Extreme Suppression of Dynamics in Highly Concentrated Polyelectrolyte Solutions

The dynamics of charged macromolecules in highly concentrated environments are vital to natural and industrial processes, yet they remain poorly described by previous studies. While more dilute systems can be well described by single chain models such as Rouse or reptation, these predictions break down in the concentrated regime where polyelectrolyte dynamics should be driven by collective interactions. We use single particle tracking (SPT) to directly observe the diffusivity of individual polyelectrolyte chains and to measure the overall system viscosity in concentrated solutions of 30-70 wt%. These studies uncover extreme concentration dependences of D~c^-6.1 and η~c^7.2 for both dynamic properties, much stronger than theoretical predictions for both neutral polymers and polyelectrolytes. Similar trends are observed in experiments conducted at a variety of pH and counterion conditions. These restrictions in dynamics can be attributed to contributions from monomeric friction and the large effective volume of polyelectrolyte chains due to repulsive interactions. This is further explored through the framework of the Ventras-Duda free volume theory by attributing differences between neutral and charged systems to disparity in jumping unit size. Our findings are also extended to highly concentrated solutions of oppositely charged polyelectrolytes, where free volume considerations and repulsive interactions are combined with attractive forces, to determine the significance of charge sign.