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

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 (C-NaCl), clay concentration (C-clay), and temperature. In water, characteristic swelling-to-deswelling behavior and an abnormal increase in the degree of swelling (DS) with increasing C-clay (proportional to 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 C-NaCl and above the critical point (0.01 M), the DS increased with C-NaCl via an anti-polyelectrolyte effect of the zwitterions and decreased with increasing C-clay. The transparency also changed depending on the C-NaCl C-clay, 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. (C) 2015 Elsevier Ltd. All rights reserved.