D. Windmöller

Polyetherimide–silicone: a 10 µm ultrathin composite membrane for faster and more sensitive membrane introduction mass spectrometry analysis

A polyetherimide (polyester)/silicone (PEI/S) sheet composite membrane with a 10 µm thick cross-linked silicone layer is found to display the required mechanical properties to work efficiently as the solution/high vacuum interface in membrane introduction mass spectrometry (MIMS) analysis of volatile organic compounds (VOC) in water. Owing to much shorter response and recovery times, the PEI/S membrane allows much faster analysis and calibration procedures as compared to the 250 µm silicone membrane usually used in MIMS. When using EI, owing to excessive water permeation, responses (signal intensity) for the PEI/S membrane are not always superior, being analyte-dependent. For the more polar VOCs, however, the PEI/S membrane shows 2–3 times greater responses, improving their relatively poor MIMS detection limits. When water–methane chemical ionization is applied, the problem of excessive water permeation is attenuated, and the PEI/S membrane displays greatly superior responses.

Solid Eu(III) complexes studied by positron annihilation, optical and Mössbauer spectroscopies: insights on the positronium formation mechanism.

In this work, positron annihilation lifetime (PALS), Doppler broadening annihilation radiation lineshape (DBARL), Mössbauer and optical spectroscopies measurements were performed in Eu(III) dipivaloylmetanate complex, Eu(dpm)(3), at 295 and 80 K. The Eu(dpm)(3) complex is not luminescent at 298 K and does not form positronium. On the other hand, it is highly luminescent at 80K, but still does not form positronium. The absence of positronium formation at 80K cannot be explained by a ligand/metal charge transfer process. We found strong evidences that the electronic delocalization does not occur at both temperatures. Despite the Mössbauer results being inconclusive regarding the Eu(III)/Eu(II) reduction hypothesis, previous results showing positronium formation in other Eu(III) complexes suggest that this process is not occurring. Thus, more studies are needed to explain the absence of positronium in Eu(III) complexes.

NANOCOMPÓSITOS DE POLIURETANA TERMOPLÁSTICA E NANOTUBOS DE CARBONO DE PAREDES MÚLTIPLAS PARA DISSIPAÇÃO ELETROSTÁTICA

Polyurethane/multi-walled carbon nanotube (MWCNT) nanocomposites have been prepared with nanotube concentrations between 0.01 wt% and 1 wt%. MWCNT as-synthesized samples with ~74 nm diameter and ~7 μm length were introduced by solution processing in the polyurethane matrix. Scanning electron microscopy (SEM) images demonstrated good dispersion and adhesion of the CNTs to the polymeric matrix. The C=O stretching band showed evidence of perturbation of the hydrogen interaction between urethanic moieties in the nanocomposites as compared to pure TPU. Differential scanning calorimetry and positron anihilation lifetime spectroscopy measurements allowed the detection of glass transition displacement with carbon nanotube addition. Furthermore, the electrical conductivity of the nanocomposites was significantly increased with the addition of CNT.

MIMS evaluation of pervaporation processes

The potential of MIMS (membrane introduction mass spectrometry) to study pervaporation processes through a polydimethylsiloxane (PDMS) membrane is demonstrated. From the MIMS profiles of aqueous alcohol solutions (ethanol, propan-1-ol, propan-2-ol, butan-1-ol, 2-methylpropan-2-ol, pentan-1-ol, 2-methylbutan-2-ol, cyclohexanol), diffusion coefficients and fluxes were calculated. The diffusion of chloroform, phenol, toluene and chlorobenzene was also studied. Selectivity (α) and enrichment (β) pervaporation factors have been obtained for ethanol–water solutions.

Evidence of the Participation of Electronic Excited States in the Mechanism of Positronium Formation in Substitutional Tb1-xEux(dpm)3 Solid Solutions Studied by Optical and Positron Annihilation Spectroscopies

Positron annihilation lifetime (PALS) and photoluminescence spectroscopies measurements were performed in Tb(III) and Eu(III) dipivaloylmethanates, Tb(dpm)3 and Eu(dpm)3, and also on their binary solid solutions of general formula Tb1-xEux(dpm)3. A correlation between the 5D4 Tb(III) energy level lifetime and the positronium formation probability was observed, indicating that the ligand-to-metal charge transfer LMCT states act in both luminescence quenching and positronium formation inhibition. From these results, a new model is proposed, showing that excited electronic states have a relevant role in the positronium formation mechanism.