Search

Nanofibers have unique functionalities based on their nanoscaled cross‐section, high specific surface area, and high molecular orientation inside the fibers. These functionalities can be improved by controlling their diameter, surface and internal structures. The introduction of ion‐exchange sites on the surface and/or inside the nanofibers provides novel high‐functional ion‐exchangers with high surface areas, high ion‐exchange and adsorption capacities, and high ionic conductivities. The present review highlights the fundamental aspects of ion‐exchange nanofibers (i.e. their size‐dependent unique properties and production methods) and their recent advances in the environment and energy applications (i.e. separation/purification processes and fuel cells). © 2018 Society of Chemical Industry

A pressure-retarded osmosis (PRO) power generation system is a hydroelectric power system which utilizes permeation flow through a semipermeable membrane. Permeation flow is generated by the potential energy of the salinity difference between sea water and fresh water. Since the cost of the membrane is high, the permeation performance of the membrane must be improved in order to realize PRO systems. We have investigated reverse osmosis (RO) membrane products as semipermeable membranes and measured the permeation volume of a few products. The generation power per unit membrane area calculated from the permeation volume is about 0.62 W/m2. But as a result of our improvements (greater salt water volume, spacers for fresh water channel with the function of discharging concentrated salinity, extralow-pressure type of membrane, washing the support layer of membrane when the generation power falls by half) the generated power may be 2.43 W/m2. Then the power system cost would be about 4.1 million yen/kW. In addition, if the support layer of the membrane is made thinner and a PRO system is applied to equipment where pumping power for another purpose is available (wastewater treatment plants located at the seaside, thermal and nuclear power plants, sea water desalination plants), the generated power may be increased. These improvements may enable PRO systems to be realized at a cost close to that of photovoltaic power systems. 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 173(2): 8–20, 2010; Published online in Wiley InterScience (www.interscience. wiley.com). DOI 10.1002/eej.21000

The in situ optical absorption and fluorescence of poly(3-octylthiophene) (POT) upon electrochemical doping were studied. Fluorescence from the undoped POT was observed in the acetonitrile electrolyte. It was quenched by the electrochemical doping. The effect of a dopant molecule on the intensity change of the fluorescence is 7.5 times greater than the one for the optical absorption. Thus, the fluorescence quantum yield decreased after electrochemical doping. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3111–3115, 2006

The current-voltage curves of a composite bipolar membrane (CBM) were experimentally measured by inserting the thin poly(acrylonitrile) (PAN) membrane between cation- and anion-exchange membranes for water and methanol solutions. In each solution system, 0.05 mol/L LiCl was used as the electrolyte. The measured results show that the thin PAN membranes enhanced the water- and methanol-splitting effect. This phenomenon can be explained by the protonation-deprotonation reactions occurring between the functional group of PAN (-C≡N, cyano) and the water or methanol molecules in the intermediate region of the CBM. The effect of niobium alloy (Nb 3 Ga), fullerene (C 60 ) and titanium oxide (TiO 2 ) existing in the intermediate region of the CBM was also experimentally examined in this study. It was found that the effect of these compounds on water or methanol-splitting was not obvious.

Gas permeabilities across poly(chloro-p-xylylene) (parylene C) films are measured with different thicknesses of 20.2, 10.0, 8.9, 4.6, 3.4, and 1.0 μm. Measurements were carried out below 1 atm and between 10 and 80°C, which are under the glass transition temperature. The temperature and pressure dependencies of the permeability and the apparent diffusion coefficients were measured. If the membrane thickness is larger than 8 μ, the gas-transport mechanism is solution–diffusion, which implies that it is pinhole-free, because the pressure dependency of the permeability cannot be found and the apparent activation energy of permeation and diffusion are observed. If the membrane thickness is less than 8 μ, the gas transport mechanism is pore flow combined with solution–diffusion flow because gas may penetrate both the porous area and the polymer matrix. The thinner the membrane, the higher is the permeability coefficient, since the diameter and number of pores increase with decrease of the membrane thickness. The gas permeability coefficient has different values at the same pressure or temperature. As this film is in the glassy state, it should be explained using the average ordering parameter (ξ), which is a function of temperature, pressure, gas concentration, and time. © 1994 John Wiley & Sons, Inc.

A membrane, which has positively charged groups in the polymer main chain, was prepared from polyethylenimine by crosslinking and successive alkylation. Dibromoalkane was used as a crosslinking agent. The crosslinked membrane was alkylated using methyl iodide under several conditions. Elemental and ICP emission analyses were introduced to measure the rates of alkylation and quaternization. From the membrane potential measurement, the effective charge density was estimated. The highest value was about 1.0 M, which was obtained by a prolonged alkylation time. This value was larger than that of some commercial ion exchange membranes. The effective charge density, which was obtained by the last alkylation procedure, was 10 times larger than that of the former one, though the rate of quaternizing increased by less than a factor of two. This implies that the activity constant in the membrane increased when the charge density is increased. © 1993 John Wiley & Sons, Inc.

