Reversible Hardness Variance as a Commonly Observable Phenomenon for Various Amphoteric Gels

Abstract

Acrylamide-based amphoteric gel containing -COOH and -NH₂ can be hardened through the formation of salt-linkages, -COO^-···⁺H₃N-, which serve as columns to reinforce the gel matrix. These salt-linkages can be formed and disrupted reversibly by the control of ionic strength of bathing solution, resulting in the gel hardness variance. The same kind of salt-linkages were also found to form between immobile -SO₃H and -NH₂ both imported in acrylamide-based gels, in the form of -SO₃^-···⁺H₃N-. It was also observed a reversible formation and disruption of -SO₃^-···⁺H₃N- according to the ionic strength of bathing solution. Thus the import of both -SO₃H and -NH₂ groups in a single gel is expected to induce a reversible hardening and softening of gel matrix through the formation of salt-linkages. From this observation, it was strongly speculated that the reversible hardness variance has to be a quite common phenomenon for any type of amphoteric gel.