Estudo da interaÃÃo entre compostos orgÃnicos volÃteis e filme finos de polipirrol

AUTOR(ES)
DATA DE PUBLICAÇÃO

2007

RESUMO

Conducting polymers can be used as active materials of sensing devices that find application in different areas, such as quality control of products in industries such as food and beverage, cosmetics and solvents, in the monitoring of air quality for environmental and safety purposes, and as an auxiliary tool in the diagnosis of diseases. In spite of this, as a general rule, the details of the prevailing interactions of the volatile compounds and the polymer are not well understood. For this reason, we have focused the work of this thesis on the characterization of the interactions between vapors of volatile organic compounds and thin films of polypyrrole. These films, that were the active components of the sensors, were prepared atop of common glass slides and conducting glass slabs via in situ polymerization, where several preparation parameters (such as the relative monomer/doping agents concentrations, the amount of oxidizing agent and the polymerization time) were controlled to assure an homogeneous growth of the polymeric film. UV-VIS-NIR spectra were used to obtain detailed information about the kinetics and the best amounts of time allotted for the polymerization of the different systems analyzed. We have also measured the contact angle of water, ethylene glycol and diiodomethane deposited on the surface of the polymeric films to evaluate how the use of different doping agents would influence their hydrophobicity and surface free energy (and its acid-base and dispersive components); a multivariate analysis of the data reveal not only a contrast between the hydrophobicity and the basic component of the surface tension, but also that the hydrophobic character increases with size of the aliphatic chain [number of aromatic rings] for the alkylsulphonic [aromatic] doping agents. The selectivity and sensitivity of the polymeric sensors when exposed to different volatile organic compounds (VOCs) have shown to be dependent not only of the properties of the analyzed VOC but also on the nature of the counter-ion used to dope the polypyrrole film. Polymeric blends prepared by vapor phase polymerization (with the films directly deposited on a conducting glass substrate) have exhibited a promising behavior as sensors of VOCs, especially because some of them present a sharp difference in their responses to polar and apolar compounds. As a final conclusion, we can say that as a result of this work it becomes possible to optimize the design of an arrangement of sensors such that both a better sensitivity and a better selectivity sensitivity to a given chemical environment can be achieved

ASSUNTO(S)

sensores quÃmicos contact angle chemical sensors surface energy Ãngulo de contato polypyrrole ciencias exatas e da terra energia superficial polipirrol

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