| Research Abstract |
Control of the network structure of polymer gel is of particular importance not only in understanding of the origin of the advanced properties of the polymer gels, but also for designing even newer types of gels. In this project, we carried out a series of structural, mechanical and functional investigations for nanocomposite type hydrogel (NC gel) consisting of poly(N-isopropylacrylamide) (PNIPA) and inorganic clay (hectorite). (1) We firstly synthesized NC gels with various clay concentrations (C_<clay>), and studied the mechanism of forming unique organic / inorganic network structure during in-situ free-radical polymerization through changes in viscosity, optical transmittance, X-ray diffraction and mechanical properties. Then, we proposed the unique network formation mechanism, including the formation of clay-brush particles. Also, (2) we revealed that the mechanical properties (modulus and strength) of NC gels can be varied in a wide range, without sacrificing the ultra-high elon
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gation at break (1000%), depending on the C_<clay>. In particular, it was found that NC gels exhibit the extraordinarily high fracture energy (up to 3000 times that of conventional chemically-crosslinked hydrogel), and that the strength reached to 3 MPa by subsequent elongation treatment. Furthermore, we found a number of important properties of NC gels, such as (3) appearance of optical anisotropy in NC gels at above critical C_<clay>, (4) reversible force generation as a result of the coil-to-globule transition of PNIPA chains in response to cycling the temperature across the lower critical solution temperature, (5) total control of the coil-to-globule transition by incorporation of clay nano-particles, (6) the formation of unique porous morphologies with a three-layered structure in the freeze-dried state, (7) the characteristic sliding frictional behaviors with remarkable changes in the coefficient of friction at the surface of NC gels, (8) biocompatibility including implantation and antithrombogenicity, etc. Thus, many interesting and important characteristics of NC gels are clarified through this project. Less
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