Precision viscometry of polyvinyl acetate in toluene

Abstract

Abstract The viscosity of dilute solutions of PVA in toluene is investigated as a function of shearing stress in an Ubbelohde precision viscometer which permits determining the efflux time to within 3 × 10 −3 sec. Various sources of error in capillary viscometry are discussed. Correction for drainage is made on the basis of a newly developed theory. In a first series of measurements uncorrected values of ( t − t 0 )/ t 0 c are shown to give an anomalous curve when plotted against c . In this series the effect of changes in concentration as a result of adsorption onto the walls of the dilution vessels is studied. The anomaly disappears when corrections are made for various sources of error and for non‐Newtonian behavior in particular (second series). The thickness of the adsorption layer on the wall of the capillary is estimated from results in two viscometers with different bore. A comparison with direct measurements of adsorption on glass beads reveals that the average density of the polymer adsorbed is about 0.17 g./ml. The viscosity at low shearing stress is an even function of the shearing stress. The intrinsic viscosity is markedly dependent on shear rate, its value at high shear rates being about 40% of that of zero shear rate.