A study of hydrodynamic interactions of macromolecules in solutions by means of precision viscometry

Abstract

A precision capillary viscometer with a photoelectric timer has been designed and built for these investigations. On the assumption that the relative viscosity can be expanded in a power series in concentration, the intrinsic viscosity and the coefficient of the second order term have been measured for suspensions of sperical and rigid rodlike macromolecules. The viscosity of a known heterogenous suspension of rods and spheres has been determined and has been interpreted in terms of interaction coefficients. The Einstein theory of viscosity of dilute suspensions of spheres has been modified to form, together with the approaches of Burgers and Jeffery, a logically consistent theory for the intrinsic viscosity of spherical molecules in particular, and ellipsoid particles in general. The second order theory in volume fraction for the viscosity of suspensions was reviewed. Previous work in this field was found to be in error. It was shown that, when properly interpreted, the linear solution of Burgers to the problem of the viscosity of dilute suspensions of spheres fully explains the variation of the relative viscosity with concentration. The linear theory of Burgers did not adequately explain the variation of the relative viscosity of rod-like molecules with concecntration. This was attributed to mutual orientation effects. The study of the system consisting of rods and spheres also indicated that orientation effects might be important.