Evaluation and fabrication of pore‐size‐tuned silica membranes with tetraethoxydimethyl disiloxane for gas separation

Organic/inorganic hybrid silica membranes were prepared from 1,1,3,3‐tetraethoxy‐1,3‐dimethyl disiloxane (TEDMDS) by the sol‐gel technique with firing at 300–550°C in N₂. TEDMDS‐derived silica membranes showed high H₂ permeance (0.3–1.1 × 10^?6 mol m^?2 s^?1 Pa^?1) with low H₂/N₂ (～10) and high H₂/SF₆ (～1200) perm‐selectivity, confirming successful tuning of micropore sizes larger than TEOS‐derived silica membranes. TEDMDS‐derived silica membranes prepared at 550°C in N₂ increased gas permeances as well as pore sizes after air exposure at 450°C. TEDMDS had an advantage in tuning pore size by the “template” and “spacer” techniques, due to the pyrolysis of methyl groups in air and Si? O? Si bonding, respectively. For pore size evaluation of microporous membranes, normalized Knudsen‐based permeance, which was proposed based on the gas translation model and verified with permeance of zeolite membranes, reveals that pore sizes of TEDMDS membranes were successfully tuned in the range of 0.6–1.0 nm. © 2011 American Institute of Chemical Engineers AIChE J, 2011     

Reverse osmosis performance of organosilica membranes and comparison with the pervaporation and gas permeation properties

Hybrid organosilica membranes were successfully prepared using bis(triethoxysilyl)ethane (BTESE) and applied to reverse osmosis (RO) desalination. The organosilica membrane calcined at 300^°C almost completely rejected salts and neutral solutes with low‐molecular‐weight. Increasing the operating pressure led to an increase in water flux and salt rejection, while the flux and rejection decreased as salt concentration increased. The water permeation mechanism differed from the viscous flow mechanism. Observed activation energies for permeation were larger for membranes with a smaller pore size, and were considerably larger than the activation energy for water viscosity. The organosilica membranes exhibited exceptional hydrothermal stability in temperature cycles up to 90^°C. The applicability of the generalized solution‐diffusion (SD) model to RO and pervaporation (PV) desalination processes were examined, and the quantitative differences in water permeance were accurately predicted by the application of generalized transport equations. © 2012 American Institute of Chemical Engineers AIChE J, 59: 1298–1307, 2013     

A method of single-phase PWM for an independent power supply in photovoltaic power generation systems

We propose a method of single-phase PWM for an independent power supply in photovoltaic power generation systems. This new PWM is derived by comparing levels of signal waves with one of carrier waves which have bipolar swing different from unipolar swing in the conventional PWM. In this PWM, we can use a battery with lower voltage in combination with the photovoltaic power generation; fundamental level of output voltage is raised by about 11%, though poor in quality of waveforms. © 1998 Scripta Technica. Electr Eng Jpn, 122(4): 55–62, 1998     

Copper(I) catalyzed asymmetric oxidative cross-coupling copolymerization leading to alternating copolymers

The asymmetric oxidative coupling copolymerization of 6,6′-dihydroxy-2,2′-binaphthalene and dihexyl 6,6′-dihydroxy-2,2′-binaphthalene-7,7′-dicarboxylate with the copper(I)-diamine catalysts under an O₂ atmosphere was carried out. The copolymerization using the CuCl-(S)-(−)-2,2′-isopropylidenebis(4-phenyl-2-oxazoline) catalyst [(S)Phbox], afforded a polymer with the high cross-coupling selectivity of 93%, that is, a copolymer with a mainly alternating structure, in 80% yield. The number-average molecular weight of the methanol-ethylacetate (1/3 v/v)-insoluble part of the copolymer was 1.1×10⁴. To estimate the enantioselectivity with respect to the cross-coupling linkage in the obtained copolymer, the model asymmetric oxidative cross-coupling reaction with CuCl-(S)Phbox was also examined, and the products showed a 96% cross-coupling selectivity and enantioselectivity of 43% ee (S).     

Transient shift of local oxygen potential in nonstoichiometric oxides upon application of mechanical stress

Effect of mechanical stress on defect equilibrium was studied with an oxygen nonstoichiometric compound, La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ . In general, formation of oxygen vacancy in an oxide causes lattice expansion, which leads to stabilization of oxygen vacancy in the material under a tensile stress, and vice versa. Oxygen vacancy concentration is thus expected to increase under a tensile stress and decrease under a compressive stress. However, the change in defect concentration would not proceed spontaneously so that the material just after the application of stress would stay out of equilibrium. On this assumption, attempts were made to detect the shift of oxygen potential under stress using a potentiometric method. A ball-shaped yttria stabilized zirconia (YSZ) of 9.5 mm in diameter was utilized as an oxygen potential sensor as well as a pushing rod which was pressed onto the sample surface. In the measurements at 873 K to 1073 K, a clear shift of emf to the negative direction was observed depending on the magnitude of load and loading speed. It was followed by a relaxation to the initial value under the stress. On unloading operation, the shift of emf to the positive direction was observed. Those behaviors were well explained by the assumption that the oxygen vacancy concentration varies under mechanical stress.     

Structures and dynamics of microparticles in suspension studied using ultrasound scattering techniques

Ultrasonic waves are widely employed in medical diagnosis and non‐destructive testing to observe the condition of fetuses and to study non‐transparent materials, respectively. Although ultrasonic waves are mostly applied to relatively large‐scale structures, megahertz ultrasound has been utilized to investigate the microstructure of particulate matter and the local dynamics of soft matter. More recently, due to the development of high‐speed recording technology with large memory storage and sophisticated techniques employing scattered amplitude and phase, analyses of the dynamics as well as the structures of highly turbid suspensions are possible for a wide range of concentrations and particle sizes (several tens of nanometers to several tens of micrometers) using new routes. The technology could simultaneously allow the investigation of complex dynamics involving the Brownian motion of nanoparticles and sedimentation due to the formation of large aggregates. The advantages of using ultrasound are not only the applicability to optically turbid systems but also the wave characteristics related to mechanical (viscoelastic) information, allowing one to evaluate the elastic moduli of particular components, e.g. the elastic shell of a microcapsule immersed in liquid without dilution or drying of the sample. In this paper, the recent developments of novel ultrasound techniques for soft matter characterization are reviewed. © 2016 Society of Chemical Industry     

Molecular dynamics simulation for investigating and assessing reaction conditions between carboxylated polyethersulfone and polyethyleneimine

Recently, nano-filtration membranes are made by the reaction between a reactive functional group on the surface of a tight ultrafiltration membrane and a charged branched polymer. This reaction makes the selective layer of the nanofiltration membrane, which plays an essential role in membrane performance. A molecular dynamics simulation with a reactive force field was used to investigate the reaction of carboxylated polyethersulfone as the functional group of the ultrafiltration membrane with polyethyleneimine. Experimental elucidation of the reaction between the PEI amine and carboxyl groups is challenging, and an MD simulation was thus employed. Furthermore, the simulation results show that the PEI and carboxylated polyethersulfone polymers react with each other in a temperature-dependent manner. While no reaction occurs at 298 K, carboxylated polyethersulfone and PEI begin to react when the temperature is increased from 298 to 323 K. Furthermore, a reversible reaction was observed with a subsequent increase in temperature to 353 K.