Ionic strength, swelling dependence

In most cases, the swelling of polyelectrolyte hydrogels depends only on ionic strength of the solution but not on the size and nature of the ions [101]. Therefore, the ionic suppression curves similar to those of Fig. 2 and 3 are to some extent universal and allow to predict quantitatively the swelling of hydrogels for practically any ionic situation. 

The results are generally consistent with a broader treatment of the techniques for measuring particle swelling of carboxylic emulsion polymer latexes reported elsewhere in this Monograph (9). The broader study, which was carried out independently but concurrently, has shown that the magnitude and pH of maximum expansion depends on dilution and ionic strength. Studies of the concentration dependence in the dilute regime and more concentrated systems are underway. 

Water-soluble poly(acrylic acid)-based nanocapsules with reversible pH- and ionic strength-dependent swelling transition were prepared by Meier et al. [224], During this transition gated pores in the spherical polymer shells are opened (closed), which enables free molecular exchange between the interior of the hollow sphere and the bulk medium. This pH-switchable control of permeability can trigger release of encapsulated cargo from the polyelectrolyte spheres. 

---