Ion Conductivity of Polyelectrolyte Hydrogels with Varying Compositions

Ion transport in polyelectrolyte (PE) hydrogels is governed by a complex interplay between charge distribution, network architecture, and ionic interactions; however, the role of hydrogel composition in ion conductivity remains elusive. Here, we report the results of an experimental and simulation study of ion conductivity and ion mobility in PE gels formed from random copolymers containing charged and charge-neutral repeat units. For anionic or cationic copolymers with H⁺ or Cl^- counterions, respectively, control over charge concentration and pore size was achieved by systematically varying the fraction of charged monomers and the cross-linking density of the hydrogel. We show that the dependence of ion mobility on charge concentration becomes stronger in hydrogels formed by the copolymers with a reduced fraction of charged repeat units. Moreover, the variation in the mobility of H⁺ ions is more sensitive to hydrogel composition than that of the Cl^- ions, thus highlighting ion-specific effects. The experimental results are in agreement with the simulation. These findings provide insight into the mechanisms of ion transport in compositionally heterogeneous PE networks and offer design principles for creating functional biomimetic hydrogels with tunable ionic conductivity.