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|Type:||Artigo de periódico|
|Title:||Dye-polymer interactions controlling the kinetics of fluorescein photobleaching reactions in poly(vinyl alcohol)|
|Abstract:||This work presents results for the temperature dependence of the photobleaching reactions of Fluorescein dissolved in poly(vinyl alcohol) (PVA) irradiated by a continuous 150 W Hg high pressure are lamp. We observed that the photobleaching process efficiency is dependent on: lamp power, dye concentration and temperature. Although the photobleaching processes can only be described by a single-exponential function for lower concentration samples, a biphasic model must be employed for intermediate concentrations, resulting in one slower and one faster processes, while, for higher concentration samples, even multiple-exponential functions are unable to fit the experimental data. This complex behavior is probably due to the co-existence of many different types of energy transfer and photochemical processes with different rate constants. Therefore, a model based on a sequential distribution of site occupation by the dye molecules in the matrix, controlled by dye-polymer interaction strengths, is proposed to explain the complex-exponential kinetic behavior. Moreover, photobleaching process efficiency is somewhat increased by temperature and, above the PVA glass transition temperature, T-g, (350 K), it follows a first order kinetics, fitted by a mono-exponential function. (C) 1998 Elsevier Science S.A. All rights reserved.|
|Editor:||Elsevier Science Sa|
|Appears in Collections:||Unicamp - Artigos e Outros Documentos|
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