Correlation between Performances of Hollow Fibers and Flat Membranes for Gas Separation

This work presents an attempt at correlating the available permeability/selectivity literature data for hollow fibers and flat membranes. Therefore, this paper gathers the information pertaining to membrane materials for which membrane properties of flat membranes and hollow fibers have both been reported. An overview of the relations between selectivity and permeance of hollow fiber membranes for various gas pairs (O₂/N₂, CO₂/CH₄, CO₂/N₂, H₂/N₂, H₂/CO₂, H₂/CH₄ and He/N₂) is presented first. The upper bound lines are the ones proposed by Robeson, which were calculated by assuming a one-micron-thick skin layer as proposed by Robeson in 2008. From the results obtained, a relation between the selectivity ratio in both kinds of membranes (α_H/α_f) and skin layer thickness (l) calculated from flat membranes and hollow fibers gas permeation data for these pairs of gases is also presented. The skin layer thicknesses measured using seven different experimental techniques for six commercial membranes are compared. The influences of spinning parameters on the morphology and performance of hollow fiber membrane gas separation are discussed. Finally, an analysis is made of the reasons why the dense skin layer thicknesses of a hollow fiber calculated using permeance and permeability data vary for different gases and also differ from direct experimental measurements.     

Ferric metal-organic framework for microwave absorption

In this study, we have shown for the first time that ferric metal-organic framework (Fe-MOF) has the ability to attenuate gigahertz-range electromagnetic radiation through means of a novel interference mechanism. A large reflection loss value of ?54.2 dB can be obtained, equivalent to over 99.999% absorption efficiency. The microwave absorption performance is largely dependent on the dielectric permittivity and magnetic permeability properties. The electrical loss ratio tgδ_ε increases with the frequency from 0.13 at 1.0 GHz to 0.69 at 18.0 GHz, while the magnetic loss ratio tgδ_μ is only between 0.05 and 0.14. The conductivity σ increases with the frequency from 0.08 S/m at 1.0 GHz to 5.24 S/m at 18.0 GHz, while the skin-depth δ decreases with the frequency. The thickness (d) of the absorber is inversely proportional to the reflection loss peak value (RL_peak), the reflection loss peak frequency (f_peak), and the critical reflection loss peak width (Δf₁₀). The non-zero magnetic susceptibility (χ) accelerates the shift of f_peak to lower values as d grows bigger; however, it improves the RL_peak value and larger microwave absorption efficiency and reduces the quick narrowing of the critical frequency range. The microwave performance of Fe-MOF is likely related to its microwave conductivity, which may originate from the polar rotations in the interface or defects. A new mechanism is proposed for the large reflection loss based on the interference of the reflected microwave from the front and back surface of the microwave absorber, especially when the thickness matches with the odd integer values of the wavelength.     

Structure and permeability of gels

The textures of silica gels made by two-step acid/base and acid/acid catalysis of TEOS have been examined by thermoporometry (TPM) and NMR, and their permeabilities (D) have been measured by a thermal expansion technique. Using the pore size distribution given by TPM, which includes a large proportion of macropores (30 nm), calculated values of D are seriously overestimated. We conclude that, consistent with a theoretical prediction, compliant materials such as gels undergo contraction during freezing in the calorimeter, so that most of the macropore volume reported by TPM is actually extracted from mesopores. The mesopore radius reported by TPM is underestimated by only 20%, even if 50% of the pore liquid is drained during crystallization, assuming that the change in pore radius is related to the cube root of the volume change. NMR does not distinguish macropores, because of diffusional averaging, but provides an apparent distribution that permits an accurate estimate of the permeability.     

Detailed study of ultra-soft magnetic properties of Fe74Cu0.8Nb2.7Si15.5B7

The magnetic properties of nanocrystalline Fe₇₄Cu_0.8Nb_2.7Si_15.5B₇ alloy, which were rapidly solidified and then annealed at various temperatures between 475 and 650°C for different holding time, have been studied. Grain size, silicon content and the lattice parameter of α-Fe(Si) nanograins at the annealing temperatures were determined. Curie temperature of the amorphous phase was determined from the temperature dependence of permeability. For higher annealing temperatures and times, some Si diffused out of the α-Fe(Si) phase and formed an ordered DO₃ phase of Fe₃Si. This changed the overall magnetostriction and average anisotropy of the matrix, which deteriorated the magnetic softness of the material at higher annealing temperatures. Ultra-soft magnetic properties were achieved by averaging the random anisotropy via exchange interaction. Hysteresis loops for samples in as-cast and annealed conditions have also been studied.     

