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/τd and self-diffusion coefficient Ds of the long chains both decrease systematically with increasing short chain length NS and with the weight fraction φ of the long chain in the mixtures. The second set of data indicates that the short chain\u27s diffusion coefficient Ds decreases with increasing φ, leading to insightful comparison between the self-diffusion coefficient Ds at φ = 0 and trace diffusion coefficient Dtr in the limit of φ = 1.0: Dtr recovers the asymptotic molecular weight scaling of M-2.0, whereas Ds 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 Me are found to diffuse in entangled matrices of different chain length NL with a self-diffusion coefficient Ds that is independent of NL at all compositions