Molecular dynamics studies on the structures of polymer electrolyte membranes and diffusion mechanism of protons and small molecules

We performed a series of molecular dynamics (MD) simulations on Nafion^® membranes containing various quantities of H₂O and CH₃OH. The simulations afforded diverse nanoscale phase-separated structures, such as clusters, channels, and cluster–channels. The calculated cluster–channel structure qualitatively agrees with the experimental results of X-ray diffraction studies. We also investigated the diffusion mechanisms for H₂O, protons, CH₃OH, H₂, and O₂ in these membranes. To reproduce the hopping transfer of protons, we employed a semi-classical MD approach using the empirical valence bond method. The estimated diffusion coefficients of H₂O and proton in the membranes significantly depended on the H₂O content, and these values showed qualitatively good agreement with the experimental results. The diffusion coefficient of proton in H₂O-rich membranes was much larger than that of H₂O, and the proton mainly formed H₅O₂⁺ complex. Furthermore, the simulation results indicate that the majority of CH₃OH permeates through the H₂O clusters, and the majority of H₂ and O₂ permeates through the hydrophobic region of the membrane.     

Excess Adsorption of Helium in Extremely Narrow Slit Pores

Wave functions of quantum helium in narrow slit pores are strongly restricted; as such, quantum helium condensed in narrow slit pores displays different behaviors from that in bulk. Herein, we report the densities of helium adsorbed on carbon surfaces and in carbon slit pores with average pore widths of 0.7, 0.9, and 1.1 nm at 2–5 K. The density of adsorbed quantum helium in the 0.7-nm slit pores was significantly higher than those in the larger slit pores and bulk. The average layer density of helium in the 0.7-nm pores was also significantly higher than those in the larger slit pores, suggesting solid-like structure formation even under helium vapor condition. The highly dense state of helium in narrow slit pores is due to strong attractive potential effects in such slit pores.     

Relationship between Rice Flour Particle Sizes and Expansion Ratio of Pure Rice Bread

We examined a method to produce bread from crystalline rice flour without using thickening agents such as gluten, polysaccharide thickening, and amorphous rice flour. Rice grains were pulverized by a jet mill to produce flour. Samples of rice flours of various particle size distributions were prepared by using a size shifter. The degree of starch damage and the dynamic viscoelasticity of rice batter were measured in this work. We also baked bread of the flour of each size distribution to study processability for making bread. The batter made by the pulverized flour of rice particle size ranging from 75 to 106 μm had the highest expansion ratio and a good processability for baking breads compared to other particle size batters. The rice bread with high expansion ratio was produced by controlling particle size of crystalline rice flour without using thickening agents.     

Electrochemical oxidation of cholesterol in acetonitrile leads to the formation of cholesta-4,6-dien-3-one

Cholesterol was shown to be oxidized at the glassy carbon electrode in an acetonitrile–2-propanol mixture and this oxidation reaction was applied to the determination of serum total cholesterol by high-performance liquid chromatography with electrochemical detection (K. Hojo, H. Hakamata, A. Ito, A. Kotani, C. Furukawa, Y.Y. Hosokawa, F. Kusu, J. Chromatogr. A 1166 (2007) 135–141). To gain insight into the detection mechanisms of cholesterol, an electrolytic product of cholesterol was collected and characterized by infrared spectroscopy, one- and two-dimensional nuclear magnetic resonance, and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. The three techniques, together with comparisons of literature spectral data, confirmed the formation of cholesta-4,6-dien-3-one. The conversion of cholesterol to cholesta-4,6-dien-3-one, a four-electron, four-proton electrochemical process, has been proposed as an electrochemical oxidation mechanism of cholesterol in acetonitrile.     

Investigation of ionic polymer cathode binders for microbial fuel cells

Microbial fuel cell (MFC) air cathodes examined here were made using poly(phenylsulfone) (Radel^®) binders sulfonated to various ion exchange capacities (IECs). We examined the effect of increasing the IEC of poly(phenylsulfone) Radel binders from 0 to 2.54 meq/g on cathode performance using linear sweep voltammetry (LSV), impedance, and single chamber air-cathode MFC tests. Unsulfonated Radel, which is a non-ionic, hydrophobic polymer, showed the highest current in LSV tests and the lowest charge transfer resistance. Increasing the binder IEC resulted in a decreased current response in LSV tests and an increased charge transfer resistance from 8 to 23 Ω. It is proposed that the presence of sulfonate groups in the cathode binder impeded the oxygen reduction activity of the cathodes by adsorption of the sulfonate to catalytic sites and by impeding proton diffusion to the catalyst surface. The unsulfonated Radel binder produced the most stable performance, and eventually the highest power density, in MFCs operated over 20 cycles (55 days). These results suggest that the use of a non-ionic binder is advantageous in an MFC cathode to facilitate charge transfer and stable performance in the neutral pH conditions found in MFCs.     

