Equilibrium swelling of a polyampholytic pH-sensitive hydrogel.

Immersed in an ionic solution, a network of polyampholytic polyelectrolyte imbibes the solution and swells, resulting in a polyampholytic p H-sensitive hydrogel, which can respond to changes in the surrounding environmental p H. This paper formulates a continuum field theory for polyampholytic p H-sensitive hydrogels by considering the reaction of hydrogen ions with hydroxide ions, which has been ignored in our previous paper (H.X. Yan, B. Jin, Eur. Phys. J. E 35, 36 (2012)). Comparison with experimental data shows that the proposed continuum field theory, by considering that the reaction of hydrogen ions with hydroxide ions would be more reasonable, can not only give a good qualitative but also a good quantitative prediction of the dependence of swelling on p H and crosslinker. The theory is then applied to study the influence of chain entanglements, salt concentration, uniaxial tension and geometric constraint on mechanical behavior of polyampholytic p H-sensitive hydrogels.