Preparation and separation properties of oxalylurea‐bridged silica membranes

Two new bridged alkoxysilanes, bis(triethoxysilylalkyl)‐N,N′‐oxalylureas (alkyl = methyl or n‐propyl), bearing a highly rigid and polar oxalylurea unit in the bridges, were employed as precursors of bridged silica membranes. The gas and water separation performance of the membranes prepared from the precursors using the sol–gel process was investigated. Interestingly, the membrane properties depended on the alkyl chain length. The membrane containing methylene units (alkyl = methyl) was porous and rather hydrophilic but the other with longer propylene units (alkyl = n‐propyl) was non‐porous and more hydrophobic. High H₂/SF₆ gas permeance ratios of 3100 and 1700, and NaCl rejections of 89 and 85% for 2000 ppm aqueous NaCl were obtained using the membranes containing methyl and n‐propyl, respectively. The membrane with alkyl = methyl also showed a high CO₂/N₂ permeance ratio of 20.6 at 50°C. These results indicate the potential applications of the membranes as gas and water separation materials. Copyright © 2015 John Wiley & Sons, Ltd.     

Preparation and characterisation of polyaniline based membranes for gas separation

Transport rates (permeability) and ideal separation factors for several gas pairs through dense polyaniline membranes are reported. The ideal separation factors for all gas pairs tested were found to be independent of the polyaniline membrane thickness whereas the permeability of the single gases showed significant variations. Both dedoped and redoped films (film thickness between 9 and 67 μm) were studied. The highest selectivities α_(A/B) found were 7.6 for the gas pair H₂/CO₂ in the case of the dedoped membrane and 10 for the gas pair H₂/CO₂, 6 for O₂/N₂ and 200 for H₂/N₂ in the case of the redoped membrane. Statistical analysis of a large number of membranes allowed the critical comparison with results obtained by other groups.Comparison with other membrane materials shows that an approximately sixfold enhancement of the respective separation factors is possible for gas pairs containing hydrogen. Similar separation factors are observed for the gas pairs CO₂/O₂, CO₂/N₂ and N₂/O₂.Membranes for which Knudsen diffusion was observed exhibited regularly distributed micropores (400 nm diameter).     

Comparison of methods for characterizing microporous membranes for plasma separation

To design membranes suitable for therapeutic use, the relationship between membrane structure and permeability needs to be studied. In this work, the solute permeability of small tubular membranes for plasma separation was determined by using radioisotope-labeled solutes. Through analysis of data on solute and pure water permeability and on water content, by means of a tortuous pore model that we have proposed, we can obtain pore diameter, surface porosity and tortuosity. Membrane structure was also analyzed by mercury intrusion and scanning electron microscopy, and the results were compared with each other. The mercury intrusion method is unsuitable for the structural analysis of polymer membranes because of the damage and/or expansion resulting from highly elevated pressure. The tortuous pore model is recommended for the elucidation of membrane structure.     

Preparation and properties of novel environment-sensitive membranes prepared by graft polymerization onto a porous membrane

The present work is concerned with the preparation and some properties of novel environment-sensitive membranes. A porous poly (vinylidene fluoride) membrane (pore size 0.22 μm) was pretreated by air plasma; subsequently, hydrophilic monomers were graft polymerized on the treated surface. Since the filtration characteristics of the obtained membranes reflect the configuration of the grafted chains, these can be changed reversibly from ultrafilter to microfilter and vice versa in response to the membrane environment such as pH, solvent composition and ionic species. Grafted chains act as a sensor and a valve to regulate filtration characteristics. The poly(acrylic acid) grafted membrane for example is very sensitive to environmental pH. In the pH region of 1 to 5, the filtration rate sharply decreased with increasing solution pH, the filtration rate at pH 1.4 being about ten times higher than at pH 5.2. Together with this decrease in filtration rate, the membrane gained the ability of ultrafiltration of macromolecular solutes such as dextran (M_w = 2,000,000) and albumin (M_w = 67,000). In the pH region of 5.2 to 7.5, filtration rate and solute rejection did not depend on pH. The pH sensitivity is reversible and reproducible. Because of characteristics such as the drastic alteration in filtration rate and solute separation properties and the quick response to solution conditions, the environment-sensitive membranes developed here may find applications in various areas of membrane technology.     