Investigation on sensitivity of a polymer/carbon nanotube composite strain sensor

Extensive numerical simulation and experimental measurements have been conducted to understand the effects of processing parameters and material properties on sensor sensitivity in polymer/carbon nanotube (CNT) composite sensors. The numerical simulation was based on an improved three-dimensional statistical resistor network model incorporating the tunneling effect between the neighbouring nanotubes, and a fiber reorientation model. The behaviors of a sensor subjected to both tensile and compressive strains were investigated. Both numerical and experimental results indicate that a higher tunneling resistance or higher ratio of the tunneling resistance to the total resistance of the sensor leads to a higher sensor sensitivity. Processing conditions and material properties, such as weight fraction, diameter and conductivity of CNTs, curing temperature, mixing rate and barrier height of polymer matrix all play a role in determining the sensor sensitivity.     

A parallel iterative partitioned coupling analysis system for large-scale acoustic fluid–structure interactions

In many engineering fields, dynamic response in fluid–structure interaction (FSI) is important, and some of the FSI phenomena are treated as acoustic FSI (AFSI) problems. Dynamic interactions between fluids and structures may change dynamic characteristics of the structure and its response to external excitation parameters such as seismic loading. This paper describes a parallel coupling analysis system for large-scale AFSI problems using iterative partitioned coupling techniques. We employ an open source parallel finite element analysis system called ADVENTURE, which adopts an efficient preconditioned iterative linear algebraic solver. In addition, we have recently developed a parallel coupling tool called ADVENTURE_Coupler to efficiently handle interface variables in various parallel computing environments. We also employ the Broyden method for updating interface variables to attain robust and fast convergence of fixed-point iterations. This paper describes key features of the coupling analysis system developed, and we perform tests to validate its performance for several AFSI problems. The system runs efficiently in a parallel environment, and it is capable of analyzing three-dimensional-complex-shaped structures with more than 20 million degrees-of-freedom (DOFs). Its numerical results also show good agreement with experimental results.     

Development of advanced expansion due to compression (A-EDC) test method for safety evaluation of degraded nuclear fuel cladding materials

Expansion due to compression (EDC) test has been applied to evaluate the performance of nuclear fuel claddings where pellet-cladding mechanical interaction (PCMI) is introduced by swelling of fuel pellets and is triggered by the larger hoop deformation of the pellets, especially during accidental transients. The purpose of this study is to modify the EDC test to describe PCMI, specimen volume reduction and others. Ring-shaped specimens were cut from Zry-4 cladding tubes. Cylindrical metal pellets with 8 mm in diameter and 15 mm in maximum height were used as inner pellets. Expansion of the specimens due to the inner pellet compression was performed at room temperature. The experimental data were further analyzed by finite element method. Through the survey in the variation of the specimen and core, specimen size and inner pellet geometry were optimized. Excellent reproducibility with less error was confirmed. The uniaxial tension condition in the hoop direction up to the specimen failure was confirmed. Hoop stress–hoop strain curves were successfully derived.     

Characterization of microorganisms at different landfill depths using carbon-utilization patterns and 16S rRNA gene based T-RFLP

A borehole core from 20 m depth of a Japanese landfill was characterized chemically and microbially. The borehole core sample was typically divided into 5 waste layers; 2.4–4.0 m, 5.7–8.5 m, 9.25–9.6 m, 9.77–14.9 m, and 15.9–17.86 m depths. The waste layers' ages spanned about 14 years between the bottom and top. Archaeal 16S rRNA gene and eubacterial 16S rRNA gene in the waste samples at their respective levels were 9.8 × 10⁵–7.2 × 10⁷ and 1.2 × 10⁷–7.2 × 10⁹ copy/g-wet. Similar to populations of viable and culturable bacteria, those populations were high at 7.0 m and 17.5 m depth, but low at 3.0 m depth. The microorganisms' phenotypes and genotypes were evaluated, respectively, using carbon-utilization tests and by eubacterial 16S rRNA gene based T-RFLP. Low dominance of the VFA-utilizing bacteria in samples and low concentrations of VFAs in all waste layers suggest that the organic decomposition in this landfill site remained. Gamma-proteobacteria dominated the microbial community at 17.5 m depth. Clostridia were detected at 7.0, 11.5, and 17.5 m depths, suggesting strict anaerobic conditions in these deep layers. The Shannon–Weaver diversity index showed lower values at 3.0 m and 11.5 m depth with a T-RF pattern. The diversity index calculated from the carbon-utilization pattern increased slightly with depth at the landfill site. The landfill-site waste layers are expected to be mutually isolated and to form unique microbial communities depending on the buried wastes' composition, temperature, moisture content, and pressure inside the landfill.