Polymethyl methacrylate mixtures with some organic laser dyes - I. Dielectric response

Solid samples of polymethyl methacrylate (PMMA) free and mixed with coumarin-6 or fluorescein sodium organic laser dyes have been prepared by a casting method. The dielectric parameters such as dielectric permittivity (epsilon') and dielectric loss (epsilon ") have been measured as a function of temperature and frequency. Both dyes have an increasing effect on both the magnitude and rate of increase of (epsilon') with temperature. The absorption peaks obtained in the epsilon "(T) spectra were analysed and interpreted. For the pure polymer, two regions were distinguished in both the relaxation spectra and Arrhenius plot of relaxation times. These were assigned to a beta process at lower temperatures and an alpha beta one at higher temperatures with activation energy values of 16.1 and 21.6 kcal/mol respectively. Coumarin-6 dye-doped sample exhibited an entirely plastification effect reflected in lower values of the temperature of epsilon(max)" the activation energy and beta factor of the non-Debye behaviour for the distribution of relaxation times. On the other hand, in fluor escein sodium dye-doped sample, the presence of the dye hinders the alpha process of the host polymer due to intermolecular interactions between the polymer molecules and the solute dye. (C) 1999 Elsevier Science Ltd. All rights reserved.