Ultra high mechanical properties in nanocomposite hydarogels and total control over the coil-globular transition of PNIPA

We recently developed a novel class of nanocomposite hydrogels (NC gels) with a unique organic / inorganic network structure. The NC gels composed of poly(N-isopropyl acrylamide) (PNIPA) and clay were synthesized by in-situ free radical polymerization using initial solutions with different clay concentrations. It was found that NC gels show high transparency regardless of clay content, and that, with increasing the clay content, the tensile strength as well as the tensile modulus increased without sacrifice of elongation. All NC gels exhibit ultra-high extensibility (near 1,000%) and the fracture energy of NC20 gel could be as much as 2650 times of that of the OR gel. Effects of high clay content on the swelling and de-swelling properties were also investigated. It was concluded that the coil-globular transition of PNIPA chain was substantially controlled by existing of exfoliated clay and it was totally restricted when the clay content is over NC15.