Electroviscous effect on the rheology of a dilute solution of flexible polyelectrolytes in extensional flow

This paper presents the first mathematical formulation for the effect of do uble layer deformation on the conformational and rheological behavior of a dilute solution of flexible polyelectrolytes. The polyelectrolyte is modele d by a charged FENE dumbbell, in which the bead centers are regarded as cha rge points, each carrying an equal effective charge, in the calculation of electrostatic interaction under the Debye-Huckel approximation. For an arbi trary linear flow, an induced electrical force on each bead associated with the double layer deformation is derived. Incorporating this force in the d iffusion equation and using a perturbation method, the configuration distri bution function of the dumbbells can be determined analytically for the cas e of an extensional flow. The resulting distribution function is then used to calculate the root-mean-square end-to-end distance. It is found that the double layer deformation leads to an increase in the average dumbbell leng th, compared to the results by ignoring this effect. The force associated w ith the charge cloud distortion increases with decreasing double layer thic kness, as opposed to the equilibrium electrical force. The stress behavior is also discussed for the cases of thin and thick double layers. (C) 2001 E lsevier Science B.V. All rights reserved.