Dynamics of Concentrated Polymer Solutions Revisited:Isomonomeric Friction Adjustment and Its Consequences.

In concentrated polymer solutions,the concentration (ϕ) dependence of the terminal relaxationtime τdreflects ϕ-dependent changes of severalfactors, the monomeric friction ζ0(ϕ), theentanglement length, a(ϕ), and the correlationlength, ξ(ϕ). Usually, the effect of the latter two factorson τdcan be cast in a simple power law, τd∼ ϕv. This powerlaw form is to be examined for τdafter correctionof the changes of ζ0with ϕ, but this iso-ζ0correction is an unsettled problem. The correction basedon the concept of “iso-free-volume” has been attemptedin literatures. This study focused on four groups of solutions withdifferent local frictional environments to examine universal validityof this correction. The isothermal data of τdwererheologically measured, and then corrected to the iso-frictional (iso-ζ0) state. After this correction, τdof mostsolutions in small molecule solvents showed the power law behaviorτd∼ ϕvwithexponent of v= 2.0 ± 0.2, irrespective of thesolvent type, either neutral small molecules or an ionic liquid (organicsalt), and of the difference of the glass transition temperaturesof the solvent and polymer. In contrast, the exponent became smaller(v≈ 1.3) for the solutions in an oligomericsolvent. These results are discussed within the frame of the two-lengthscaling theory that considers changes of ξ and awith ϕ. [ABSTRACT FROM AUTHOR]