Charge transfer processes in pulse-irradiated polymers
Polimery 1997, No 3, 162
Mobile electron—positive hole pairs were found to form in pulse-irradiated polyethylene (PE) and poly(methyl methacrylate) (PMMA) polymer matrices. Negative charges can be stabilized in PE as trapped electrons, ej, evident in near IR spectra (λ < 2000 nm) or, in PMMA, as radicalanions evident in the UV—VIS range (Fig. 1). Positive holes can be trapped in PE as the unsaturation centers in the polymer chain. In PMMA, positive (mobile) holes are transformed into radical centers by a fast proton transfer process. In the aromatic [pyrene (Pi); dimethyldiphenyl (DMD)j-doped polymer matrices, short-lived radical-ions are formed (Fig. 2) which recombine to produce excited singlet monomer and excimer states [Eqn. (6)]. After an irradiation pulse, both monomer and excimere mission is observed as delayed luminescence (Fig. 4). A second-order kinetic equation including a time-dependent constant can describe the kinetics of recombination (decay) of the solute radical-ions in the PE matrix. The Arrhenius-type equation describes the effect of temperature on the solute recombination rate constant. A two-segment linear plot was obtained and, with the PE matrix, the intersection point occurred at the glass transition temperature (Tg) (Fig. 3).