Diffusion and rheology of binary polymer mixtures

This work studies the diffusion and rheological behavior of binary mixtures (of long and short chains) based on 1,4-polybutadiene over the full composition range as a function of both long and short chain lengths using pulse-gradient NMR spin echo and oscillatory shear measurements. The first set of rheological and diffusion measurements reveals that the terminal relaxation rate 1/tau(d) and self-diffusion coefficient D-s of the long chains both decrease systematically with increasing short chain length N-S and with the weight fraction phi of the long chain in the mixtures. The second set of data indicates that the short chain's diffusion coefficient D-s decreases with increasing phi, leading to insightful comparison between the self-diffusion coefficient D-s at phi = 0 and trace diffusion coefficient D-tr in the limit of phi = 1.0:D-tr recovers the asymptotic molecular weight scaling of M-2.0, whereas D-s scales nonideally as M-2.4 due to the considerable constraint release effect in the explored range of molecular weight. Third, short chains of molecular weight below M-e are found to diffuse in entangled matrices of different chain length N-L with a self-diffusion coefficient D-s that is independent of N-L at all compositions.