Tunable Optical and Swelling/Deswelling Properties Associated with Control of the Coil-to-Globule Transition of Poly(N-isopropylacrylamide) in Polymer−Clay Nanocomposite Gels

Abstract

Polymer−clay nanocomposite gels (NC gels) consisting of poly(N-isopropylacrylamide) (PNIPA) and inorganic clay (hectorite) were investigated in terms of their optical and swelling/deswelling properties. Depending on the clay concentration (Cclay), NC gels exhibit unique changes in optical transmittance, optical anisotropy, and swelling/deswelling behaviors, all of which were distinct from those of chemically cross-linked hydrogels (OR gels). The optical transparency and its temperature-induced change differed greatly between NC and OR gels. The decrease in transmittance associated with the coil-to-globule transition of PNIPA occurred at higher temperatures than the normal transition temperature in NC gels as the clay concentration increased. On the assumption of the uniform and random dispersion of exfoliated clay platelets, the critical Cclay (C*clay) for spontaneous clay aggregation (layer stacking) in NC gels was calculated to be 10 × 10-2 mol/L H2O. C*clay was consistent with the experimental results,...