Ion-specific swelling behavior of poly(ethylene oxide) gel and the correlation to the intrinsic viscosity of the polymer in salt solutions

The swelling behavior of a poly(ethylene oxide) (PEO) gel in solutions of various salts was investigated for the 0-2 mol dm(-3) region. The gel deswelled in solutions of sodium salts, but the ion specificity for anions was not clearly observed. The gel swelled in solutions containing strongly hydrated cations and the degree of swelling of the gel at 2 mol dm(-3) was in the following orders: CsCl less than or equal to KCl < NaCl < LiCl and BaCl2 < SrCl2 < CaCl2 < MgCl2. These results were interpreted in terms of interactions between the polymer and the ions through the hydration layers of the cations. The dimensions of PEO estimated from the results of the intrinsic viscosity of PEO in salt solutions were in accordance with this interpretation. Comparison of the swelling behavior of the PEO gel and that of a poly(vinyl alcohol) gel revealed the large difference in the effect of anions.