The low-shear limit of the effective viscosity of a solution of charged macromolecules

Abstract

The effect of pair interactions between charged macromolecules on the bulk stress is calculated for the Newtonian low-shear limit. Electrostatic force laws are derived for molecular conformations corresponding to the limits of weak and strong intramolecular repulsions and used to determine the equilibrium pair distribution function and the perturbation due to the flow. Intramolecular and near-field intermolecular hydrodynamic interactions are neglected as appropriate for so-called free draining macromolecules. The resulting bulk stress contains separate contributions from the far-field hydrodynamic interactions and the electrostatic forces. The coefficient of the O(c2) term in the viscosity which equals 0.4 in the purely hydrodynamic limit is predicted to increase dramatically with decreasing ionic strength for charged macromolecules in agreement with experimental data in the literature.