and luminescent characteristics of undoped and doped-with-Tb3+-ions ZnO films of 200 nm and 600 nm thicknesses, grown via RF magnetron sputtering on (100) silicon substrate in Ar and Ar-O2 plasma. X-ray diffraction (XRD) patterns revealed a strong preferred orientation of ZnO and ZnO:Tb crystals of the wurtzite structure along the c-axis, perpendicular to the substrate. In the as-deposited ZnO:Tb films, the additional crystal phases, namely, Tb2O3, TbO2, and an amorphous phase, were revealed. The as-deposited undoped films were under tensile strain, that increased in the doped films. This proved the incorporation of the Tb3+ ions into the ZnO grains, and agreed with the Raman spectra investigation. The XRD data and atomic force microscopy study showed that Tb doping impeded the growth of grains and columns, respectively. The photoluminescence (PL) spectra of the doped films contained the UV band ascribed to exciton PL, a broad intrinsic defect-related band, and the narrow bands caused by the intra-shell transitions of the Tb3+ ions. Terbium doping suppressed ZnO emissions. The post-deposition rapid thermal annealing at up to 800 °C of both the undoped and doped films promoted tensile strain relaxation, grain growth, improvement in the ZnO crystal structure, and an increase in the exciton PL. The intensity of the Tb3+ PL changed non-monotonically, and was the highest for the film annealed at 600 °C. The conventional thermal annealing promoted the non-monotonic changes in the strains and grain sizes in such a way that, after annealing at 900 °C, their values became the same as in the as-deposited ZnO:Tb film. This structural change was accompanied by a decrease in the exciton and Tb3+ PL intensity. The formation of the Zn2SiO4 phase was observed via XRD, and confirmed via scanning electron microscopy. It was attributed to the interdiffusion through the film/substrate interface. The deposition in the Ar-O2 atmosphere is found to be more preferable for the formation of Tb3+ emission centers in the ZnO matrix