Bidimensional Spectroelectrochemistry Applied to the Electrosynthesis and Characterization of Conducting Polymers: Study of Poly[4,4′‐bis(butylthio)‐2,2′‐bithiophene]

The electropolymerization mechanism of 4,4′‐bis(butylthio)‐2,2′‐bithiophene ( 1 ) was studied by means of bidimensional spectroelectrochemistry. Simultaneous electrochemical and spectroscopic signals were analyzed with the aim of obtaining information about the role of the low‐molecular‐weight oligomers in the polymerization process. Experiments in electrochemical cells with finite (thin layer) and semi‐infinite diffusion geometries were carried out to elucidate the role the oligomeric species play, both in the nucleation step and in the subsequent growth of the polymer deposited onto the electrode surface.     

Leaf protein from ammonia-treated dwarf elephant grass (Pennisetum purpureum) schum cv. mott)

Proteins can be an excellent by product of the biorefining of lignocellulosic materials. In this work, extraction conditions for the white leaf proteins (cytoplasmic) of ammonia-treated dwarf elephant grass were established to obtain a protein juice suitable for the production of leaf protein concentrates. A calcium hydroxide solution was used as extracting agent, at several solid-liquid ratios, pHs, temperatures, and times. Extractions were carried out in Erlenmeyer flasks containing 5 g (dry basis) of forage with constant agitation (100 rpm). The soluble protein content was determined by the Lowry method. Optimal extraction conditions for the ammonia-treated forage were 12.60 pH, 1:10 solid-liquid ratio, 90°C, and 30 min extraction time, resulting in 52.65% extraction yield. The ammonia treatment significantly increased (p<0.05) the release of proteins from the fibrous matrix, facilitating their extraction.     

Experimental model of cracking induced by drying shrinkage

Drying induced shrinkage in materials may yield the formation of surface crack patterns. We report on various experimental observations of the geometry of the crack array and the kinetics of crack formation on a model system consisting of a layer of a paste made of clay, sand, and water deposited on a rigid substrate. We investigate in detail the influence of the layer geometry (size and thickness). Received 19 April 1999     

Methane adsorption in PIM-1

We report the results of Grand Canonical Monte Carlo (GCMC) simulations of methane adsorption in a prototypical polymer of intrinsic microporosity, PIM-1. Polymer chains were represented with a united-atom model, with Lennard-Jones parameters obtained from the TraPPE potential. Additionally, partial charges were calculated from ab initio methods using Gaussian (HF/6-31G^* basis set). Samples of PIM-1 were built at low density conditions, followed by a Molecular Dynamics compression protocol until densities of 1.2 g?cm^?3 were achieved. This protocol proved to be suitable for the realistic modeling of the amorphous structure of PIM-1. Surface areas and pore size distributions were measured and compared to available experimental data. The simulated pore size distribution present a peak at 4.3 Å, consistent with experimental results. GCMC simulations of methane adsorption were performed, and found to qualitatively reproduce the shape of the available experimental isotherm.     

Selective ablation with UV lasers of a-Si:H thin film solar cells in direct scribing configuration

Monolithical series connection of silicon thin-film solar cells modules performed by laser scribing plays a very important role in the entire production of these devices. In the current laser process interconnection the two last steps are developed for a configuration of modules where the glass is essential as transparent substrate. In addition, the change of wavelength in the employed laser sources is sometimes enforced due to the nature of the different materials of the multilayer structure which make up the device. The aim of this work is to characterize the laser patterning involved in the monolithic interconnection process in a different configurations of processing than the usually performed with visible laser sources. To carry out this study, we use nanosecond and picosecond laser sources working at 355 nm of wavelength in order to achieve the selective ablation of the material from the film side. To assess this selective removal of material has been used EDX (energy dispersive using X-ray) analysis, electrical measurements and confocal profiles. In order to evaluate the damage in the silicon layer, Raman spectroscopy has been used for the last laser process step. Raman spectra gives information about the heat affected zone in the amorphous silicon structure through the crystalline fraction calculation. The use of ultrafast sources, such as picoseconds lasers, coupled with UV wavelength gives the possibility to consider materials and substrates different than currently used, making the process more efficient and easy to implement in production lines. This approach with UV laser sources working from the film side offers no restriction in the choice of materials which make up the devices and the possibility to opt for opaque substrates.     

Spin conversion detected by Mössbauer spectroscopy and μSR on a 1D FeII paramagnetic chain

While magnetic properties of the 1D chain [Fe(hyetrz)₃](4-bromophenylsulfonate)₂ investigated over the temperature range from 300 K to 2 K show paramagnetic behavior, detailed ⁵⁷Fe Mössbauer and muon spin relaxation measurements reveal an unexpected spin conversion. Approximately ~14 % of the high-spin ions are found to convert to the low-spin state with a transition temperature T _1/2?~?120 K.     

Convergence of the increments of a stochastic integral associated to the stochastic wave equation

We study a type of one-dimensional wave equation on the plane with non-linear random forcing. We are interested in the almost sure behaviour of the normalized increments of the solution process associated to this type of wave equation. Also we study the behaviour of the normalized increments of some other stochastic integral equation.