Swelling/deswelling behavior of zwitterionic nanocomposite gels consisting of sulfobetaine polymer–clay networks

Abstract

The swelling and thermosensitive behaviors of zwitterionic nanocomposite gels (Zw-NC gels) consisting of sulfobetaine polymer–exfoliated clay networks were investigated in water and aqueous NaCl solutions and compared with those of physically and chemically crosslinked zwitterionic gels and non-zwitterionic NC gels. Zw-NC gels showed different swelling behavior that was strongly dependent on the salt concentration (CNaCl), clay concentration (Cclay), and temperature. In water, characteristic swelling-to-deswelling behavior and an abnormal increase in the degree of swelling (DS) with increasing Cclay (∝ crosslink density) were observed. These behaviors were in stark contrast to those obtained with other types of zwitterionic gels. In NaCl solutions, spontaneous deswelling disappeared within small CNaCl, and above the critical point (0.01M), the DS increased with CNaCl via an anti-polyelectrolyte effect of the zwitterions and decreased with increasing Cclay. The transparency also changed depending on the CNaCl, Cclay, swelling time, and thermosensitivity of the sulfobetaine polymer. These swelling behaviors and transparency changes of Zw-NC gels were explained by the combined effects of the zwitterionic polymers (anti-polyelectrolyte), ionic clay (polyelectrolyte), and clay as a crosslinker.