Synthesis and Characterization of the Monomer 2,2′ diallylbisphenol-A (ABFA) for obtaining Proton Exchange Membranes based on Crosslinked Sulphonated Poly(Arylene ether sulphone)s

Summary: In the present work, a methodology of synthesis and characterization of the monomer 2,2′ diallylbisphenol-A (ABFA) was developed, aiming at getting a precursor, with adequate purity, for obtaining cross-linked membranes based on sulphonated poly(arylene ether sulphone)s. The monomer synthesis involved the synthesis of 2,2′ bis(4-allyloxiphenyl)propane (Bisphenol-A, diallyl ether - BFAAE), from Bisphenol-A (BFA), followed by Claisen rearrangement of BFAAE, for the production of the target compound 2,2′ diallylbisphenol-A (ABFA). All the compounds, reagent BFA and obtained products, intermediate product BFAAE and final product ABFA, were characterized by FTIR (Fourier Transform infrared spectroscopy), TGA (Thermo-gravimetric analysis) and HPLC (High-performance liquid chromatography). The compound BFAAE was obtained with a yield of 94.5% and a purity of 97.3%, the latter characterized by TGA and by HPLC. The structure of the product was confirmed by FTIR. The thermal Claisen rearrangement process was conducted by using Differential Scanning Calorimetry (DSC) technique, from a factorial experiment planning, with two factors and three levels, with temperature and time being the variables. The above cited techniques were used for monitoring the Claisen rearrangement and for the characterization of the final product. The best results yield ABFA purity between 85 and 90%, approximately, for 220 °C/60min, 230 °C/30min and 210 °C/90min conditions. The obtained results suggest that, in the studied range, polymerization and degradation of the monomer ABFA occur, simultaneously to its formation.     

Meromorphic quadratic differentials with prescribed singularities

We study the singular flat structure associated to any meromorphic quadratic differential on a compact Riemann surface to prove an existence theorem as follows. There exists a meromorphic quadratic differential with given orders of the poles and zeros and orientability or non orientability of the horizontal foliation, iff these prescribed topological data are admissible according to the Gauss-Bonnet Theorem, the Residue Theorem and certain conditions arising from local orientability or non orientablity considerations. Some few exceptional cases remain excluded. Thus, we generalize two previous results. One due to Masur & Smillie, which assumes that poles are at most simple; and a second one due to Muciño-Raymundo, which assumes that the horizontal foliation is orientable.Partially supported by DGAPA-UNAM and CONACYT 28492-E.     

Electrochemical impedance study of GaAs surface charge modulation through the deprotonation of carboxylic acid monolayers

Modifications to the space charge region of p+ and p-GaAs due to surface charge modulation by the pH-induced deprotonation of bound carboxylic acid terminal monolayers were studied by electrochemical impedance spectroscopy and correlated to flat-band potential measurements from Mott-Schottky plots. We infer that the negative surface dipole formed on GaAs due to monolayer deprotonation causes an enhancement of the downward interfacial band bending. The space charge layer modifications were correlated to intermolecular electrostatic interactions and semiconductor depletion characteristics.     

XRD and SEM characterization of Cu/Co catalysts supported on Si-Al-zeolite made by a modified sol-gel technique

Cu, Co and Cu/Co catalysts supported on a Si-Al-Zeolite matrix, made by a modified sol-gel method, were characterized by XRD and SEM. The formation of some spinels was identified in some of the samples. Of particular interest were those spinels whose composition included Cu and Co in a mixed oxide. The identification of such structures would explain higher activities in those catalysts. This revised version was published online in June 2006 with corrections to the Cover Date.     

Density and Volumes of Mixing of the Ternary System Ethylbenzene + Styrene + Ethyl Acrylate and its Binaries at 298.15 K

Densities of the ternary system, ethylbenzene + styrene + ethyl acrylate, and its three binaries have been measured in the whole composition range at 298.15 K and atmospheric pressure using an Anton Paar DMA 5000 oscillating U-tube densimeter. The calculated excess molar volumes are positive for the binary system, ethylbenzene + ethyl acrylate, and negative for the systems ethylbenzene + styrene and styrene + ethyl acrylate. The corresponding data were correlated with the Redlich-Kister equation and with a series of Legendre polynomials. Several models were used to correlate the ternary behavior from the excess molar volume data of their constituent binaries and were found to fit the data equally well. The best fit was based on a direct approach, without information on the component binary systems.     

Three extra mirror or sequential families: case for a heavy Higgs boson and inert doublet

We study the possibility of the existence of extra fermion families and an extra Higgs doublet. We find that requiring the extra Higgs doublet to be inert leaves space for three extra families, allowing for mirror fermion families and a dark matter candidate at the same time. The emerging scenario is very predictive: It consists of a standard model Higgs boson, with a mass above 400 GeV, heavy new quarks between 340 and 500 GeV, light extra neutral leptons, and an inert scalar with a mass below M(Z).     

Langmuir Probe Measurements in a Grid-Assisted Magnetron Sputtering System

The grid-assisted magnetron sputtering is a variation of the magnetron sputtering commonly used for thin film deposition. In this work, Langmuir probe measurements were performed in such a system by using the grid under two basic and practical electrical conditions, i.e., floating and grounded. The results show that grounding the grid leads to an enhancement of the plasma confinement and to increases in both floating and plasma potential, as inferred from the probe characteristics. The grounded grid drains electrons from the plasma, acting as an auxiliary anode and reducing the plasma diffusion toward the chamber walls. For the same discharge current, the improved confinement results in a lower electron temperature when compared to floating condition, although the electron densities are comparable in both cases.     

Transpassivity characterization of the alloy UNS N08367 in a chloride-containing solution

We investigate the transpassivity of super-austenitic stainless steel UNS N08367 in 2.5 M LiCl solution by using cyclic potentiodynamic polarization (CPP), electrochemical impedance spectroscopy (EIS), and X-ray photoelectron spectroscopy (XPS). The CPP curve exhibits negative hysteresis, which indicates a transpassive dissolution process instead of pitting corrosion. The transition from the passive region to the transpassive region is characterized by EIS and equivalent circuit analysis. During the transpassive dissolution of the N08367 alloy, two reactions of adsorbed intermediates are dominant, as indicated by the two inductive loops at the transpassive region. The first inductive loop is associated with the faster reaction, i.e., the adsorption of Fe intermediates. This fast reaction is significantly influenced by the preferential dissolution of Fe during the transpassive dissolution. The second inductive loop is correlated with the adsorption of the Cr intermediate. In contrast to Fe, the Cr content on the surface increases in the transpassive region compared with the content in the passive region. The XPS spectra support the time and frequency domain approach for the preferential dissolution, and the dominant species resulted from the interfacial processes at the transpassive region.