CO2-permselective membranes of crosslinked poly(vinyl ether)s bearing oxyethylene chains

Cationic copolymerizations of vinyl ether monomers having a triethylene glycol segment [2-(2-(2-methoxyethoxy)ethoxy)ethyl vinyl ether (TEGMVE)] with vinyl ether monomer having a methacrylate unit [2-(2-vinyloxyethoxy)ethyl methacrylate: VEEM] were performed to obtain crosslinkable copolymers [poly(TEGMVE-VEEM)] with different composition rates. Methacrylate groups in poly(TEGMVE-VEEM)s partially reacted to give crosslinked polymer membranes. The free-standing membranes of poly(TEGMVE-VEEM)s obtained at monomer feed ratios of 6:1, 10:1, and 14:1 were too brittle, while their composite membranes with PTFE sheet were tough enough to measure gas permeability. All the membranes of poly(TEGMVE-VEEM) showed high CO₂/N₂ selectivity (PCO₂/PN₂$P_{{\text{CO}}_2}/P_{{\text{N}}_2}$ = 35–54) because of their high CO₂ solubility selectivity (SCO₂$S_{{\text{CO}}_2}$/SN₂$S_{{\text{N}}_2}$ = 38–61). The gas permeability increased as the composition ratio of VEEM decreased, and the composite membrane of poly(TEGMVE-VEEM)(14:1) showed the highest CO₂ permeability (PCO₂$P_{{\text{CO}}_2}$ = 410 barrers) among the present polymer membranes.     

Relationship between the local dynamics and gas permeability of polyacetylenes containing polymethylated indan/tetrahydronaphtalene moieties

Local dynamics of polyacetylenes having polymethylated indan/tetrahydronaphthalene moieties have been studied using quasielastic neutron scattering, and the results obtained have been discussed together with former results with various poly(diphenylacetylene) derivatives. Clear quasielastic scattering was observed for the present polymers although they were in the glassy state, and the observed dynamic scattering laws were well fitted to a model function assuming the sum of narrow and broad Lorentzians. Both the relaxation rates and fractions from the narrow component exhibited a positive correlation with oxygen permeability coefficients (PO₂)$\left(P_{{\text{O}}_2}\right)$, while those from the broad component hardly related to PO₂$P_{{\text{O}}_2}$. Furthermore, the local flux, which is defined as the product of fraction and relaxation rate of the narrow component, is also found to be proportional to PO₂$P_{{\text{O}}_2}$. These findings imply that only the narrow component contributed to the gas permeability. Thus, it has been clarified that the local dynamics with a time scale of several tens of picoseconds plays a role of key importance for the gas permeability of substituted polyacetylenes in the glassy state.     

Dielectric properties of Cf–Si3N4 sandwich composites prepared by gelcasting

C_f–Si₃N₄ sandwich composites were prepared by gelcasting using α-Si₃N₄ powder, SiC-coated carbon fibers and sintering additives as starting materials. The microstructure and composition, dielectric properties of C_f–Si₃N₄ sandwich composites were investigated. SEM and EDS analysis results reveal that the SiC interphase could effectively overcome incompatibility between carbon fiber and silicon nitride matrix under the condition of pressure-less sintering at 1700 °C. The investigation of microwave absorbing property reveals that, compared with the Si₃N₄ ceramics, both the real (ε?$\epsilon ?$) and imaginary (ε??$\epsilon ??$) permittivity of C_f–Si₃N₄ sandwich composites show strong frequency dispersion characteristics at X-band. Microwave absorption ability of the C_f–Si₃N₄ sandwich composites are significantly enhanced compared with pure Si₃N₄ ceramic, and the reflection loss gradually decreases from −3.5 dB to −14.4 dB with the increase of frequency, while the pure Si₃N₄ ceramic keeps at −0.1 dB. Particularly, the relationship between permittivity of C_f–Si₃N₄ sandwich composites and frequency at X-band has been established through an equivalent RC circuit model. Results showed that both ε?$\epsilon ?$ and ωε??$\omega \epsilon ??$ are inversely proportional to the frequency square ω²${\omega }^2$, and the predicted results agree quite well with the measured data.     

Facile synthesis of five 2D surface modifiers by highly selective photocyclic aromatization and efficient enhancement of oxygen permselectivities of three polymer membranes by surface modification using a small amount of the 2D surface modifiers

A facile synthesis of novel five 2D (planar) surface modifiers having a triphenylbenzene derivatives as a 2D structure has been achieved by the highly selective photocyclic aromatization reaction. Efficient enhancement of oxygen permselectivities through the three polymer membranes has been achieved by adding a small amount (<5.0 wt%) of the 2D surface modifiers. Among the five 2D surface modifiers, a modifier compound having oligoethylene oxide groups showed the best performance for the enhancement. These improvements were thought to be caused mainly by improvement of the solution selectivity on the membrane surface where the 2D surface modifiers were accumulated. In some of the surface-modified blend membranes, their plots in the PO₂$P_{{\text{O}}_2}$-α graph were over or close to the upper boundary line by Robeson in 1991. Since all the membranes containing the 2D surface modifiers showed better permselectivities than the corresponding substrate membranes, it is very promising for the future.     

