Electroviscous effect of rodlike polyelectrolytes in strong flow

Primary electroviscous effect of a dilute solution of rodlike polyelectroly tes subject to a strong shear flow is investigated theoretically. A linear charge distribution along the macromolecule is assumed in this study. Also the Hartmann number and the ion Peclet number are assumed small so that the electrical body force gives small perturbation to the imposed flow, and th e double layer deviates slightly from its equilibrium state. The distortion of the double layer not only gives rise to electrical stresses but also mo difies the orientation distribution of the macromolecules, leading to an in direct contribution to the stress. This modification was treated as small p erturbations to the orientation distribution of uncharged rods for weak and moderate flows in the previous work. The perturbation analysis, however, b ecomes invalid for strong flows, in which the rotational Bur of the rods du e to the charge effect is comparable to their Brownian diffusion and the ad vection by the fluid in a boundary layer region near the flow direction. Ln this study, a spherical harmonic method is used to solve for the orientati on distribution of the rods by specifying the parameters associated with th e charge effect. The results show that the moments of the orientation distr ibution and the stress stemming from the electrical effect do change in str ong flow, in comparison with those obtained from a regular perturbation met hod. (C) 1999 Elsevier Science B.V. All rights reserved.