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

Dielectric segmental mode relaxation (the alpha-relaxation) was investigated for toluene solutions of poly(vinyl acetate) (PVAc) and for undiluted PVAc. The relaxation spectra in concentrated solutions were found to be much broad compared with those in the undiluted state and in dilute solution. It was also found that the relaxation spectra broadened with decreasing temperature near the glass transition temperature. For concentrated solutions, the correlation length of local heterogeneity (due to concentration fluctuation) was determined to be 1.0 nm by using small-angle X-ray scattering. On the basis of the assumption that the distribution of relaxation times in logarithmic scale is proportional to the magnitude of the heterogeneity, the temperature dependence of the broadness of loss curves can be explained. Thus, the broad dielectric relaxation spectra in concentrated solutions can be attributed to a local configurational irregularity of the polymer segments and the solvent molecules.