Plasma polymerized acetaldehyde thin films for retention of volatile organic compounds

The aim of this work is the production and characterization of plasma polymerized acetaldehyde thin films. These films show highly polar species, are hydrophilic, organophilic and easily adsorb organic reactants with CO radicals but only allow permeation of reactants with OH radicals. The good step coverage of films deposited on aluminum trenches is useful for sensor development. Films deposited on hydrophobic substrates may result in a discontinued layer, which allows the use of preconcentration in sample pretreatment. Deposition on microchannels showed the possibility of chromatographic columns and/or retention system production to selectively detect or remove organic compounds from gas flows.

Use of thin films obtained by plasma polymerization for grain protection and germination enhancement

In this work, preliminary results of the use of hydrophobic thin films obtained by plasma deposition to protect grains and seeds are presented: grains coated by the films did not present biological degradation when stored in a saturated water vapor environment, but had their germination accelerated in the presence of water. A model that explains the difference of behavior of the films when exposed to water in vapor form or in liquid form, based on the formation of microchannels within the film that lead to water uptake in seeds, is presented. The model was successfully tested using quartz crystal measurements, which showed that the microchannels within the films can favor the adsorption and permeation of water when the films are immersed in water.

Fotocromismo em filmes finos de óxidos de tungstênio de diferentes composições

Tungsten oxide thin films with three different compositions were deposited by reactive sputtering in an oxygen-argon plasma. In a system composed of a home made photochemical reactor coupled with an optic fiber spectrophotometer, the photochromic effect was studied in these oxide films as function of UV irradiation time, in ethanol, methanol and formaldehyde atmospheres. It was observed that the photochromic efficiency depends on the vapor chemical nature where the film is irradiated as well as the film composition. Kinetic analysis suggest that two kinds of optical absorption centers should respond by the photochromic effect in these films, one generated at film surface and other inside it, which one presenting a different time constant.

Preparation and electrochemical characterization of Pt nanoparticles dispersed on niobium oxide

Electrodes consisting of Pt nanoparticles dispersed on thin films of niobium oxide were prepared onto titanium substrates by a sol-gel method. The physical characterization of these electrodes was carried out by X-ray diffraction, scanning electron microscopy and energy dispersive X-ray analysis. The mean size of the Pt particles was found to be 10.7 nm. The general aspects of the electrochemical behavior were studied by cyclic voltammetry in 1 mol L-1 HClO4 aqueous solution. The response of these electrodes in relation to the oxidation of formaldehyde and methanol in acidic media was also studied.