Composite hollow fiber membranes for CO2 capture

Composite hollow fibers membranes were prepared by coating poly(phenylene oxide) (PPO) and polysulfone (PSf) hollow fibers with high molecular polyvinylamine (PVAm). Two procedures of coating hollow fibers outside and respective inside were investigated with respect to intrinsic PVAm solution properties and hollow fibers geometry and material.The influence of operating mode (sweep or vacuum) on the performances of membranes was investigated. Vacuum operating mode gave better results than using sweep because part of the sweep gas permeated into feed and induced an extra resistance to the most permeable gas the CO₂. The composite PVAm/PSf HF membranes having a 0.7–1.5 μm PVAm selective layer, showed CO₂/N₂ selectivity between 100 and 230. The selectivity was attributed to the CO₂ facilitated transport imposed by PVAm selective layer. The CO₂ permeance changed from 0.006 to 0.022 m³(STP)/(m² bar h) in direct correlation with CO₂ permeance and separation mechanism of the individual porous supports used for membrane fabrication. The multilayer PVAm/PPO membrane using as support PPO hollow fibers with a 40 nm PPO dense skin layer, surprisingly presented an increase in selectivity with the increase in CO₂ partial pressure. This trend was opposite to the facilitated transport characteristic behaviour of PVAm/porous PSf. This indicated that PVAm/PPO membrane represents a new membrane, with new properties and a hybrid mechanism, extremely stable at high pressure ratios. The CO₂/N₂ selectivity ranged between 20 and 500 and the CO₂ permeance from 0.11 to 2.3 m³(STP)/(m² bar h) depending on the operating conditions.For both PVAm/PSf and PVAm/PPO membranes, the CO₂ permeance was similar with the CO₂ permeance of uncoated hollow fiber supports, confirming that the CO₂ diffusion rate limiting step resides in the properties of the relatively thick support, not at the level of 1.2 μm thin and water swollen PVAm selective layer. A dynamic transfer of the CO₂ diffusion rate limiting step between PVAm top layer and PPO support was observed by changing the feed relative humidity (RH%). The CO₂ diffusion rate was controlled by the PPO support when using humid feed. At low feed humidity the 1.2 μm PVAm top layer becomes the CO₂ diffusion rate limiting step.     

多层非线性渗流耦合系统的特征分数步差分方法

对多层非线性渗流耦合系统提出适合并行计算的特征分数步差分格式, 利用变分形式、能量方法、粗细网格配套、分片双二次插值、差分算子乘积交换性、高阶差分算子的分解、先验估计的理论和技巧, 得到收敛性的最佳阶的l₂误差估计. 该方法已成功的应用到多层油资源评估的生产实际中.     

Multilayer modeling of radiative transfer by SLW and CW methods in non-isothermal gaseous medium

Non-isothermal gaseous medium is modeled using the multilayer approach, breaking the one-dimensional system into a series of isothermal layers. Spectral integration of the radiative transfer equation (RTE) is performed for the spectral line weighted-sum-of-gray-gases and cumulative wavenumber approaches to modeling the spectral nature of the gas radiation. An exact analytical solution of RTE is obtained for the layers with both black and gray walls. Predictions show high accuracy, even with surprisingly few layers.     

Temperature effect on optical properties of the cuticle of Lucilia sericata

Optical properties of the spinal cuticle taken from the species of Lucilia sericata are studied by the reflectance measurements and their structural properties by scanning electron microscopy. The multilayer structure of the cuticle has been confirmed from the scanning electron micrographs. The temperature sensitivity of the multilayer structure is documented by the modification of optical properties in a heating process. The heating process and the local heating using the focused laser beam causes the local changes of the optical properties what is finally demonstrated by the structural color shift of the reflected spectra.     

Multilayer adsorption from multicomponent liquid mixtures on solid surfaces

Multilayer adsorption of multicomponent liquid mixtures on homogeneous and heterogeneous solid surfaces is discussed. Heterogeneity effects of the adsorbent surface have been taken into account in calculation of mole fractions of the components in the first adsorbed layer. The model calculations, illustrating multilayer and heterogeneity effects, have been performed for adsorption of ternary liquid mixtures.

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Mehrschicht-Adsorption von flüssigen Mehrkomponentenmischungen auf festen Oberflächen

Zusammenfassung Es wird die Mehrschichtadsorption auf homogenen und heterogenen Oberflächen diskutiert. Bei der Berechnung der Molbrüche der Komponenten der ersten adsorbierten Schicht wurden Heterogenitäts-Effekte berücksichtigt. Die Modellrechnungen wurden an ternären flüssigen Mischungen vorgenommen.

