Effects of Polymer Concentration on Structure and Properties of Zwitterionic Nanocomposite Gels

Zwitterionic nanocomposite gels (Zw-NC gels) composed of a zwitterionic sulfobetaine copolymer and inorganic clay (hectorite) are synthesized through the in situ free-radical copolymerization of N,N-dimethyl(acrylamidopropyl)ammonium propanesulfonate (90 mol%) and N,N-dimethylacrylamide (10 mol%) with exfoliated clay platelets in an aqueous medium. The effects of polymer concentration (C-p) on the dynamic viscoelasticity, tensile mechanical properties, transparency, and the thermosensitivity with the upper critical solution temperature (UCST) of the Zw-NC gels are investigated in the range C-p = 26-260 g L-1 and are compared with those of chemically cross-linked zwitterionic gels. All the mechanical and thermosensitive properties strongly change depending on the type of network and C-p. The C-p-induced changes in the polymer-clay structure of the Zw-NC gel are discussed based on the mechanical, optical, and thermosensitive properties, and on transmission electron microscopy and X-ray diffraction measurements. image