Steady and transient shear flows of polystyrene solutions I: Concentration and molecular weight dependence of non-dimensional viscometric functions

Abstract

Start up from rest and relaxation from steady shear flow experiments have been performed on monodisperse polystyrene solutions with molecular weight ranging from 1.3 × 10 5 to 1.6 × 10 6 and concentration c ranging from 5% to 40%. A method of reduced variables based on the use of a characteristic time τ w is proposed. τ w is defined as the product of zero shear viscosity with the steady state elastic compliance. Reduced steady and transient viscometric functions so obtained depend on the ratio M/ M e (where M e is the entanglement molecular weight). Limiting forms are obtained when M/ M e ⩾ 18. In steady flow, a simple correlation is found between shear and normal stresses. In stress relaxation experiments, independent of shear rate, the long-time behaviour can be characterised by a single relaxation time τ 1, which is identical for shear and normal stresses. τ 1 can be simply related to the zero shear rate viscosity and the limiting elastic compliance.