Effect of local heterogeneity on dielectric segmental relaxation of poly(vinyl acetate) in concentrated solution

Dielectric segmental mode relaxation (the alpha-relaxation) was investigate d for toluene solutions of poly(vinyl acetate) (PVAc) and for undiluted PVA c. The relaxation spectra in concentrated solutions were found to be much b road compared with those in the undiluted state and in dilute solution. It was also found that the relaxation spectra broadened with decreasing temper ature near the glass transition temperature. For concentrated solutions, th e correlation length of local heterogeneity (due to concentration fluctuati on) was determined to be 1.0 nm by using small-angle X-ray scattering. On t he basis of the assumption that the distribution of relaxation times in log arithmic scale is proportional to the magnitude of the heterogeneity, the t emperature dependence of the broadness of loss curves can be explained. Thu s, the broad dielectric relaxation spectra in concentrated solutions can be attributed to a local configurational irregularity of the polymer segments and the solvent molecules.