A New Variable Shear Capillary Viscometer

Abstract

<p> Since Newton's definition of viscosity does not lead to a useful description of non-Newtonian flow, two other model liquids, the Maxwell liquid and the Prandtl-Eyring liquid are discussed. Equations describing the flow behaviour of these liquids in narrow capillaries are derived and discussed. </p> <p> A thorough analysis is given of corrections that are, or may be, necessary in capillary viscometry, and the influence of non-Newtonian flow on these corrections is discusses, both for cylindrical and spherical bulbs. </p> <p> The significance of measurements of non-Newtonian flow in dilute solutions of macromolecules is discussed in terms of recent theories. It is shown that a capillary viscometer has inherent limitations for such measurements, but that a properly designed capillary viscometer can give precise and reliable data at shear rates down to 50 sec^-1, provided that the system is not too shear-dependent. </p> <p> A new variable shear capillary viscometer-- a modification of the Ubbelohde suspended level viscometer-- is describes. It was designed to be rugged, convenient and precise, to eliminate or minimize the kinetic energy correction and surface tenison effects, and to permit dilution of a solution while in the instrument. Three different viscometers of this type have been constructed, calibrated and tested, and proved sound in design and convenient in use. </p> <p> The usefulness of the viscometers has been demonstrated in three diverse investigations: (i) the shear dependence in aqueous solutions of a high molecular weight dextran, (ii) the temperature dependence of the zero-shear intrinsic viscosity in a good solvent of a very high molecular weight fraction of polystrene, (iii) the shear dependence of the interaction coefficient k' in the systems polystyrene-toluene and poly(n-octyl-methacrylate). </p>