The process of forming the unique organic/inorganic network structure of nanocomposite hydrogels (NC gels) was studied through changes in viscosity, optical transparency, X-ray diffraction, and mechanical properties. It was concluded that, during the preparation of the initial reaction solutions, a specific solution structure was formed from monomer (NIPA) and clay, where NIPA prevents gel formation of clay itself, and initiator (KPS) is located near the clay surface through ionic interactions. In subsequent in-situ free-radical polymerization, it was observed that the viscosity increased markedly during NC gel syntheses and in a manner similar to that in OR gel syntheses. Also, NC gels with different polymer contents exhibit characteristic two-step changes in the stress−strain curves, which correspond to the primary network formation and subsequent increase of cross-link density. These are because the polymerization proceeds on the clay particles which are relatively immobile, and clay platelets act as effective multifunctional cross-linking agents (plane cross-link). Then, it was proposed that clay−brush particles, consisting of exfoliated clay platelets with numbers of polymer chains grafted to their surfaces, were formed in the very early stage of polymerization, at around 7% of monomer conversion. Novel decreases in transparency were observed corresponding to the formation of clay−brush particles, but transparency recovered on further polymerization. Clay−brush particle formation was confirmed by XRD measurements on dried NC gels prepared using small amounts of monomer. Thus, a mechanism for forming the unique organic/inorganic network structure, including the formation of clay−brush particles in the synthetic pathway, is proposed. Furthermore, it was found that NC gels with excellent mechanical properties and structural homogeneity could not be prepared using other methods such as mixing clay and polymer solutions or by in-situ polymerization in the presence of the other inorganic nanoparticles instead of clay. These results indicate that the formation of organic/inorganic network structures in NC gels is highly specific and only realized by in-situ free-radical polymerization in the presence of clay.

In the last two decades, polymer-clay nanocomposites (P/C-NCs) have been extensively investigated as advanced composite materials. 1 Conventional P/C-NCs consist of exfoliated clay sheets and thermoplastic or thermosetting polymers, such as nylon 6, polypropylene, polyurethane, or epoxy resin. It was reported that P/C-NCs show remarkable improvements compared with virgin polymers in mechanical (e.g., modulus), thermo-mechanical (e.g., heat distortion temperature), surface (e.g., gas-barrier), and thermal (e.g., nonflammability) properties by the inclusion of small amounts of clay sheets. 2 These P/C-NCs were generally prepared by using organophilic clay pre-modified by an alkylammonium surfactant. In most cases, P/C-NCs include 1-5 wt %, and less than 10 wt %, of clay. P/C-NCs with higher clay contents were not satisfactory in use because of difficulties in both preparing uniform P/C-NCs and their molding. Also, it was reported that a porous (polypropylene/ organophilic clay) P/C-NC could be prepared using supercritical CO 2 as porogen, 3 and that the average pore size was reduced from 153 to 93 µm by incorporating 4 wt % clay.We recently developed a novel series of nanocomposite hydrogels (NC gels) with unique organic (polymer)/inorganic (clay) network structures. 4 These NC gels were obtained by in situ free-radical polymerization of N-substituted acrylamide derivatives in the presence of exfoliated inorganic clay in aqueous media. In the network, neighboring clay sheets are linked by large numbers of long, flexible polymer chains. Each clay sheet acts as a super-multifunctional cross-linking agent. Here, the most probable interaction between polymer and clay, which is not covalent bonding, is a hydrogen bonding interaction, although an ionic interaction involving initiator (potassium peroxodisulfate) fragments might also contribute. Because of their unique network structure, NC gels simultaneously exhibit extraordinarily tough mechanical properties (high elongation and strength), high transparency (structural homogeneity), high swelling ratio, and excellent thermo-responsive characteristics (gel volume and transparency transitions). 4-6 It was also found that transparent P/CNCs with high contents of exfoliated clay were readily obtained by drying the NC gels. 5,6 Here, we report the preparation of porous nanocomposite materials composed of poly(N-isopropyl acrylamide) (PNIPA) and clay by freezedrying NC gels. The resulting porous nanocomposites exhibit characteristic layered morphologies with controlled porosities.NC gels, as monoliths, were synthesized and analyzed by the same procedures as reported previously. 5 Standard uniform aqueous solutions containing clay (synthetic hectorite [Mg 5.34 Li 0.66 Si 8 O 20 (OH) 4 ]Na 0.66 , 3.31 g), monomer (Nisopropyl acrylamide, 10 g), catalyst (N,N,N′,N′-tetramethylethylenediamine, 80 µL), initiator (potassium peroxodisulfate, 0.1 g), and water (100 g) were first prepared at 1°C. A standard solution was clay/monomer weight ratio ) 0.33, water content ) 88.3 wt %. The s...

Hydrogen of hydrogen station for FCV is usually produced by the reforming reaction, followed by the water gas shift reaction. The reformed gas contains a large amount of CO 2 , and this decreases the power efficiency although it does not influence the PEFC performance. The CO 2 removal technology from the reformed gas is an important factor to improve the FCV performance. We developed a membrane for selective CO 2 separation containing carbonate salt as a CO 2 carrier. The support material of the CO 2 carrier for a selective CO 2 separation membrane should have water solubility, mechanical strength and heat resistance. We evaluated three support materials, PVA, AQN and NDP. The PVA membrane was broken at high temperature region though it showed good CO 2 permeance at low temperature region. The AQN membrane had low CO 2 permeance in all temperature regions. Although the NDP membrane had CO 2 permeance at high temperature region, it should be improved further to increase the CO 2 permeance.

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