Repulsive and attractive depletion forces mediated by nonadsorbing polyelectrolytes in the Donnan limit

In mixtures of colloids and nonadsorbing polyelectrolytes, a Donnan potential arises across the region between surfaces that are depleted polyelectrolyte rest system. This tends to shift density profile towards colloidal surface leads local accumulation polyelectrolytes. We derive zero-field theory for disjoining pressure two parallel flat plates. Polyelectrolyte is allowed enter confined interplate at cost conformational free energy penalty. The resulting shows crossover repulsive regime when separation gets smaller than size chain, followed by an attractive part. find quantitative match model self-consistent field computations take into account full Poisson-Boltzmann electrostatics.