The viscosity of concentrated polymer solutions

Abstract

AbstractThe general equation for pseudoplasticity previously derived by an extension of Goodeve's impulse theory of viscosity is derived specifically for polymer solutions by a consideration of the rate of energy dissipation in a sheared solution. Its general application to polymer solutions is discussed with particular reference to the fact that unlike other theories it is capable of explaining the linear relation between fluidity and shear stress at very low shear stress, frequently observed, as well as the dependence on the square of the shear stress predicted by other theories. The application to data obtained with aqueous methyl cellulose solutions at moderate shear rates is outlined. The onset of structural viscosity at a more or less critical concentration is explained by a definite type of mechanical interlocking which does not occur in dilute solutions. The average binding energy of an effective molecular entanglement was estimated at about 7kT units and was independent of concentration. The rate constants for shear induced link formation and rupture appeared to be independent of concentration. The corresponding rate constants in the absence of shear appeared to decrease with increased concentration, presumably due to a decreased rate of diffusion as suggested by the theories of Smoluchowski and Kramers.