Describing the relaxation spectrum of entangled homopolymer blends with the dynamic random-phase approximation

Detailed calculations of the intermediate scattering function of entangled, binary homopolymer blends are presented. The calculations are based on the reptation model of polymer dynamics and employ the dynamic random-phase ap proximation for inferring collective blend behavior from single-chain chara cteristics. The relaxation spectra found here for blends-including the rela xation rates and amplitudes of higher-order modes-a-re contrasted with thos e for melts and are given for the entire range of length scales from the di ffusive to the nondiffusive regime of polymer dynamics. Analytical limits o f the intermediate scattering function are successfully compared to numeric al results. The dominance of higher-order relaxation modes in specific, exp erimentally feasible, asymmetric blend systems is indicated, and the possib ility of significant deviations of the expected time-correlation functions from a single-exponential decay is noted.