Swelling-induced birefringence of a polyelectrolyte gel strongly interacting with metal ions

The swelling behavior of a polyelectrolyte gel in aqueous salt solutions is studied in the case where metal ions are binding with polyions, forming insoluble compounds. The hydrogel swelling and contraction in such solutions and the metal ion penetration inside the network are monitored by polarizing optical microscopy. The growth of an insoluble layer on the surface of the gel particle is accompanied by the formation of a birefringent core. Changes of the thickness of the birefringent layer with time and the dependence of the birefringence on salt concentration are discussed.