In this study we examine the volumetric properties of such polyelectrolyte gels in relation to the progressive substitution of monovalent counterions by divalent counterions as the gels are equilibrated in solvents of different dielectric qualities. We compare the results of coarse-grained molecular dynamics simulations of polyelectrolyte gels with experimental measurements on polyacrylate and DNA gels. The simulations show that under equilibrium conditions there is an approximate cancelation between the electrostatic and counterion excluded-volume contributions to the osmotic pressure in the gel-solvent system.Based on these results, we show and explain that a modified form of the Flory Huggins model for neutral gels, which accounts for neither electrostatic effects nor counterion excluded-volume effects, fits both experimental and simulated data for polyelectrolyte gels.Molecular simulations also reveal that the condensation of divalent counterions onto the polyelectrolyte network backbone occurs preferentiallyover that of monovalent counterions.
Citation: Condensed Matter Physics
Pub Type: Journals
dielectric constant, DNA and polyacrylate gels, elasticity, monovalent and divalent counterions, polyelectrolyte gels, spatial extent of counterion cloud