     

Preparation of electrically conducting cellulose fibres utilizing polyelectrolyte multilayers of poly(3,4-ethylenedioxythiophene):poly(styrene sulphonate) and poly(allyl amine)

The primary goal with this work is to create electrically conductive cellulose fibres, this has been done to explore possible new applications for fibre based material. This research uses various methods to create polyelectrolyte multilayers (PEMs) on bleached softwood fibres and on SiO₂ model surfaces, by sequentially treating these materials with poly(3,4-ethylenedioxythiophene):poly(styrene sulphonate) (PEDOT:PSS) and poly(allyl amine) (PAH). Paper sheets were then produced from the PEM-modified pulp and evaluated in terms of tensile strength, adsorbed amount of polymer, and electrical conductivity. To evaluate the influence of fibre charge on the measured paper properties, pulps of two different initial fibre charge densities were prepared via carboxymethylation. Because of the bluish colour of PEDOT:PSS, the build-up of PEM could be easily followed, since the fibres grew increasingly darker blue throughout the modification sequence. The conductivity of the fibre network increased by 2−3 orders of magnitude when the pulp of a higher fibre charge density was used. This suggests that it is more important to create a fibrous network with a high fibre-fibre joint strength and a large total joined area in the sheet rather than to maximize the adsorbed amount of PEDOT:PSS. A difference in conductivity could also be noted depending on the polyelectrolyte adsorbed in the outer layer, PAH lowered the conductivity compared to PEDOT:PSS. Evaluating the mechanical properties revealed that the use of PEDOT:PSS reduces the tensile strength of the paper. When five double layers had been adsorbed onto the carboxymethylated sample in which PEDOT:PSS formed the outer layer, calculations indicated a 25% decrease in tensile strength compared to that of reference material without PEMs. ESEM studies indicate that PEM treatment produces a significantly changed and somewhat smoother fibre surface.     

Analysis of Dynamic and Thermodynamic Adsorption of Nanoparticles on Solid Surfaces by Dark‐Field Light Scattering Measurements

We have constructed a dark‐field light scattering microscope using a very low‐cost digital camera to investigate the adsorption of gold nanoparticles (AuNPs) on four different substrates at various pH values. The substrates used are glass, polycarbonate (PC), poly(dimethylsiloxane) (PDMS), and poly(methyl methacrylate) (PMMA). The coverage of AuNPs on hydrophobic substrates such as PDMS is greater than that on hydrophilic substrates like glass. The adsorption and aggregation of AuNPs on a particular substrate increased upon decreasing the pH (from 9.0 to 4.0). A greater coverage percentage of AuNPs, but less aggregation, occurs on glass treated with poly(diallyldimethylammonium) (PDDA) than on bare glass. The scattering intensity increases upon increasing the number of layers of adsorbed AuNPs on glass that was treated sequentially with AuNPs and PDDA. When compared to UV‐Vis absorption, dark‐field microscope provides greater sensitivity and qualitative surface information.     

多层介质的转移矩阵及其在声子晶体中的应用

引入四维波矢的概念,推导出弹性波斜入射到多层介质系统时的转移矩阵以及透射系数和反射系数。利用这些公式计算了纵波和横波正入射到一维掺杂声子晶体时纵波和横波的透射系数。得出:当纵波正入射时,透射波中纵波在一定频率范围内出现了禁带,并且在禁带的中心频率处出现了缺陷模。当横波正入射时也有相同的结果。     

Coulomb bare interactions in inhomogeneous 4-layer graphene structures

We investigate Coulomb bare interactions in 4-layer graphene systems, taking into account the inhomogeneity of dielectric environment. By solving Poisson equation in momentum space, 16 elements of Coulomb potential tensor have been formed with analytical expressions. The formulae illustrate that Coulomb bare interactions in inhomogeneous 4-layer graphene system differ noticeably from those in homogeneous one. Nevertheless, both intra- and interlayer Coulomb potentials become independent with dielectric constants of contacting media, but they are decided by those of dielectric layer surrounding the system in long wavelength approximation. Besides, numerical results demonstrate that Coulomb bare interactions decrease considerably with the increase in carrier density in graphene sheets as well as their separated distance. In all investigations, the inhomogeneity of dielectric background should not be neglected for improvement in the model.     

The transport current redistribution between the core layers on the models of HTS cables

The multilayer conductors with insulated and non-insulated layers are analyzed. The space–time current redistributions between the layers of the conductor are investigated for the next parameters: values of electric resistance at the current leads, transverse contact electric resistance between the layers, the model length, time, the conductor dimension, the current—its peak value, the change law and the ramp of the total current input. Most of the published test results for short (from 1 to 10 m) conductor models do not reflect the true current distribution of the real long length cable conductors. The criterion of experimental model constructions and, in particular, the calculation of its minimum length are presented. The calculations demonstrate the electromagnetic processes in real cable conductors.