Resumen Se obtuvieron fibras puras de poliacrilonitrilo con un diámetro a escala micrométrica y se colectaron radialmente mediante un sistema de hilatura húmeda por inmersión. Como polímero precursor se utilizó polvo de poliacrilonitrilo de alta pureza. Este método es rápido y sencillo para fabricar fibras de PAN micrométricas. El diámetro de la fibra puede controlarse fácilmente ajustando el tamaño de la hilera. Las microfibras de PAN uniformes, lisas y continuas se modificaron adecuadamente mediante estabilización térmica e hidrólisis alcalina para obtener fibras sensibles al pH. Se investigó el efecto del tamaño del diámetro de la fibra en el comportamiento de actuación química en términos de características de cambio de longitud bajo la influencia del pH de las soluciones. Las microfibras mostraron un comportamiento de expansión/contracción y generación de fuerza estimulado por cambios en el pH de 1-14. Mediante microscopía electrónica de barrido se pudo corroborar la formación de fibras PAN con diámetros en escala micrométrica de 91-287 µm. La espectroscopia FT-IR reveló que los grupos nitrilo (C≡N) del PAN se convirtieron en grupos carboxílicos (COOH), los cuales son necesarios para proporcionar la deformación de las microfibras gelificadas de PAN.

Abstract Pure polyacrylonitrile fibers with diameter size at micrometric scale were obtained and collected radially using an immersion-jet wet spinning system. High purity polyacrylonitrile powder was used as precursor polymer. This method is a fast and easy approach to fabricate micrometric PAN fibers. Fiber diameter can be easily controlled by adjusting the size of the spinneret. Uniform, smooth and continuous PAN microfibers were suitable modified by thermal stabilization and alkaline hydrolysis to obtain pH-sensitive fibers. The effect of diameter size fiber on the chemical actuation behavior was investigated in terms of length change characteristics under the influence of pH solutions. The microfibers showed expanding/contracting behavior and force generation stimulated by changes in pH from 1-14. By means of scanning electron microscopy, the formation of PAN fibers with diameters on the micrometer scale of 91-287 µm could be corroborated. FT-IR spectroscopy revealed that the nitrile (C≡N) groups of PAN were converted to carboxylic groups (COOH), which are necessary to provide the deformation of the PAN gel microfibers.

Rare earths (Europium, cerium)-doped CdS nanofilms are prepared using the growth technique chemical bath deposition (CBD) at the reservoir temperature of 70±2°C varying the synthesis time in a wide range. For the rare earths doped CdS nanofilms the synthesis time was ranged from 80 to 135 min. The rare earths molar concentration was in the range 0.0≤x≤3.47, which was determined by energy dispersive X-ray spectroscopy (EDS). The X-ray diffraction (XRD) analysis reveals that CdS nanofilms showed the zinc blende (ZB) crystalline phase. The nanocrystal size was ranged from 2.67 to 2.35 nm for the CdS and 1.84-2.33 nm for rare earth-doped CdS that were determined by the Debye-Scherrer equation from ZB (111) direction and it was confirmed by transmission electron microscopy (TEM). The doped CdS exhibits a direct band gap that diminishes with the increase of the synthesis time, from 2.50 to 2.42 eV, which was obtained by transmittance. The room-temperature photoluminescence of CdS presents the band-to-band transition at 431 nm, which is associated with quantum confinement because the grain size is less than its Bohr exciton radius and a dominant band at 523 nm, which is called the optical signature of interstitial oxygen. Eu3+-doped CdS photoluminescence shows the dominant radiative peak at 576 nm that is associated to the intra-4f radiative transition of Eu3+ ions, which corresponds to the magnetic dipole transition, (5D0→7F1). For the Ce3+-doped CdS the dominant radiative transitions are clearly redshifted. Additionally, other radiative peaks associated at structural defects are observed. The passivation of the CdS by rare earths was approximately of two orders of magnitude obtaining better results with cerium.