Microwave dielectric properties of neodymium tin oxide

The microwave dielectric properties of Nd₂Sn₂O₇ ceramics were investigated with a view to their application in mobile communication. Nd₂Sn₂O₇ ceramics were prepared by the conventional solid-state method with various sintering durations. A maximum density of 7.11 g/cm³, a dielectric constant (_εr${\epsilon }_r$) of 17.02, a quality factor (Qf) of 33,100 GHz, and a temperature coefficient of resonant frequency (_τf${\tau }_f$) of −55 ppm/°C were obtained when Nd₂Sn₂O₇ ceramics were sintered at 1550 °C for 9 h.     

Flow separation from a spherical particle in supercritical water

Flow separation from a spherical particle in supercritical water (SCW) is the basic flow structure in supercritical water fluidized bed (SCWFB). In order to study flow separation from a spherical particle in SCW in detail, a numerical model fully accounting for variations in thermo-physical properties has been developed in the pseudo-critical zone. Flow separation parameters (separation angle, length of wake vortex, width of wake vortex, and drag coefficient) for forced convection, assisting convection, and opposing convection have been obtained at intermediate Reynolds numbers. Results show that variable viscosity has a remarkable effect on flow separation, and the decreasing viscosity results in higher velocity gradient around the sphere particle surface and a larger wake vortex on the rear particle surface. A simple expression of Cd/Cdc=(μw/μf)^0.15$\text{Cd}/{\text{Cd}}_{\text{c}}={({\mu }_{\text{w}}/{\mu }_{\text{f}})}^{0.15}$ is achieved to predicate the drag coefficient of the SCW flow with μw/μf${\mu }_{\text{w}}/{\mu }_{\text{f}}$ between 0.7 and 1.0. Free convection inhibits the flow separation of the assisting convection, but enhances the flow separation of the opposing convection. Three flow separation zones (the rear-end separation zone, the transition zone, and the reversed flow zone) are observed for the opposing convection.     

Growth and optical properties of cerium dioxide nanocrystallites prepared by coprecipitation routes

Nanosized cerium dioxide (CeO₂) powders have been synthesized using coprecipitation methods and cerium nitrate hexahydrate (Ce(NO₃)₃·6H₂O) as the starting material. The growth and optical properties of nanosized CeO₂ powders were investigated using X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED), nano-beam electron diffraction (NBED), high resolution TEM (HRTEM), and ultraviolet–visible (UV–vis) absorption spectrophotometry. The XRD result shows that the dried CeO₂ precursor powders (both before and after calcination at various temperatures and times) contained a single crystalline phase of CeO₂. In the dried precursor powders, the crystallites of CeO₂ measured 10.4 nm and 66.8 nm before and after calcination at 1273 K for 240 min, respectively. The indirect band gap energy (_Ei$E_i$) of CeO₂ decreased from 3.03 eV to 2.68 eV as the crystallite size increased from 10.4 nm to 66.8 nm, whereas the direct band gap energy (_Ed$E_d$) of CeO₂ also decreased from 3.79 eV to 3.38 eV.     

Study of the rate of liquid–solid mass transfer controlled processes in helical tubes under turbulent flow conditions

The liquid–solid mass transfer behaviour of helical tubes was studied by the diffusion controlled dissolution of copper tubes in acidified dichromate. Variables studied were solution velocity, tube diameter, coil diameter and physical properties of the solution. The effect of drag reducing polymers on the rate of mass transfer in the helical tubes was also studied. The blank solution mass transfer data were correlated for the conditions 850 < Sc < 1322; 6000 < Re < 23,400 and 5 < d_c/d < 25 by the equation.

Sh=0.107Sc0.33Re0.68$Sh=0.107S{c}^{0.33}R{e}^{0.68}$

Electron-Capture Cross Sections of Ground-State O2+ Recoil Ions in Slow Collisions with H2 and O2

We report the measured total charge-transfer (electron-capture) cross sections for the ground state O2+ (X2Πg) ions with H₂ and O₂ molecular gases in the collision energy range between 0.50 and 2 keV. The time-of-flight technique has been used to measure the fast neutral products from O2+ charge transfer reactions. The analyzed process has cross sections that continue to increase slowly, as a function of incident energy. Measured cross sections for O2++H2, O₂ systems are compared with previously available experimental and theoretical results in the literature.