Collapse of acrylamide‐based polyampholyte hydrogels in water

The swelling behavior of balanced acrylam- ide (AAm)-based polyampholyte hydrogels in water and in aqueous salt (NaCl) solutions was investigated. Equi- molar ratio of the ionic comonomers 4-vinylpyridine (cati- onic monomer) and acrylic acid (anionic monomer) were used together with the nonionic monomer AAm in the hydrogel preparation. The variations of the hydrogel vol- ume in response to changes in pH were measured. It was found that the hydrogels are in a collapsed state not only at the pH of the isoelectric point pHIEP but also over a wide range of pH including pHIEP. The width of the collapsed pla- teau increased and the hydrogels assumed a more compact state as the ionic group content is increased. The antipolye- lectrolyte behavior was observed along the collapsed plateau region, where the gel occupies a larger volume in salt solu- tion. The experimental swelling data were compared with the predictions of the Flory-Rehner theory of swelling equi- librium including the ideal Donnan equilibria. V C 2009 Wiley