Yasunari Maekawa

Novel vapor sensor from polymer-grafted carbon black: effects of heat-treatment and γ-ray radiation-treatment on the response of sensor material in cyclohexane vapor

Polyethylene (PE) was grafted onto carbon black surface by γ-ray radiation of the PE-adsorbed carbon black. Vapor sensor composite materials were prepared from the PE-grafted carbon black and PE as a matrix polymer. The effects of heat-treatment and γ-ray radiation-treatment on the response of the electric resistance of the sensor material against cyclohexane vapor were investigated. The heat-treatment of the composite improved the crystallinity of the matrix PE, and thus increased the responsiveness against cyclohexane vapor about five times that of the untreated one. The γ-ray radiation-treatment slightly decreased the responsiveness against cyclohexane vapor, because the γ-ray radiation-treatment induced the crosslinking of PE. On the contrary, the stability and reproducibility of the vapor sensor material remarkably improved. By the heat-treatment followed by the γ-ray radiation-treatment, a novel stable and reproducible sensor material was obtained, which allowed to identify and to quantify certain vapors in air accurately.

Temperature-switchable vapor sensor materials based on N-isopropylacrylamide and calcium chloride

Abstract A novel temperature-switchable vapor sensor was prepared by radiation-induced polymerization of N -isopropylacrylamide (NIPAAm) in an alcohol solution of calcium chloride (CaCl 2 ). The conductivity of the sensor material largely increased in water and ethanol vapors, but decreased against acetone, tetrahydrofuran, and chloroform vapors. The data showed a high level of reproducibility. In addition, the conductivity increased with the rise of temperature in ethanol vapor, showing a slight hysteresis, while against water vapor it exhibited a tendency to decrease with temperature accompanied by a large hysteresis. On the other hand, a densimeter to determine the water concentration in acetone solution was designed based on the opposite response of polyelectrolyte to two vapors, acetone and water, resulting in a linear responsiveness at low water concentration.

Photoisomerization of ammonium α,β-unsaturated carboxylates in the solid state: effect of the hydrogen-bond network on the reactivity

EZ-Photoisomerization has been attained for several kinds of salts of α,β-unsaturated carboxylic acids with amines. This photoreaction has been proven to be an effective method for preparing (Z)-isomers from ammonium (E)-α,β-unsaturated carboxylates. The isomerizability is strikingly altered upon changing the ammonium group, which implies that the crystal structure affected the reactivity to a considerable extent. However, the cavity in the crystal has been found to have less influence than expected on the isomerizability. A further detailed study concerning the crystal structures suggested that the characteristics of the hydrogen-bond network had a close correlation with the isomerizability. Moreover, both the bulkiness of the carboxylate and ammonium groups as well as their difference in molecular length are considered to be the most important factors influencing the isomerizability.

Degradation manner of polymer grafts chemically attached on thermally stable polymer films: swelling-induced detachment of hydrophilic grafts from hydrophobic polymer substrates in aqueous media

The degradation manner of graft-type polymer electrolyte membranes consisting of hydrophilic poly(styrenesulfonic acid) (PSSA) graft polymers (grafts) and thermally and mechanically stable hydrophobic polymer substrates such as crosslinked poly(tetrafluoroethylene) (cPTFE), poly(ethylene-co-tetrafluoroethylene) (ETFE), and poly(ether ether ketone) (PEEK) was examined in water at 85 and 95 °C. Severe weight loss was observed in PSSA-grafted cPTFE and ETFE films but not in a PSSA-grafted PEEK film. The decomposed extracts in water were characterized as PSSA during the whole course of degradation, clearly showing that the PSSA grafts detached from the fluorinated substrates without decomposition or scission of graft polymer chains. This is quite a new degradation manner for graft-type polymer electrolyte membranes. PSSA-grafted PEEK films showed severe weight loss in aqueous propanol solutions making PSSA grafts swell; clear correlation was observed between the degree of swelling in PSSA grafts and the film weight loss. The solubility parameters between grafts and the polymer substrates and small angle neutron scattering (SANS) data implied that the grafted films possessing a clear boundary at the interface resulted in significant weight loss. From the above observation, it should be concluded that hydrophilic PSSA grafts detach from hydrophobic polymer substrates due to swelling-induced stress at the interfacial boundary in the grafted films.

