2022 年 50 巻 5 号 p. 371-385
For a type-A Rouse chain, a recent study derived an analytical expression of its dielectric loss εʺ under steady shear in terms of the basic Rouse parameters, the spring strength κ, the friction coefficient ζ, and the mean-square Brownian force intensity B, all being allowed to arbitrarily change with the Weissenberg number Wi (= shear rate multiplied by the longest relaxation time at equilibrium) and the latter two having a tensorial form; see Sato et al., Nihon Reoroji Gakkaishi, 50, 253 (2022). As a follow up, we have conducted a rheo-dielectric test for a type-A unentangled melt, poly(butylene oxide) with the molecular weight of 16 × 103, to measure εyʺ in the velocity gradient (y) direction as well as the viscosity η and the first normal stress difference coefficient Ψ1. Both dielectric relaxation time and intensity were found to decrease on an increase of Wi up to the onset of rheological nonlinearity (Wi ~ 1) where η and Ψ1 exhibited moderate thinning, but the dielectric relaxation mode distribution was not affected by this increase of Wi. Analyzing those εyʺ, η, and Ψ1 data on the basis of the above expressions, we found that κ increases moderately (by ~ 40 %) but the off-diagonal components of ζ remains negligibly small on that increase of Wi. We also found that the diagonal components ζxx (with x being the velocity direction) and Byy hardly change but ζyy decreases moderately (by ~ 20 %). These results, suggesting the onset of the finite extensive nonlinear elasticity as well as a violation of a relationship Byy ∝ ζyy (naively expected from the fluctuation-dissipation theorem), serves as a good starting point for deeper investigation of κ, ζ, and B.
