Abstract
Nanocomposite type hydrogels (NC gels) were synthesized by in-situ free-radical polymerization of N-substituted acrylamides in the presence of various inorganic clays in water. It was confirmed that, NC gels, formed without using organic crosslinker, exhibited extraordinarily good mechanical properties due to the formation of organic (polymer) / inorganic (clay) networks, in comparison with conventional organic crosslinked hydrogels (OR gels) or gel-like materials prepared from linear polymers (LR gels).The tensile strengths and fracture energies of NC gels were observed to be approximately 10 and 500 times those of corresponding OR gels. NC gels prepared using synthetic swollen hectorites with slightly different compositions exhibited reproducibly good mechanical properties. Also, it was found that the modification of clay by, for example, fluorine substitution and/or the addition of a dispersant such as sodium pyrophosphate had large effect on the mechanical properties of the resulting NC gels. The modulus and strength decreased while elongating to break increased by introducing fluorine into the clay and incorporating the dispersing agent. Furthermore, in the case of clay which did not swell in water, the mechanical properties of the NC gel obtained became very poor and close to those of LR gels. The change in stress-strain curves using different clays and modifications was discussed in terms of the change in crosslinking density in the organic/inorganic network structure model.