Polymerization of Diphenylbutadiyne by Gamma Rays Irradiation in the Molten State

Diphenylbutadiyne was irradiated with Gamma ray in the molten state (90°C), and its polymerization process was studied. The amorphous product has a number average molecular weight of around 1300. The yield reached around 20% with a dose of 3000 kGy, which is far greater than that in the case of irradiation in the solid state at room temperature. From the number of spins and molecular weights the product is thought to be mainly composed of cyclic oligomers. The third order nonlinear optical susceptibility of the products was found to be 3–6 × 10−10 esu determined by the Z-scan technique.

Preparation of Fuel Cell Membranes by Photografting in Vapor and Liquid Phases

UV radiation-induced photografting of styrene into poly(tetrafluoroethylene-co-ethylene) (ETFE) films for the preparation of fuel cell membranes was carried out. The proton conductivity in the thickness direction of membranes prepared by the vapor- and liquid-phase photografting can reach as high as 0.065 and 0.087 S/cm, respectively. The higher conductivity in the liquid-phase grafting is close to the homogeneity of graft chain distribution in the membrane.

Regioselectivity control of radiation-induced reaction: electron beam-induced Fries rearrangement of sulfonamide within a β-cyclodextrin inclusion complex

EB (electron beam) irradiation of sulfonamide within a beta-cyclodextrin (beta-CD) inclusion complex in the solid state induced the solvent-free Fries rearrangement, which proceeded at a shorter reaction time with reversed regioselectivity by inclusion into the beta-CD, compared with that of sulfonamide crystals; the beta-CD as a restricted nanospace had a large effect on the reactivity and regioselectivity of the solvent-free EB-Fries rearrangement.

Conductometric study of the radial track etch rate: Free shape analysis

Abstract A general formula for data analysis in conductometric experiments on latent track structure has been obtained without any pore shape assumption. An iterative equation, which was derived from pore geometry defined in a rest frame model, enables us to estimate the precise pore shape of the latent tracks during an etching. Polyethylene terephthalate (PET) films irradiated by Kr ions have been studied by this iteration technique. Radial etch rates reach convergence after a few iteration cycles and are less affected by the error of the breakthrough time. The iteration technique also reveals that a cylinder approximation, which is widely used for calculating a pore size, overestimates the transverse size of etched heavy ion tracks in the range less than 10 nm.

In-situ observation of dynamic water behavior in polymer electrolyte fuel cell by combined method of Small-Angle Neutron Scattering and Neutron Radiography

In-situ observation was conducted on an operating polymer electrolyte fuel cell with a combined method of small-angle neutron scattering (SANS) and neutron radiography (NR). The combined measurement system has been recently developed to visualize water in a wide length scale from nano- to millimeter and successfully detected a spatial distribution of the water generated in individual cell elements; NR macroscopically detected the water in a gas diffusion layer and a flow-field, whereas SANS microscopically did in a membrane electrode assembly. In particular SANS was found to be a strong tool to make a rather precise analysis on the water content inside of ion conducting channels of polymer electrolyte membrane.

Solution properties of polyamic acids and their amine salts

Solution properties such as viscosity, critical concentration, radius of gyration, and activation energy in aqueous solutions are described for [BPDA/PDA]polyamic acid (PAA) and their salts with various amines (PAS). Although PAA and their salts with Bu3N, Hex3N, Oct3N, and pyridine, were insoluble in H2O, only the salt with Et3N (PAS(Et3N)) was soluble in H2O. The different solubility of PAS suggests that higher base strength as well as shorter alkyl length of amines enhance water solubility of PAS. PAS(Et3N) showed critical concentrations at 18, 14, and 7.8 wt% in NMP, NMP/H2O (1/1), and H2O, respectively. The radius of gyration, which is calculated from the critical concentration, in H2O is 1.3 times larger than that in NMP; that is, the polymer chain expands in H2O rather than in NMP. PAS(Et3N) in H2O showed larger activation energy of viscosity than that in NMP. However, PAA and PAS(Et3N) showed similar activation energies in the NMP solution. Therefore, it is concluded that the amine salts of the polyamic acids are hydrated by several water molecules in H2O, resulting in the larger radius of gyration and lager activation energies.