Rheology of Polymer Systems

Abstract

The steady state and dynamic viscosity are the most important rheological properties of polymer systems which can be correlated with molecular structure of the polymer involved. In dilute solutions the extrapolation to infinite dilution yields the intrinsic viscosity which at zero gradient is proportional to the average volume of the randomly coiled macro-molecule. Its dependence on gradient and frequency is closely connected with the change of hydrodynamic interaction with coil deformation and the coil deformability in flow depending on internal coil viscosity and finite chain length of the polymer. In concentrated solutions and melts the chain entanglements are enormously increasing the molecular weight, gradient and frequency dependence of viscosity. Particularly the gradient and frequency dependence with a drastic almost discontinuous drop from ηo to η∞ at high entanglement density turns out to be completely different from that of isolated molecules. No theoretical explanation is yet available for the close similarity of the gradient and frequency dependence of viscosity of isolated and concentrated polymer systems.