Experimental studies of an entangled polystyrene solution in steady state mixed type flows

Abstract

Experimental measurements of birefringence and velocity gradient components are reported for steady mixed type flows of a 0.076 g/cm3 solution of 2.89×106 MW polystyrene in a mixed toluene/oligomer solvent. The flow field is produced in a co-rotating two-roll mill with a series of different ratios of the gap width to roller radius chosen so that the flow type at the stagnation point for a Newtonian fluid would range from 0.0196⩽λ⩽0.20, where ‖E‖/‖Ω‖=(1+λ)/(1−λ). Additional data are also reported, for comparison purposes, for a similar polystyrene solution in a simple Couette flow. Finally, the stress-optical relationship is used to obtain a generalized extensional viscosity as a function of strain rate. This viscosity shows a range of strain rate thinning as predicted by reptation theory, followed at a critical Weissenberg number of 0(1) based on the Rouse relaxation time by the initial stages of a region of strain rate thickening, as predicted by the Marrucci–Grizzuti extension of reptation theory that a...