Self-Diffusion and Viscoelasticity in Concentrated Polymer Systems

I. Data Analysis

Abstract

Literature data on the self-diffusion coefficient D_s of linear polymers in bulk and solution have been reexamined. The major conclusions are as follows:
(a) The currently accepted relation for D_s as a function of polymer molecular weight M and concentration c_p, i. e., D_s∝M^-2,p^-1.75 (i) is not exactly followed by the data, though it is usually taken as evidence for the reptation motion of a polymer chain assumed in the tube theory and also for the scaling theory.
(b) The experimental data examined suggest that D_s tends to obey the relation D_s∝M^-2.5 (ii) for M>M_c, the critical molecular weight for the onset of entanglement, and D_s∝M_-1 (iii) for M<M_c, with a smooth transition between the two regions. Equation (ii) is consistent with the relation expected from viscoelastic data on polymer concentrates.