Control of nanophases in polyelectrolyte gels by salt addition

We propose a continuum theory to describe the influence of salt on the phase segregation behavior of polyelectrolyte gels. The equilibrium phase behavior is determined by the steady state solution of time-dependent Ginzburg-Landau evolution equations using an efficient spectral technique. Numerical solutions of a model system with density inhomogeneities in one direction show a transition between no phase separation (swollen gel), nanophase segregation (lamellar nanostructures), and macrophase separation (collapsed gel); as the salt concentration increases. The wavelength of nanophases increases with the salt concentration and the resulting parameter regime of nanophases depends strongly on the salt concentration. We augment the numerical solutions with a weakly nonlinear analysis, that describes primary consequences of salt addition and highlights the effect of nonlinearities on the phase segregation behavior.