Ultrahigh throughput beehive-like device for blood plasma separation

We report here a low-cost, rapid-prototyping, and beehive-like multilayer polymer microfluidic device for ultrahigh-throughput blood plasma separation. To understand the device physics and optimize the device structure, the effect of cross-sectional dimension and operational parameter on particle focusing behavior was explored using a single spiral microchannel device. Then, the blood plasma separation performance of the determined channel structure was validated using the blood samples with different hematocrits (HCTs). It was found that a high separation efficiency of 99% could be achieved using the blood sample with an HCT of 0.5% at a high throughput of 1 mL/min. Finally, a multilayer microfluidic device with a novel beehive-like multiplexing channel arrangement was developed for ultrahigh-throughput blood plasma separation. The prototype device could be fabricated within ∼1 hour utilizing the laser cutting and thermal lamination methods. The total processing throughput could reach up to 72 mL/min for 0.5% HCT sample with a plasma separation ratio close to 90%. Our device may hold potentials for the ultrahigh-throughput separation of blood plasma from large volume blood samples for downstream disease diagnosis.     

Reagent-free modification of poly(vinyltrimethylsilane) membranes with low-temperature plasma to improve gas separation properties

Russian Chemical Bulletin -     

Preparation and characterization of copolymerized aminopropyl/phenylsilsesquioxane microparticles

Poly(aminopropyl/phenyl)silsesquioxane (PAPSQ) microparticles with approximately 350 nm diameter were conveniently synthesized from the hydrolytic co-condensation of γ-aminopropyltriethoxysilane (APS) and phenyltriethoxysilane (PTES) in the presence of ethanol and water (EtOH-H₂O) by using tetramethylammonium hydroxide (TMAOH) catalysts. Hybrid compositions of PAPSQ containing both aminopropyl and phenyl groups were confirmed from FT-IR, ²⁹Si CP-MAS NMR, TGA. XRD patterns indicated that a certain ordered structure existed in PAPSQ molecules. Contents of amino groups of PAPSQ were determined by elemental analysis and back titration. Specific surface areas were evaluated through BET method. PAPSQ offers the potential utility as building blocks for diverse and novel organic/inorganic materials.     

Integrated separation of blood plasma from whole blood for microfluidic paper-based analytical devices

Many diagnostic tests in a conventional clinical laboratory are performed on blood plasma because changes in its composition often reflect the current status of pathological processes throughout the body. Recently, a significant research effort has been invested into the development of microfluidic paper-based analytical devices (μPADs) implementing these conventional laboratory tests for point-of-care diagnostics in resource-limited settings. This paper describes the use of red blood cell (RBC) agglutination for separating plasma from finger-prick volumes of whole blood directly in paper, and demonstrates the utility of this approach by integrating plasma separation and a colorimetric assay in a single μPAD. The μPAD was fabricated by printing its pattern onto chromatography paper with a solid ink (wax) printer and melting the ink to create hydrophobic barriers spanning through the entire thickness of the paper substrate. The μPAD was functionalized by spotting agglutinating antibodies onto the plasma separation zone in the center and the reagents of the colorimetric assay onto the test readout zones on the periphery of the device. To operate the μPAD, a drop of whole blood was placed directly onto the plasma separation zone of the device. RBCs in the whole blood sample agglutinated and remained in the central zone, while separated plasma wicked through the paper substrate into the test readout zones where analyte in plasma reacted with the reagents of the colorimetric assay to produce a visible color change. The color change was digitized with a portable scanner and converted to concentration values using a calibration curve. The purity and yield of separated plasma was sufficient for successful operation of the μPAD. This approach to plasma separation based on RBC agglutination will be particularly useful for designing fully integrated μPADs operating directly on small samples of whole blood.     

