Stimuli-responsive polyelectrolyte gels and the role of ion and polymer solvation*

Polyelectrolyte gels are essential components of living systems, since biological tissues are largely composed of polyelectrolyte gels providing a medium for the transport of ions and molecules more easily and effectively while at the same time providing structural integrity. The challenge of modeling the influence of solvation and ion partition on the swelling of gels is due to the coupling between the polyelectrolyte chain configurations and the spatial distribution of the ionic species in solution. We perform molecular dynamics simulations of a minimal model of a polyelectrolyte nanogel particle in solution with an explicit solvent and ions, where the relative strength of dispersion interactions between the solvent and the charged species defines the solvent quality and the position of the ion along the Hofmeister series. Our findings demonstrate that the solvent plays a crucial role in gel swelling and the sensitivity of swelling to the addition of salt and the ion partitioning between the gel and the surrounding solution. Overall, our findings provide a guideline for the development of a more predictive theory of the thermodynamic and transport properties of these complex systems.