Dilute Solution Viscoelasticity of Simple Ionic Polymers—A Theory for Charged Bead-Spring Models

Abstract

As part of a comprehensive study of the viscoelastic properties of ionic polymers, a theoretical investigation of the dilute solution viscoelasticity of simple ionic polymers was undertaken. The bead‐spring model of Rouse was modified to include electrostatic charges in the beads. For the two simplest cases of this model (the elastic dumbbell and the three bead‐two spring assembly), the diffusion equation for the distribution function of bead separation in shearing flow was formulated. Numerical solutions were obtained for a range of values of the charge and spring parameters. The values were chosen to correspond to real polymers for which the charged bead‐spring model would be appropriate, such as linear dicarboxylic acids and polymeric zwitterions for the dumbbell, and linear triacids for the three bead model. It was found that the effect of ions can be described by simple multiplicative shifts in the relaxation times of the uncharged material. For like‐charged dumbbells, both the relaxation time and the intrinsic viscosity increase; for oppositely‐charged dumbbells, both of these functions decrease in value. For the three bead model, the intrinsic viscosity and both of the relaxation times increase. In addition, the ratio of the two relaxation times increases, indicating a broadening in the distribution of relaxation times.