Alicia Larena
Technical University of Madrid
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Featured researches published by Alicia Larena.
Applied Surface Science | 1995
Alicia Larena; Gabriel Pinto; Felipe Millán
Abstract An experimental study on geometrical thickness measurements of photoconductor polymer coatings on thermoplastic polyester film substrate used as commercially available recording holograms is reported. The bases of these measurements which enable the evaluation of both total and coating thicknesses are the interference visible and infrared absorption spectra and the absorbance value of a band caused by the photoconductor coating in the infrared spectrum. A new technique, based on the Lambert-Beer law is proposed in order to obtain the thickness measurement of the coating.
Spectroscopy Letters | 1992
Alicia Larena; M. C. Matías; J.Martínez Urreaga
Abstract Fourier Transform Infrared Spectroscopy and Thermal Analysis have been used to study the thermal and termooxidative degradation of polysiloxane coatings obtained by treating E-glass fiber with aqueous solutions of 3-chloropropyltriethoxysilane. Initial weight losses were due to polymerization of the coatings. Severe oxidative degradations were observed at temperatures above 180°C. At 550°C the residue of the coating was found to be silica with free silanol groups.
Monatshefte Fur Chemie | 1991
Alicia Larena; Joaquín Martínez-Urreaga
SummaryThe chemiluminescent reaction of lucigenin with basic hydrogen peroxide has been studied in several mixtures of water with the cosolvents methanol, ethanol, 1-propanol, dimethylformamide, and dimethylsulfoxide. The chemiluminescence spectra depend on the cosolvent and its concentration in the reaction medium. With increasing cosolvent concentration, the chemiluminescence shifts to lower wavelengths. For similar cosolvents, the size of this shift increases with decreasing dielectric constant. In high-cosolvent-concentration mixtures, the chemiluminescence matches the fluorescent emission of N-methylacridone. Chemiluminescence from low-cosolvent-concentration mixtures is explained as the sum of the lucigenin and N-methylacridone fluorescent emissions, the lucigenin emission probably being a consequence of energy transfer from N-methyl-acridone. The cosolvent inhibits this energy transfer. These observations, taken together with our previous kinetic results, indicate that the reaction mechanism is the same in all the studied reaction media.ZusammenfassungDie Chemilumineszenzreaktion von Lucigenin mit basischem Hydrogenperoxid wurde in verschiedenen Mischungen von Wasser mit Methanol, Ethanol, 1-Propanol, Dimethylformamid oder Dimethylsulfoxyd untersucht. Die Chemilumineszenzspektren hängen vom organischen Kosolvens und dessen Konzentration im Reaktionsmedium ab. Mit ansteigender Konzentration ergeben sich in der Chemilumineszenz Verschiebungen zu größeren Wellenlängen. Für ähnliche Kosolventien steigt diese Verschiebung mit kleineren Dielektrizitätskonstanten an. Bei hohen Kosolvenskonzentrationen gleicht die Chemilumineszenz der Fluoreszenzemission von N-Methylacridon. Die Chemilumineszenz bei kleinen Kosolvenskonzentrationen kann als die Summe der Fluoreszenzemission von Lucigenin und N-Methylacridon erklärt werden, wobei die Lucigeninemission vermutlich eine Folge eines Energietransfers von N-Methylacridon ist. Das Kosolvens verhindert diesen Energietransfer. Diese Beobachtungen, zusammen mit früheren kinetischen Resultaten, erlauben den Schluß, daß der Reaktionsmechanismus in allen Reaktionsmedien der gleiche ist.
Optical Materials | 2001
Alicia Larena; Marcelo A. Villar
Abstract Optical properties, such as transmittance and diffuse reflectance in the range of 200–800 nm, of hot-pressed films of poly(ethylene-co-vinyl acetate) filled with up to 10 wt% of calcium carbonate were analyzed. A linear relationship between optical properties and film thickness was found for these composites. In the range of compositions analyzed, transmittance of films decreases with an increasing in the filler content following an exponential law. The amount of decreasing can also be related to the average statistics particle diameter for a constant weight fraction of added filler by a square root law. Diffuse reflectance of the films was very low in the visible zone and increases considerably in the UV zone.
Materials Letters | 1991
Alicia Larena; Gabriel Pinto
Abstract With the help of mechanical stylus instruments the geometry of polymer film surfaces can be determined directly. The relation between the statistically calculated average roughness, Ra, and the reflectometrical value with incidence angle of light of 60°, R′60, for polyethylene films, can be described by the equation R′ 60 = a + b R a , (where a and b are constants). By using this relationship, the magnitude of reflectometrical value of such materials can be used directly as a quantitative measure of film surface roughness.
Spectroscopy Letters | 1992
Alicia Larena; Gabriel Pinto
Abstract A study about the interference fringes caused in the infrared region by polymer films and their applications to the evaluation of some properties is reported. Interference fringes, a sinusoidal waveform superimposed on the baseline, arise from reinforcement and destructive interference of various wavelengths of radiation reflected from the internal surfaces of the film when the IR spectrum is carried out. An optical interference method is proposed for measuring the thickness and the refractive index, both within an accuracy better than 1%, and for evaluating the surface texture of polymer films. Each one of these procedures is explained by its application for polypropylene, polystyrene and polyethylene films, respectively, three commercially available industrial films widely used for packing and membranes. These methods can easily be extended to any fair thin film of transparent or weakly absorbing solid materials.
Materials Letters | 1990
Alicia Larena; Gabriel Pinto
Abstract Several polyethylene film surfaces were examined by the reflectometry technique by using different incidence angles of light. A logarithmic relationship has been found between the measured reflectometrical values using different incident angles.
Polymer Degradation and Stability | 1992
Alicia Larena; M.U. de la Orden; J. Martínez Urreaga
Abstract The effect of E-glass short fibre on the degradation of polypropylene was studied by thermogravimetric and differential thermal analysis. This filler catalyses degradation at low temperature, particularly in air, catalysis being strongly dependent upon the nature of the fibre surface; catalysis is prevented by pretreatment with HCl, which partly dissolves the soluble oxides of the fibre surface and intensely hydrates the fibre.
Journal of Colloid and Interface Science | 1992
Alicia Larena; M.U. de la Orden; J. Martínez Urreaga
Abstract Thermal analysis and Fourier transform-infrared (FT-IR) spectroscopy were used to study the nature of the coatings deposited on E-glass short fibers by treatments with methylvinyldichlorosilane (MVDCS) and vinyltrichlorosilane (VTCS) applied from various reaction media. The coatings obtained from aqueous or toluene solutions of both silanes were polysiloxanes and showed high thermal stability in a nitrogen atmosphere. However, in an air atmosphere, vinyl group oxidation occurred at temperatures near 200°C. Coatings obtained from toluene solutions in the presence of pyridine consisted mostly of pyridinium chloride, which could be removed by heating at 100°C. After heating at 100°C, a coating consisting of polyvinylsiloxanes subsisted on fibers treated with VTCS. However, no stable coatings were obtained from MVDCS under these reaction conditions.
Spectroscopy Letters | 1989
Alicia Larena; J. Sanz; J. V. Alonso; Gabriel Pinto
Abstract In the aim to improve the filtration process in the beer ma nufacture, a study on the beer turbidity have been made using two different techniques: nephelometry and V-UV spectrometry. Even though the former is the most commonly used, we propose the use of V-UV spectrometry since it is possible to follow the performace - of all the filtration line, not only in a punctual way but in a - wide range of wavelenghts. From the results of this work we deduce that V-UV spectrometry offers a better quality of results than nephelometry, being more useful in rutin periodic controls.