Broadening of the fluorescence spectra of hydrocarbons in ethylene-vinyl acetate copolymers and the dynamics of the glass transition

摘要

The steady-state fluorescence of two fluorescent condensed aromatic hydrocarbons (anthracene adn pyrene) with different fluorescence decay rates(a few nansoseconds and hudreds of nanoseconds,respectively) were empolyed to invesigated the relaxation processes of several radnom ethylene-co-vinyl acetate copolymer (EVA).Copolymers with various comonomer compositons (EVA-9,EVA-18,EVA-25 and EVA_33)were studied.Data for the EVAs were compared with the same aromatic molecules in low-density polyethylene (LDPE),high-density polyethylene(HDPE) and poly(vinyl acetate) (PVAc) homopolymer models.The fluorescence rata constants were measured by single photon couniting at room temperature.The wavelength dependence of the emission spectra (the edge-excitation red-shift(EERS)) were studied at room temperature adn at 77 K nd the data were interpreted based on the correlation of the differences of decay rates for both molecules and the time correlation of the polymer relaxation processes.The spectral broadenings (full-width at half-mazimum (FWHM)) of the fluorescence spectra were studied from 20 to 400 k,which included temperature ranges above and below the glass transition,and there broadenings are compared.