Diversity of Nanofibers from Electrospinning: from Graphitic Carbons to Ternary Oxides.

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Detection of Moisture and Methanol Gas Using a Single Electrospun Tin Oxide Nanofiber

This letter reports the fabrication of a gas sensor based on a single tin oxide nanofiber made from dimethyldineodecanoate tin using electrospinning and metallorganics decomposition techniques. The fabricated sensor has been used to detect moisture and methanol gas. It showed high sensitivity to both gases and the response times of the complete testing system are in the range of 108–150 s for moisture, and 10–38 s for methanol gas, respectively

Optical Bandgap and Photoconductance of Electrospun Tin Oxide Nanofibers

Optical and photoconductive properties of transparent SnO2 nanofibers, made from C22H44O4Sn via electrospinning and metallorganic decomposition, were investigated using Fourier transform infrared and ultraviolet (UV)/visible spectrometry and the two-probe method. Their optical bandgap was determined from their UV absorption edge to be 3.95–4.08 eV. Their conductance responds strongly to UV light for a wavelength of 254 nm: in air its steady-state on-to-off ratios are 1.31–1.56 (rise) and 1.25–1.33 (fall); its 90% rise and fall times are 76–96 and 71–111 s, respectively. In a vacuum of about 10−4 torr, its on-to-off ratios are higher than 35.6 (rise) and 3.4 (fall), respectively, and its 90% rise and fall times are longer than 3×104 s

Pyrolysis Temperature and Time Dependence of Electrical Conductivity Evolution for Electrostatically Generated Carbon Nanofibers

Carbon nanofibers were produced from polyacrylonitrile/N, N-Dimethyl Formamide (PAN/DMF) precursor solution using electrospinning and vacuum pyrolysis at temperatures from 773-1273 K for 0.5, 2, and 5 h, respectively. Their conductance was determined from I – V curves. The length and cross-section area of the nanofibers were evaluated using optical microscope and scanning probe microscopes, respectively, and were used for their electrical conductivity calculation. It was found that the conductivity increases sharply with the pyrolysis temperature, and increases considerably with pyrolysis time at the lower pyrolysis temperatures of 873, 973, and 1073 K, but varies, less obviously, with pyrolysis time at the higher pyrolysis temperatures of 1173 and 1273 K. This dependence was attributed to the thermally activated transformation of disordered to graphitic carbons

Temperature dependent charge transport mechanisms in carbon sphere/polymer composites

Carbon spheres (CS) with diameters in the range $2 - 10 \mu m$ were prepared via hydrolysis of a sucrose solution at $200^o C,$ and later annealed in $N_2$ at $800^o C.$ The spheres were highly conducting but difficult to process into thin films or pressed pellets. In our previous work, composite samples of CS and the insulating polymer polyethylene oxide (PEO) were prepared and their charge transport was analyzed in the temperature range $80 K < T < 300 K.$ Here, we analyze charge transport in CS coated with a thin polyaniline (PANi) film doped with hydrochloric acid (HCl), in the same temperature range. The goal is to study charge transport in the CS using a conducting polymer (PANi) as a binder and compare with that occurring at CS/PEO. A conductivity maxima was observed in the CS/PEO composite but was absent in CS/PANi. Our data analysis shows that variable range hopping of electrons between polymeric chains in PANi-filled gaps between CS takes on a predominant part in transport through CS/PANi composites, whereas in CS/PEO composites, electrons travel through gaps between CS solely by means of direct tunneling. This difference in transport mechanisms results in different temperature dependences of the conductivity.Comment: 7 pages, 6 figure

Electronic Transport Properties of Incipient Graphitic Domains Formation in PAN Derived Carbon Nanofibers

The carbon nanofibers used in this work were derived from a polyacrylonitrile (PAN)/N, N-dimethyl formamide (DMF) precursor solution using electrospinning and vacuum pyrolysis techniques. Their conductivity, σ, was measured at temperatures between 1.9 and 300 K and transverse magnetic field between -9 and 9 T. Zero magnetic field conductivity σ(0,T) was found to increase monotonically with the temperature with a convex σ(0,T) versus T curve. Conductivity increases with the external transverse magnetic field, revealing a negative magnetoresistance at temperatures between 1.9 and 10 K, with a maximum magnetoresistance of - 75 % at 1.9 K and 9 T. The magnetic field dependence of the conductivity and the temperature dependence of the zero-field conductivity are best described using the two-dimensional weak localization effect

Cumplimiento y efectividad de las normas, del Código de Familia, referente a la protección integral de los adultos mayores en el departamento de Usultán, 2001-2002

Evaluar el cumplimiento y grado de efectividad de las normas plasmadas en la Constitución de la República, Código de Familia, tratados, convenciones y derechos, en los cuales el Estado se obliga a brindar una asistencia integral a la población de adultos mayores. La presente investigación permitirá en la medida que se aplique la metodología adecuada, una serie de predicciones incipientes, que serán punto de partida para investigaciones más acertadas acerca del fenómeno en investigación, todo ello obtenido mediante un método Descriptivo, por encuesta como núcleo del proceso, pues habilitará obtener respuestas de las unidades de análisis, como son los adultos mayores, que nos llevarán a la comprobación de hipótesis y al cumplimiento de los objetivos planteados. Apoyándose el proceso de investigación, por medio de un análisis documental, o sea un análisis de teorías fundamentales, para el mayor grado de comprensión de los resultados de la investigación de campo. Todo lo anterior, respaldado por parámetros de una investigación científica, que lleva consigo un proceso sistemático, lo que conducirá a la realidad; y a la vez se utilizará un método de análisis de resultados deductivo-inductivo, lo que facilitará deducir de primicias generales, razonamientos lógicos y de juicios particulares, a conclusiones generales. Asi se concluye que Como podemos deducir la tendencia demográfica de nuestro país, a aumentar la taza poblacional de adultos mayores, se hará presente nuevamente al final del primer decenio del siglo, considerando por ello, que si la población actual es de 451,705, para el año 2,010 será de 602,367, y estimamos que para el año 2,025 ésta ascenderá aproximadamente a 990,000 adultos mayores. De acuerdo a los porcentajes vertidos por las instituciones ISSS e INPEP, de afiliación de adultos mayores, determinamos que la población amparada bajo estas instituciones es de 24.98%, siendo el 75.02% el número de adultos mayores, que no gozan de ningún tipo de pensión, y por lo tanto tampoco son acogidos por los programas de atención que brindan estas institucione

Tin oxide micro/nano fibers from electrostatic deposition

SnO2 micro/nano fibers in the rutile structure were synthesized using electrospinning and metallorganic decomposition techniques. Fibers were electrospun using two different precursor solutions, one based on SnCl4 and the other on C22H44O4Sn. The fibers were sintered in air for two hours at 400, 500, 600, 700 and 800ºC. SEM, AFM, XRD, XPS and Raman microspectrometry were used to characterize the sintered fibers. The results showed that the fibers were composed of SnO2 and that the SnCl4 precursor led to better results in terms of uniformity/continuity of the fibers