The tert.-butyl substitution in title compound (Ib) realizes standing arrangement of the molecules and consequently good OFET (organic field-effect transistor) performance.

Effects of carbon filler on the sorption and diffusion of carbon dioxide in natural rubber and in styrene-butadiene rubber have been studied. Sorption isotherms conform to Henry's law in unfilled rubber and to Langmuir's law in carbon black. The isotherms in filled rubber exhibit a combination of the two sorption modes. The Henry's law solubility parameter kD increases with carbon filler content; the Langmuir saturation constant C′A initially is constant with filler level, but then decreases abruptly when carbon particles begin to aggregate. The diffusion coefficient decreases with increasing filler content, presumably owing to geometric effects and to polymer chain immobilization in the interfacial regions.

The mechanical properties of gelatin films were studied in relation to the effect of water, and compared with those of collagen films. The S-shaped sorption isotherm was separated into an adsorption curve C1 and dissolution curve C2. From the C2 curve, the interaction parameter χ1 of Flory–Huggins' equation was calculated. The χ1 of gelatin were larger than those of collagen at low relative humidities (RH), while they coincided with each other at high RH. It was found that a composite curve was made by shifting stress relaxation curves obtained at different humidities along the log time axis. The shift factor for the formation of the composite curve was analyzed by Fujita–Kishimoto's equation, which was based on the free volume theory. The parameter β, which expressed the extent of the contribution of sorbed water to the increase in the free volume of the system, was 0.05 in the range of C2 from 0 to 0.08 (0–65% RH). This value was much smaller than 0.16 for collagen. The value was 0.16 in the range of C2 higher than 0.08, which was equal to that of the collagen. Dynamic shear modulus G′, loss modulus G″, and tan δ were determined as functions of RH. The gelatin film extended more than 100% at 73% RH under the very small stress of about 107 dyn/cm2. This corresponds to the region where β changes from 0.05 to 0.16, although such a phenomenon was not observed in the collagen film. The wide-angle X-ray pattern of extended gelatin was similar to that of renatured collagen fiber.

The pore size for a fine porous freeze-dried cellulose acetate membrane was evaluated by gas separation methods, where the Present–deBethune equation was applied. Separation coefficients were referred to the calculated value for each pore size from this equation. Nuclepore, Millipore VS, and Millipore VC, whose pore sizes were already known by bubble point method, were tested for this method. Pore diameters for this cellulose acetate membrane, thus determined, were about 25 and 40 A from Ar–Kr and N2–Kr separation systems, respectively, which agreed well with the results from electron microscope (50 A) and N2 gas permeability (50 A). However, it is impossible to apply this method to He gas separation, since He gas permeability is higher than the expected value as Knudsen flow, which indicates that some channels are existing in this membrane, where He gas is more permeable than the other gases.

Permeabilities of He, N2, O2, Ar, and CO2 in stretched hard-elastic polypropylene film exhibiting extraordinarily high elasticity were measured as functions of temperature, pressure, and extension ratio. The permeability decreases slightly for strains of 10% or less, increases abruptly for strains from 15% to 30%, and then increases gradually for strains up to 100%. In recovery from extension, changes in permeability are similar to those in extension. The gas permeation mechanism is of the solution-diffusion type for extensions less than 15%. Above 15% extension, the mechanism involves permeation through voids created during deformation. The apparent mean pore size, estimated from the gas permeation, is very large at comparatively small extensions, and decreases with increasing extension. The change in specific volume accompanying extension of the sample indicates that only a very small fraction of the voids are interconnected to form channels that traverse the thickness of the film.

A Freeze-dried cellulose acetate membrane with high permeability and high separation factor was prepared. In the successive membrance process, the heat treatment temperature was 80°C for constant period of 10 min, acetone evaporation time was between 4 and 6 min, and the membrane was fixed during drying to prevent shrinkage. Gas permeabilities for such a membrane were inversely proportional to the square root of molecular weight, suggesting that the mechanism of gas flow through this membrane was Knudsen flow. Separation factors for H2He, ArKr, N2Kr, HeNe, H2Ne, HeAr, ArH2, HeKr, ArHe, and HeH2 were measured. These factors were higher than those of membranes reported already. Separation efficiency largely depended upon the combination of mixed gases. The combination of two atom molecules and one atom molecule lowered the separation efficiency compared with the combination of one atom molecule and one atom molecule.