Ion-specific swelling of hydrophilic polymer gels

Ion-specific swelling of poly(allylamine) (PAlAm) gel and poly(vinyl alcohol) (PVA) gel was investigated in various aqueous salt solutions. Both the gels slightly swelled in the presence of small cations (e.g. Li+) and markedly deswelled in the presence of small anions (e.g. F−), in a similar way as previously found for poly(N-vinylpyrrolidone) (PVP) gel. However, a significant difference was observed among the gels swollen in aqueous NaCl system; only PVA gel showed a remarkable deswelling at the higher NaCl concentration region. These ion-specific swelling behaviors were interpreted in terms of ion effects on the hydrogen-bonding hydration to the pertinent polar groups.