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|Type:||Artigo de periódico|
|Title:||Temperature-dependent fluorescence from pyrenyl-modified polyethylene films. A comparison of attachment methods and morphology changes by irradiation with eV-range photons and bombardment with MeV-range positive ions|
|Abstract:||1-Pyrenyl groups were attached covalently to three polyethylene (Py-PE) films with different crystallinities by irradiating (eV-range photons-UV-photons) or by bombarding (MeV-range ions-protons and alpha particles) pyrene-doped PE films (Py/PE). Onset temperatures of relaxation processes (T-x) of the Py-PE were approximated from (1) Arrhenius-type plots of the normalized integrated intensities of the films and (2) the temperature dependence of the full-width half-maximum (FWHM) films and the position of the 0-0 fluorescence band. DSC thermograms of the native and irradiated or bombarded films were also compared to independently assess the morphological changes. The onset temperatures T-x in lower crystallinity Py-PE films were more difficult to locate when prepared by bombardment with high doses than with low doses of photons or ions or by irradiation. The ease of locating the T-x in higher crystallinity Py-PE films was independent of dose, suggesting little change in the mobility in the vicinity of pyrenyl probes. Fluorescence from Py-PE bombarded with alpha particles indicated the presence of both singly- and doubly-attached pyrenyl groups. The singly-attached pyrenyl groups were less sensitive than the doubly attached to the T-x. Py-PE films were more sensitive luminescence reporters of T-gamma segmental motions than were 9-anthryl groups covalently attached to the same polymers. We also discuss possible reasons why the values of the activation energies for the relaxation processes, as calculated from the Arrhenius plots, were much smaller than those based on the dynamic mechanical methods. (C) 2004 Wiley Periodicals, Inc.|
|Editor:||John Wiley & Sons Inc|
|Appears in Collections:||Unicamp - Artigos e Outros Documentos|
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