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A new free volume theory, which we named “shell-like free volume” theory, is developed for penetrant diffusivity in polymers by introducing microscopic concept of molecular collisions. Shell-like free volume is defined as the ambient free space of the penetrant molecule; it is consistent with the notion of molecular collisions, which is the microscopic origin of molecular diffusion. The microscopic notion can give physical meaning to all the parameters in the theory, and the parameters can be evaluated using the only pure-component parameters: the experimental viscosity of the solvent, the viscoelasticity of the polymer, and the molecular surface area estimated from the chemical structure using the semiempirical quantum chemical calculation. The predictive ability of the shell-like free volume theory is good for self-diffusivities of molecules with shapes from spherical to chain-like in polymer solutions over wide ranges of temperature and concentration.

An analysis of the water permeability of a molecular recognition ion gating membrane was performed. The ion gating membrane shows outstanding water permeability switching properties in response to specific ion concentrations, using an ion-responsive polymer consisting of thermosensitive poly(N-isopropylacrylamide) and crown ether moieties, grafted onto a porous substrate pore surface. To investigate the precise properties of the membrane, a polycarbonate track-etched membrane having straight pores with a narrow pore size distribution was used as the substrate, and the ion responsive polymer was grafted onto its pore surfaces. The gating property of the prepared membrane was examined as a function of temperature, specific ion concentration, and filling ratio. Estimates of pore size and dimension of the grafted polymer were obtained using the Hagen–Poiseuille equation. We found that the grafted ion-responsive polymer shows drastic dimensional changes in response to temperature and specific ion concentrations.

For the practical use of a polymer electrolyte membrane fuel cell (PEMFC), the structure optimization of the electrode is important in obtaining high performance. Usually, a perfluorosulfonic acid (PFSA) ionomer is used as a binder in the electrode for a novel hydrocarbon electrolyte membrane by many pieces of research because the optimization of hydrocarbon electrode is difficult. However, to reduce costs and the environment load of the F element, the development and the optimization of hydrocarbon electrode for hydrocarbon instead of the PFSA electrode is necessary in the end. This research focused on the adoption of sulfonated poly(arylene ether sulfone) (SPES) as an example of a hydrocarbon ionomer to the electrode and the relationships between the structure of the catalyst layer and the size (radius of gyration) of the SPES related with the molecular weight as a fundamental research for the optimization of the hydrocarbon electrode. From the aspect of the structure of the electrode, we controlled the molecular weight of the SPES in order to enlarge the three-phase boundary for the electrode reaction. We have examined the correlation of the molecular weight of SPES and catalyst utilization, and the structure change of the catalyst layer was observed. The electrode fabricated with low molecular weight SPES showed a high utilization of the catalyst and good fuel cell performance.

The processing and characterization of a novel membrane system for CO 2 separation is described. The membrane was made of lithium zirconate (Li 2 ZrO 3 ), which has a potential to react reversibly with CO 2 molecules at high temperatures. The reaction of Li 2 ZrO 3 with CO 2 essentially produced two electrolyte materials in situ. One of them, Li 2 CO 3 , is capable of carrying CO 2 , and the other, ZrO 2 , is a well-known O 2 ion conductor. This combination of selective reaction and electrolyte conduction permitted the design of a membrane system capable of selective CO 2 steady-state permeation across the membrane. Using the membrane, a separation factor of 4.9 was measured between CO 2 and CH 4 gas molecules at a temperature of 600°C. The measured separation value of 4.9 is very high compared with the Knudsen diffusion limit of 0.6 and therefore clearly supports the use of the membrane system for selective separation of CO 2 .

The reverse osmosis process needs no phase transformation during separation, and thus it has a potential in saving energy for liquid mixture separations. Application of reverse osmosis to organic liquid is limited, owing to the lower stability of polymer membranes against organic liquid. Zeolites are inorganic materials having durability against organic liquid and heat, and they show good separation ability in pervaporation. In this study, zeolite membrane was firstly applied to the reverse osmosis process. Zeolite A membrane, having thickness around 5 μm, showed 0.44 rejection from 10wt% ethanol water mixture. The membrane was stable to applied pressures up to 50 kgf cm–2.