Redistribution of low-molecular-mass acid between polyelectrolyte hydrogel and solution

The behavior of hydrogels based on polyacrylic acid with different degree of charging in hydrochloric acid solutions was studied. Redistribution of low-molecular-mass acid in the hydrogel-solution system and changes in the gel volume were examined. Depending on the ratio between the number of Na + and H + ions in the system, either binding of hydrogen ions or an increase in acid concentration outside the hydrogel was observed. A simple model based on the Donnan theory, which took into account dissociation of carboxyl groups attached to the polymer network, provides a good description of experimental evidence.