Polymer and solution ion shielding in polyampholytic hydrogels

This study has examined balanced and unbalanced polyampholyte hydrogel swelling transitions as a function of total polymer ion and bath salt concentration. The total polymer ion concentration ranged from 0 to 1.4 M and the bath salt concentration from 1 mu M to 1 M. Polyampholyte swelling transitions were studied experimentally using hydrogels with varying proportions of acryl-amido methyl propylsulfonic acid (AMPS-H), methacryl-amido propyl trimethyl ammonium chloride (MAPTA-Cl), and dimethyl acrylamide (DMAAm). The equilibrium swelling has been treated analytically using a modified Flory-Huggins model with ionic corrections which incorporate ion excluded volume effects. We have obtained qualitative agreement between our theory and experimental results and have discussed the limitations of our model. (C) 1998 Elsevier Science Ltd. All rights reserved.