Temperature dependence of ion and water transport in perfluorinated ionomer membranes for fuel cells

To clarify the mechanisms of transport of ions and water molecules in perfluorosulfonated ionomer membranes for fuel cells, the temperature dependence of their transport behaviors was investigated in detail. Two types of Flemion membranes having different equivalent weight values (EW) were utilized along with Nafion 117 as the perfluorinated ionomer membranes, and H-, Li-, and Na-form samples were prepared for each membrane by immersion in 0.03 M HCl, LiCl, and NaCl aqueous solutions, respectively. The ionic conductivity, water self-diffusion coefficient (D(H)(2)(O)), and DSC were measured in the fully hydrated state as a function of temperature. The ionic conductivity of the membranes was reflected by the cation transport through the intermediary of water. Clearly, H(+) transports by the Grotthuss (hopping) mechanism, and Li(+) and Na(+) transport by the vehicle mechanism. The differences of the ion transport mechanisms were observed in the activation energies through the Arrhenius plots. The D(H)(2)(O) in the membranes exhibited a tendency similar to the ionic conductivity for the cation species and the EW value. However, no remarkable difference of D(H)(2)(O) between H- and the other cation-form membranes was observed as compared with the ionic conductivity. It indicates that water in each membrane diffuses almost in a similar way; however, H(+) transports by the Grotthuss mechanism so that conductivity of H(+) is much higher than that of the other cations. Moreover, the D(H)(2)(O) and DSC curves showed that a part of water in the membranes freezes around -20 degrees C, but the nonfreezing water remains and diffuses below that temperature. This fact suggests that completely free water (bulk water) does not exist in the membranes, and water weakly interacting with the cation species and the sulfonic acid groups in secondary and higher hydration shells freezes around -20 degrees C, while strongly binding water in primary hydration shells does not freeze. The ratio of freezing and nonfreezing water was estimated from the DSC curves. The D(H)(2)(O) in the membranes was found to be influenced by the ratio of freezing and nonfreezing water. DFT calculation of the interaction (solvation) energy between the cation species and water molecules suggested that the water content and the ratio of freezing and nonfreezing water depend strongly on the cation species penetrated into the membrane.     

Geometrical Evolution and Formation of the Photoproduct in the Cycloreversion Reaction of a Diarylethene Derivative Probed by Vibrational Spectroscopy

The geometrical evolution of the reactant and formation of the photoproduct in the cycloreversion reaction of a diarylethene derivative were probed using time-resolved absorption spectroscopies in the visible to near-infrared and mid-infrared regions. The time-domain vibrational data in the visible region show that the initially formed Franck-Condon state is geometrically relaxed into the minimum in the excited state potential energy surface, concomitantly with the low-frequency coherent vibrations. Theoretical calculations indicate that the nuclear displacement in this coherent vibration is nearly parallel to that in the geometrical relaxation. Time-resolved mid-infrared spectroscopy directly detected the formation of the open-ring isomer with the same time constant as the decrease of the closed-ring isomer in the excited state minimum. This observation reveals that no detectable intermediate, in which the population is accumulated, is present between the excited closed-ring isomer and the open-ring isomer in the ground state.     

Study of adsorption of methylene blue and new methylene blue in liquid-solid interface by slab optical waveguide spectroscopy

A slab optical waveguide (SOWG) has been used for study of adsorption of both methylene blue (MB) and new methylene blue (NMB) in liquid–solid interface. Adsorption characteristics of MB and NMB on both bare SOWG and silanized SOWG by octadecyltrichlorosilane (ODS) were compared. Effect of pH on adsorption on MB and NMB was investigated. Binding rate constant analysis showed that both MB and NMB on bare SOWG demonstrates larger association constants than those on ODS-SOWG. Interactions of MB and NMB on bare SOWG and ODS-SOWG were analyzed by molecular mechanics calculation method. The binding energy change was in the following order: E_NMB–bare > E_MB–bare > E_NMB–ODS > E_MB–ODS.     

Simultaneous determination of methylene blue and new methylene blue by slab optical waveguide spectroscopy and artificial neural networks

A slab optical waveguide (SOWG) has been used for study of adsorption of both methylene blue (MB) and new methylene blue (NMB) in liquid-solid interface. Adsorption characteristics of MB and NMB on both bare SOWG and silanized SOWG by octadecyltrichlorosilane (ODS) were compared. The simultaneous determinations of both MB and NMB were explored by flow injection SOWG spectrophotometric analysis and artificial neural networks (ANNs) for the first time. Concentrations of MB and NMB were estimated simultaneously with the ANNs. Results obtained with SOWG were compared with those got by conventional UV-visible spectrophotometry.     

Direct Observation of Ordered High‐Spin–Low‐Spin Intermediate States of an Iron(III) Three‐Step Spin‐Crossover Complex

A neutral mononuclear Fe^III complex [Fe^III(H‐5‐Br‐thsa‐Me)(5‐Br‐thsa‐Me)]?H₂O ( 1 ; H₂‐5‐Br‐thsa‐Me=5‐bromosalicylaldehyde methylthiosemicarbazone) was prepared that exhibited a three‐step spin‐crossover (SCO) with symmetry breaking and a 14 K hysteresis loop owing to strong cooperativity. Two ordered intermediate states of 1 were observed, 4HS–2LS and 2HS–4LS, which exhibited reentrant phase‐transition behavior. This study provides a new platform for examining multistability in SCO complexes.     

Solid-phase synthesis of 2,3-diphenylpropionic acid library as VLA-4 antagonists

2,3-Diphenylpropionic acid library for VLA-4 antagonist was synthesized on solid-phase. Comparison of the two synthetic routes via an orthogonal generation of two aromatic amino functional groups are discussed. From this work, several compounds were identified as potent VLA-4 antagonists.     

Crystal structure of ethene-/α-olefin copolymers with various long comonomers (C8–C26)

Ethene-/α-olefin copolymers having a wide range of comonomers between 8 and 26 carbon atoms in length were characterized by wide angle X-ray diffraction (WAXD). It was found that the crystallinities for the shorter comonomers (C₈, C₁₂) matched fairly well with the crystallinities from DSC and volumetric measurements, while for the longer comonomers (C₁₈, C₂₆) distinct differences between the three methods were found. This was explained by the presence of an additional crystalline phase of the side chains slightly deforming the amorphous peak.     

Single-component organic semiconductors based on novel radicals that exhibit electrochemical amphotericity: preparation, crystal structures, and solid-state properties of N,N'-dicyanopyrazinonaphthoquinodiiminides substituted with an N-alkylpyridinium unit.

N,N'-Dicyanonaphthoquinodiimines fused with a pyrazine ring 1 were prepared from the corresponding quinones 4. The new acceptors 1 have a planar pi-system and undergo reversible two-stage 1e-reduction. Quaternization of the pyridyl substituent in 1d-f gave pyridinium derivatives 2d+, 2e+, and R-3+, respectively, which are stronger acceptors that undergo three-stage 1e-reduction. Upon electrochemical reduction of these cations, novel radicals 2d., 2e., and R-3. were generated and isolated as stable solids. The molecular geometries determined by X-ray analysis indicated that these radicals adopt a zwitterionic structure, in which the unpaired electron is located on the quinodiimine unit but not on the pyridyl group. These novel radicals undergo facile and reversible 1e-oxidation as well as two-stage 1e-reduction. The observed amphotericity endows the radicals with electrical conductivities (10(-5) to 10(-9) S cm-1), and these thus represent a new motif for single-component organic semiconductors.