Diffusive Trends\nin Concentrated Oppositely-Charged\nPolyelectrolyte Solutions and Onset of Glassy Dynamics

We utilize single particle tracking studies to investigate\nthe\ndiffusion of polylysine through concentrated matrices of cationic\npolylysine and anionic polyglutamic acid with no added salts. These\nstudies show that diffusivity has a strong apparently exponential\ndependence on concentration in crowded systems that does not appear\nto be a function of the charge sign. These trends are consistent in\nboth single-phase systems prepared at concentrated conditions and\npolymer-rich coacervate phases formed from dilute phase-separating\nsystems. The likely origin of this behavior is the onset of glassy\ndynamics spurred by a decrease in plasticization by water and the\nlarge excluded volume associated with charge-bearing species. This\neffect can be contextualized through free volume-based theories such\nas the Vrentas–Duda model. Overall, we obtain dynamic behavior\nthat is distinctly different from behavior observed in more dilute\nsystems and warrants further investigation.