Influence of Rate of Shear on the Apparent Viscosity of A—Dilute Polymer Solutions, and B—Bulk Polymers

Abstract

The measuredviscosity of bulk polymers and their solutions varies with the magnitude of the applied shearing stress. In this paper we show that this is a natural consequence of the fact that the molecules are caused to rotate by the shearing action. This rotation gives rise to sinusoidal forces which alternately stretch and compress the molecules. The viscous behavior of such a system is shown to be analogous to that of a spring immersed in a viscous medium and being acted upon by sinusoidal viscous forces. We have treated the problem quantitatively using the method of a previous paper. Good agreement is obtained between theory and experiment without the aid of adjustable parameters. It is found that, if the molecule is considered shielded, the theory accurately represents the experimental data for dilute solutions. The behavior of the bulk polymer is well represented by means of the free draining approach. It is pointed out that the variation of the viscosity of dilute polymer solutions with the rate of shear may provide a convenient method for determining molecular weights of coiling type polymers.