Simulation of nonlinear shear rheology of dilute salt-free polyelectrolyte solutions

Abstract

Brownian dynamics simulations are used to conduct a systematic analysis of the nonlinear shear rheology of dilute polyelectrolyte solutions, exploring its relationship to shear rate, Bjerrum length, and concentration. A simple coarse-grained bead-spring chain model that incorporates explicit counterions is used. It is found that the polyelectrolyte chains exhibit a shear thinning behavior at high shear rate (as characterized by bead Peclet number Pe) that is independent of the electrostatic strength due to the stripping of ions from close proximity to the chain caused by the flow. In contrast, at low values of Pe, the viscosity increases monotonically with increasing Bjerrum length over the range studied here, in contrast to the nonmonotonic trend displayed by the chain size. Furthermore, at fixed Bjerrum length, the reduced viscosity increases monotonically with concentration. The mechanism underlying these observations is essentially the primary electroviscous effect; the ion cloud surrounding a polyelectrolyte chain deforms in flow, causing a significant increase in viscosity as concentration increases. Finally, the authors have also considered the role of hydrodynamic interactions in these simulations, finding that for low concentration studies in shear flow, these do not qualitatively affect the results.

Some Physicochemical and Rheological Properties of Zedo (Farsi) Gum Exudates from Amygdalus scoparia

“…The presence of charged groups along the backbone of polyelectrolytes (polymers containing ionisable groups) plays a significant role in both the static structure and the dynamic behaviour of such systems (13). Coil expansion is one of the ways in which the unusual nature of polyelectrolytes affects the properties of the systems.…”

Hydrodynamic effects on the translocation rate of a polymer through a pore

“…51,76 For example, for a 420 m DNA N s = 200 and n k = 3960 resulting in a molecule with R g = 2.723 m and ͑k B T / H͒ 1/2 = 3.85 m, a snapshot of this molecule and the corresponding channel-pore geometry is illustrated in Fig. 7.…”

Influence of shear on globule formation in dilute solutions of flexible polymers

“…In the gradient direction of shear, Lees-Edwards boundary conditions were applied. 35,41 The simulation box was taken such that in the flow direction L box ≥ N K l, and in the gradient and neutral directions W box ≥ 2R g,θ , where R g,θ is the theta solvent radius of gyration of the polymer. To eliminate any bias due to use of periodic boundary conditions in the flow direction, care was taken to ensure that L box was long enough that the diffusion time for particles to move across the width t D = ζW 2 box /(2k B T) was less than the time scale specified by maximum velocity of the particle t v = 2L/(γW box ).…”

“…31 To capture the flow induced changes in the interactions between segments of a polymer, simulations of polymer beads interacting with co-and counter-ion beads in an implicit solvent can be used. [33][34][35] But, with this method it is computationally expensive to model long polymers in the presence of salt. In order to study flow behavior of long linear polymers interacting with nanoparticles, proteins, and other small molecules in a simple model, we have examined a dilute solution of polymer and colloids with attractions in the presence of salt.…”