A charged finitely extensible dumbbell model: Explaining rheology of dilute polyelectrolyte solutions
Abstract
A robust nonNewtonian fluid model of dilute polyelectrolyte solutions is derived from kinetic theory arguments. Polyelectrolyte molecules are modeled as finitely elongated nonlinear elastic dumbbells, where effective charges (interacting through a simple Coulomb force) are added to the beads in order to model the repulsion between the charged sections of polyelectrolyte chains. It is shown that the relative strength of this repulsion is regulated by the electrictoelastic energy ratio, E, which is one of the key parameters of the model. In particular, E accounts for the intrinsic rigidity of polyelectrolyte molecules and can be used to explain the impact of solvent salinity on polyelectrolyte rheology. With two preaveraging approximations, the constitutive equations of the resulting fluid model are formulated in closed form. Material functions predicted by the model for steady shear flow, steady extensional flow, smallamplitude oscillatory shear flow, and startup and cessation of steady shear flow are obtained and investigated using a combination of analytical and numerical methods. In particular, it is shown how these material functions depend on E. The two limiting cases of the model—uncharged dumbbells (E = 0) and rigid dumbbells (E → ∞)—are included in the analysis. It is found that despite its simplicity, the model predicts most of the experimentally observed rheological features of polyelectrolyte solutions.
 Publication:

Physics of Fluids
 Pub Date:
 June 2020
 DOI:
 10.1063/5.0008321
 arXiv:
 arXiv:1907.00003
 Bibcode:
 2020PhFl...32f3101S
 Keywords:

 Condensed Matter  Soft Condensed Matter;
 Physics  Fluid Dynamics
 EPrint:
 36 pages, 8 figures