Nanoformulation Development to Improve the Biopharmaceutical Properties of Fisetin Using Design of Experiment Approach

This study aimed to design an effective nanoparticle-based carrier for the oral delivery of fisetin (FST) with improved biopharmaceutical properties. FST-loaded nanoparticles were prepared with polyvinyl alcohol (PVA) and poly(lactic-co-glycolic acid) (PLGA) by the interfacial deposition method. A central composite design of two independent variables, the concentration of PVA and the amount of PLGA, was applied for the optimization of the preparative parameter. The responses, including average particle size, polydispersity index, encapsulation efficiency, and zeta potential, were assessed. The optimized formulation possessed a mean particle size of 187.9 nm, the polydispersity index of 0.121, encapsulation efficiency of 79.3%, and zeta potential of −29.2 mV. The morphological observation demonstrated a globular shape for particles. Differential scanning calorimetry and powder X-ray diffraction studies confirmed that the encapsulated FST was presented as the amorphous state. The dissolution test indicated a 3.06-fold increase for the accumulating concentrations, and the everted gut sac test showed a 4.9-fold gain for permeability at the duodenum region. In conclusion, the optimized FST-loaded nanoparticle formulation in this work can be developed as an efficient oral delivery system of FST to improve its biopharmaceutic properties.     

直接甲醇燃料电池用阻醇质子导电聚乙烯醇-聚苯乙烯磺酸共混膜

制备了聚乙烯醇 (PVA)与聚苯乙烯磺酸 (PSSA)的共混膜 ,并研究了膜的组成、热处理温度、甲醇水溶液浓度等对膜电导率和甲醇透过率的影响。与目前普遍使用的NafionTM膜相比 ,这种由阻醇材料PVA与离子交换材料PSSA共混后形成的聚合物膜既能提高阻醇性能 ,又具有一定的电导率。一种以聚苯乙烯磺酸含量为 17%的膜 ,其电导率可达 3× 10 -3 S·cm-1,但甲醇透过率P仅为 2× 10 -8cm2 ·s-1。如果以σ/P为综合指标 ,则此膜的综合性能比NafionTM膜高约 4 0倍     

Synthesis of sulfonated poly(imidoaryl ether sulfone) membranes for polymer electrolyte membrane fuel cells

New sulfonated poly(imidoaryl ether sulfone) copolymers derived from sulfonated 4,4′‐dichlorodiphenyl sulfone, 4,4′‐dichlorodiphenyl sulfone, and imidoaryl biphenol were evaluated as polymer electrolyte membranes for direct methanol fuel cells. The sulfonated membranes were characterized with Fourier transform infrared spectroscopy, thermogravimetric analysis, and proton nuclear magnetic resonance spectra. The state of water in the membranes was measured with differential scanning calorimetry, and the existence of free water and bound water was discussed in terms of the sulfonation level. The 10 wt % weight loss temperatures of these copolymers were above 470 °C, indicating excellent thermooxidative stability to meet the severe criteria of harsh fuel‐cell conditions. The proton conductivities of the membranes ranged from 3.8 × 10^?2 to 5 × 10^?2 S/cm at 90 °C, depending on the degree of sulfonation. The sulfonated membranes maintained the original proton conductivity even after a boiling water test, and this indicated the excellent hydrolytic stability of the membranes. The methanol permeabilities ranged from 1.65 × 10^?8 to 5.14 × 10^?8 cm²/s and were lower than those of other conventional sulfonated ionomer membranes, particularly commercial perfluorinated sulfonated ionomer (Nafion). The properties of proton and methanol transport were discussed with respect to the state of water in the membranes. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5620–5631, 2005     

核磁共振弛豫方法测定砂岩有效渗透率

在对储油岩芯液体吸附特性研究的基础上，提出了用核磁共振弛豫方法测定岩芯“有效渗透率”的方法，并对实际样品进行了测定分析，获得了较满意的结果. 此方法测定的有效渗透率较传统方法测定的渗透率更接近于实际的储油岩层的渗透率. 有效渗透率的值可以用来进行油藏注水开发效果分析，研究油层剩余油分布. 相信此方法将获得更广泛的应用.     

Cardo聚芳醚酮共聚物的气体透过行为

作者用溶液缩聚方法合成了一系列含Ｃａｒｄｏ侧基的聚芳醚酮（ＰＥＫ—Ｃ）共聚物，研究了氢气、氮气和氧气的透过速率随共聚组成的变化规律，研究结果表明，此系列共聚物的气体透过速率随共聚组成呈Ｓ形关系变化，并且与共聚物的自由体积参数之间有较好的线性相关性     

Gas barrier properties of poly(ε‐caprolactone)/clay nanocomposites: Influence of the morphology and polymer/clay interactions

Poly(ε‐caprolactone)/montmorillonite nanocomposites were prepared maintaining a constant inorganic content with three means: melt blending of poly(ε‐caprolactone) with natural or organomodified clays, in situ polymerization of ε‐caprolactone in the presence of organomodified clays, and initiation of ε‐caprolactone polymerization from the silicate layer with appropriate organomodified montmorillonites and activator. In this last case, the polymer chains were grafted to the silicate layers and it was possible to tune up the grafting density. The presence of clays did not modify the polymer crystallinity. It was shown that the in situ polymerization process from the clay surface improved the clay dispersion. The gas barrier properties of the different composite systems were discussed both as a function of the clay dispersion and of the matrix/clay interactions. The highest barrier properties were obtained for an exfoliated morphology and the highest grafting density. Similar evolution of the permeability and the diffusion coefficients was observed. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 205–214, 2005