Static and Dynamic Fluorescence of Pyrene as Probes of Site Polarity and Morphology in Ethylene-co-(Vinyl Acetate) (Eva) Films

Abstract

Static and dynamic fluorescence of pyrene has been used to study the polarity of microenvironments of ethylene-co-(vinyl acetate) copolymers of varying compositions. The polarity of these copolymers, defined by the Py-scale, has been compared with low-density polyethylene and poly(vinyl acetate). Linear correlations between vinyl acetate content and either the vibronic ratio, I/III, of the pyrene fluorescence spectra or the fluorescence decay constants, τF, have been obtained. We have also studied the photophysical properties of pyrene sorbed on the polymer surface by vapor deposition or incorporated within the polymer by swelling with a solvent. The photophysical parameters determined by both experiments are virtually the same, demonstrating that pyrene senses the same type of environment throughout the polymer film. Furthermore, in each of the copolymers, the probes experience an average polarity rather than one from domains enriched in either ethylene or vinyl acetate.