Formation Mechanism and its Control of Organic / Inorganic Network in Nanocomposite Gel

控制聚合物凝胶的网络结构不仅对了解聚合物凝胶先进性能的起源，而且对设计更新型的凝胶具有特别重要的意义。在本项目中，我们对由聚n -异丙基丙烯酰胺（PNIPA）和无机粘土（hectorite）组成的纳米复合型水凝胶（NC gel）进行了一系列的结构、力学和功能研究。(1)我们首先合成了不同粘土浓度（C_<clay>）的NC凝胶，并通过粘度、透过率、x射线衍射和力学性能的变化研究了原位自由基聚合过程中形成独特的有机/无机网络结构的机理。然后，我们提出了独特的网络形成机制，包括粘土刷颗粒的形成。此外，(2)我们发现NC凝胶的力学性能（模量和强度）可以在很宽的范围内变化，而不牺牲超高的断裂速率（1000%），这取决于C_<粘土>。特别是，研究发现，NC凝胶具有极高的断裂能（高达常规化学交联水凝胶的3000倍），并且经过后续延伸处理后，其强度达到3mpa。此外，我们还发现了NC凝胶的一些重要性质，如(3)在临界温度C_<粘土>以上时，NC凝胶中的光学各向异性的出现；(4)在较低的临界溶液温度上循环，PNIPA链的线圈到球的转变会产生可逆力；(5)粘土纳米颗粒的加入可以完全控制线圈到球的转变。(6)在冻干状态下形成具有三层结构的独特多孔形态；(7)NC凝胶表面摩擦系数发生显著变化的特有滑动摩擦行为；(8)生物相容性，包括植入性和抗血栓性等。因此，通过该项目阐明了NC凝胶的许多有趣和重要的特性。少

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 … More 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