Edson C. da Silva

Polyethylene and polypropylene surface modification by impregnation with manganese (IV) oxide

Abstract Polyethylene (PE) and polypropylene (PP) surfaces can be modified by impregnation with manganese dioxide, either pure or mixed with iron(III) and copper(II) oxides. This is done by immersion of polymer tubing or film in (acidic or alkaline) potassium permanganate aqueous solutions, at 50–80°C. The oxide deposits thus obtained are highly adherent to the polymer surface and resistant to mild (cloth, paper) abrasion. These polymer—oxide composites were studied by electron spin resonance (ESR) spectroscopy. ESR spectra of samples obtained under various conditions showed differences, depending on the preparation technique used and on the sample age. Spectral characteristics of the oxides indicate that the total amount and local concentration of Mn 2+ ions in the oxides can vary, depending on the preparation procedure.

Photoacoustic assessment of the in vivo genotypical response of corn to toxic aluminium.

An open-cell photoacoustic (OCPA) spectroscopic technique is described which can assess genetically rooted differences in the response of live specimens of corn (Zea Mays L.) to the toxic action of aluminium. Specimens from a susceptible and a tolerant inbred line were examined. The differences in their OCPA in vivo leaf spectra were evident and an interpretation is given based on the genetically controlled response of the inbreds to aluminium toxicity. An earlier discrimination among specimens is obtained with this technique than has been possible so far with previous techniques.

Characterization of human skin through photoacoustic spectroscopy

The photoacoustic technique is based on the absorption of modulated light by a sample and subsequent heat generation. This generates thermal waves that propagate in the surrounding media. According to the Rosencwaig-Gersho Model, such waves produce the pressure oscillation detected as the photoacoustic signal. This technique allows the spectroscopic characterization of multilayer systems: as the thermal diffusion length varies with the modulation frequency of the absorbed light, the depth profile of a sample can be studied by the analysis of the photoacoustic signal at different modulation frequencies. In this work, photoacoustic spectroscopy was used to characterize different human skin samples. Measurements were performed at 70Hz and 17Hz, using a 1000W Xe arc lamp as the light source, for wavelengths between 240nm and 700nm. Skin samples were about 0,5cm diameter. It was possible to obtain the photoacoustic absorption spectra of the stratum corneum and of a deeper layer of epidermis; when the lower modulation frequency is utilized, photoacoustic spectroscopy characterizes the absorption of the whole epidermis, because in this case the thermal diffusion length is thicker than that of the stratum corneum. Photoacoustic spectroscopy was also employed to monitor the drying kinetics of the skin. This was done by analyzing the time evolution of the photoacoustic spectra of skin samples. Pre-treatment of the samples included different periods in a drying chamber. Measurements show that the photoacoustic spectra changes according to the humidity of the skin. Future work includes detailed monitoring of skin hydration.

Sunscreen effects in skin analyzed by photoacoustic spectroscopy

In the photoacoustic technique, the signal is proportional to the heat produced in a sample as a consequence of modulated light absorption. This technique allows the spectroscopic characterization of multilayer systems: as the thermal diffusion length varies with the light modulation frequency, one can obtain the depth profile of the sample by analyzing the frequency-dependence of the signal. As the photoacoustic signal depends on thermal and optical properties of the sample, structural changes in the system under analysis account for signal variations in time. In this work, photoacoustic spectroscopy was used to characterize samples of sunscreen and the system formed by sunscreen plus skin. We used photoacoustic spectroscopy to monitor the absorption kinetics of sunscreen applied to samples of human skin, characterizing alterations in the human skin after application of sunscreen. Measurements used 250W Xe arc lamp as light source, for wavelengths between 240nm and 400nm. This range corresponds to most of the UV radiation that reaches Earth. Skin samples were about 0,5cm diameter. The absorption spectra of sunscreen was obtained. Finally, photoacoustics was employed to monitor the absorption kinetics of the sunscreen applied to skin samples. This was done by applying sunscreen in a skin sample and recording the photoacoustic spectra in regular time intervals, up to 90 minutes after application. According to measurements, light absorption by the system sunscreen plus skin stabilizes between 25 and 45 minutes after sunscreen application. Results show that this technique can be utilized to monitor drug delivery and farmacokinetics in skin samples.

Incorporation of oxygen in crystalline zeolitic chromosilicates: optical identification of chromium(VI) by photoacoustic spectroscopy

Incorporation of oxygen to crystalline zeolitic chromosilicates, with oxidation of anchored CrIII to non-interacting CrVI species, has been confirmed by photoacoustic spectroscopy; the dichromate anion being extracted from the chromosilicate with water and identified by precipitation of AgCrO4 and oxidation to CrO5.

Synthesis and spectroscopic characterization of CrIII in crystalline zeolitic silicates

The incorporation of CrIII into the framework of high content silica zeolite is confirmed by electron spin resonance and photoacoustic spectroscopies.