Dynamic melt rheology. I: Re‐examining dynamic viscosity in relationship to the steady shear flow viscosity

Abstract

AbstractSince 1950's, theoretical as well as experimental efforts have been made to explain the similarity between the shear rate dependence of the steady flow apparent viscosity and the frequency dependence of the dynamic viscosity. The literature points out agreements, as well as occasional disagreements, between the two viscosity terms, depending on the polymer system. In this manuscript, some critical results are presented which suggest that the strain rate dependence of the two viscosities, has entirely different origins and that it is only a coincidence that these data happen to be closer for the common polymers. A time‐temperature dependence of viscoelastic parameters is brought into the discussion to argue the observed pseudo‐plasticity in dynamic melt rheology and to demonstrate, in principle, that the strain rate dependence of the dynamic and steady flow viscosities should be different. Nevertheless, we must mention that the dynamic and steady flow measurements have their own merits and these techniques can complement each other very well.