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18 October 2004 On the degradation of polymeric films confined at nanometer scale
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Degradation processes in confined polymeric films, with a thickness smaller or equal to 100 nm are of particular importance for future space missions and microelectronics applications. A simplified theoretical model for the evolution of free radicals in such films is proposed. The model takes into account the dependence of the glass transition temperature (TG) on the film thickness as well as the dependence of TG on the average molecular mass of the polymer (Fox-Flory equation), by exploiting the blob concept. It is assumed that the film thickness controls blobs' size. The time and temperature evolution of free radicals is desxcribed by dividing the main physical and chemical processes into two statistically independent steps. In the first step, the reactants diffuse towards a nanometer sized reaction volume. In the second step the proper chemical reaction between reactants occurs. Two possible chemical reactions are considered: the deactiviation of free radicals through chemical reactions with small molecules or free electrons and the recombination of free radicals. It is supposed that the diffusion of free radicals is a self-diffusion process that obeys a Williams-Landel-Ferry like temperature dependence. The temperature dependence of the diffusion coefficient of small molecules was assumed to obey a simple Arrhenius like dependence. This provides a simple theoretical approach for the modeling of the physical properties thin polymeric films subjected to degradation processes within the glass transition range and may be refined to assess the lifetime of such films in extreme environments.
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Mircea Chipara, David L. Edwards, and Mary Nehls "On the degradation of polymeric films confined at nanometer scale", Proc. SPIE 5554, Photonics for Space Environments IX, (18 October 2004);

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