This work presents the characterization of ZnTe nanolayers grown on GaAs and GaSb (100) substrates by the Atomic Layer Deposition (ALD) regime. Under certain conditions, the alternating exposition of a substrate surface to the element vapours makes possible the growth of atomic layers in a reactor where the atmosphere is high-purity hydrogen. ZnTe was grown simultaneously on GaAs and GaSb at the same run, allowing, a comparison between the effects produced by the superficial processes due to the different used substrates, thereby eliminating possible unintended changes of growth parameters. Nanolayers on GaSb maintained their shiny appearance even at temperatures near 420°C. It was found that for exposure times below 2.5 s there was not growth on GaAs, while for GaSb the shortest time was 1.5 s at 385°C. By HRXRD the peak corresponding to (004) diffraction plane of ZnTe was identified and investigated, the FWHM resulted very wide (600-800 arcsec) indicating a highly distorted lattice mainly due to mosaicity. Raman scattering shows the peak corresponding to LO-ZnTe, which is weak and slightly shifted in comparison with the reported for the bulk ZnTe at 210 cm-1. Additionally, the measurements suggest that the crystalline quality have a dependence with the growth temperature.

In this work reports results related to growth and characterization of AlxGa1-xAs epilayers, which were grown in a metallic-arsenic-based-MOCVD system. The gallium and aluminium used precursors were trimethylgallium (TMGa) and trimethylaluminium (TMAl), respectively. By photoluminescence measurements observed, that only samples grown at temperatures above 800°C display photoluminescence. Hall measurements on the samples showed highly compensated material. Samples grown at temperatures lower than 750°C were highly resistive. Independently of the V/III ratio; the samples grown at higher temperatures were n-type. As the temperature is increased the layer compensation decreases. The AlxGa1-xAs epilayers resulted n-type with an electron concentration of 1×1017 cm-3 and a corresponding carrier mobility of ~2200 cm2/V×s. Raman spectra show vibrational bands associated to TO-GaAs-like (262 cm−1), LO-GaAs-like (275 cm-1), TO-AlAs-like (369 cm-1) and LO-AlAs-like (377 cm-1). The Raman spectra show the epilayers become more defective as the growth temperature is increased. The chemical composition was studied by SIMS exhibit the presence of silicon, carbon and oxygen as main residual impurities. The silicon concentration of ~1.0×1017 cm-3 is very close to the carrier concentration determined by the van der Pauw measurements. The residual oxygen detected on the samples maybe responsible of the weak photoluminescence signal of the AlxGa1-xAs layers.

Whey is produced during cheese manufacture, some of its constituents are lactose and proteins. In different countries such constituents are separated for use as raw material; some of the processes to separate these components are by ultra and nano-filtration, however most common methods for the determination of lactose and proteins are not accurate. This paper shows that infrared spectroscopy is a good alternative for the quantification of lactose and proteins after ultra- and nano-filtration processes. Linear calibration curves were obtained with this analytical technique for aqueous solutions containing lactose or protein in the range 0 to 20%; after 20% lactose, the solution becomes saturated. Infrared spectroscopy is a rapid and precise method that could be successfully used to quantify these compounds and follow the ultra- and nano-filtration process applied to purify lactose and proteins from whey.

El suero se produce durante la elaboración de queso, algunos de sus componentes son lactosa y proteínas. En diferentes países estos constituyentes son separados para usarse como materias primas; algunos procesos usados para su separación son por ultra y nano filtración, sin embargo, la mayoría de los métodos comerciales para cuantificar lactosa y proteínas no son exactos. En este trabajo se demuestra que la espectroscopía infrarroja es un buen método para cuantificar lactosa y proteína después de los procesos de ultra y nano filtración. Las curvas de calibración que se prepararon con esta técnica analítica midiendo soluciones acuosas de lactosa y proteína en el intervalo de 0 a 20%) de estos componentes, mostraron buena linealidad; después del 20%> la solución de lactosa se satura. La espectroscopia infrarroja mostró ser un método rápido y preciso que puede ser usada para cuantificar esos compuestos y dar seguimiento a los procesos de ultra y nano filtración aplicados para purificar lactosa y proteínas del suero.

Tungsten(VI) oxide can be easily synthesized starting from a standard light bulb. The reaction consists in the oxidation at high temperatures (T » 2000 - 3000° C) of a tungsten filament in presence of air; conditions which can be easily achieved by connecting a broken light bulb (but with its intact filament) to an AC-power supply of 110 volts. The vapor of WO3 is condensed into a beaker in a quantity enough to be characterized by infrared spectroscopy. The experiment is very funny, inexpensive and allows to the teacher to link several topics in current chemistry and physics of the tungsten oxides, such as their nomenclature and technological applications (i.e. electrochromic devices, gasochromic sensors, superalloys or as it is used in home: As a "simple" emisor of light!).