改性氧化石墨烯膜的制备及其性能研究

为了改善氧化石墨烯(GO)膜的低渗透性和不稳定性,本文采用过氧化氢对GO进行改性后抽滤成膜,并在不同温度下对膜进行热还原.采用超高性能全自动气体吸附仪、透射电镜、扫描电镜、拉曼光谱仪、接触角、X射线衍射等对材料进行结构和形貌表征.分析不同HGO(H2O2改性GO)负载量和不同温度热还原对膜水通量和截留率的影响.在优化条...     

Preparation and characterization of cross-linked Matrimid membranes for CO2/CH4 separation

For preventing plasticization phenomenon, cross-linked Matrimid membranes were prepared. Matrimid membranes were immersed in a solution of 10% (w/v) ethylenediamine or hexamethylenediamine in methanol for preparation of cross-linked membranes. Using a gas separation membrane unit, permeability properties of pristine and modified membranes for pure gases (CO₂ and CH₄) were investigated. CO₂ plasticization effect on permeability properties of the membranes is discussed. Modified membranes indicated smaller values of tensile strength than pristine membranes. Thermal gravimetric analysis showed that thermal resistance of modified membranes increased in a limited temperature range. In general, modified membranes were thermally stable for separation applications. Formation of amide groups in modified membranes was investigated by Fourier transform infrared spectroscopy analysis.     

Permeation and separation properties of polyimide membranes to olefins and paraffins

Pure and mixed gas permeation experiments for olefins and paraffins of C₂ and C₃ were carried out for several polyimide and other polymer membranes at pressures up to 8 atm and temperatures from 308 to 423 K. The olefins were more permeable to the corresponding paraffins due to their preferential diffusion based on the difference in their molecular size. Polyimide prepared from 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) and 2,4,6-trimethyl-1,3-phenylenediamine (TrMPD) displayed relatively high performance: permeability coefficient to propylene, P_C3H6 = 20–40 Barrer (1 Barrer = 1 × 10⁻¹⁰ cm³(STP)/(cm s cmHg)) and ideal separation factor (permeability ratio of pure propylene and propane). α_id(C₃H₆/C₃H₈) = 11 at 323 K and 2 atm. Polyimide from 6FDA and dimethyl-3,7-diaminodiphenylthiophene-5,5-dioxide (DDBT) displayed low permeability and high permselectivity: P_C3H6 = 0.8 Barrer and α_id(C₃H₆/C₃H₈) = 27 at 323 K and 2 atm. Their performance was much better than that of other polymers such as poly(2,6-dimethyl-1,4-phenyleneoxide). For mixed gas permeation, the separation factor was lower by about 40% than the α_id due to the increase in P_C3H8 caused by coexisting propylene.     

Protein adsorption on microporous membranes for plasma separation and its effects on flux decay

The present study elucidates the adsorption characteristics of bovine serum albumin (BSA) on microporous membranes for plasma separation. Based on adso in hydraulic permeability after contact with BSA solutions, the effects of the material and structure of the microporous membranes on adsorption charac resistance increases as BSA solutions are filtered through the microporous membranes. This may result from protein adsorption on the pore walls of the decreases with an increase in BSA concentration and cumulative perfusate volume. The adsorbed amount of BSA and the decreases in filtrate flux are stro and internal structure of the microporous membranes for plasma separation.     

Preparation of methyl methacrylate and glycidyl methacrylate copolymerized nonporous particles

Particles of methyl methacrylate (MMA) and glycidyl methacrylate (GMA) copolymer having narrow size distributions were prepared by the method of dispersion polymerization. Results from the analysis of particle porosity and the correlation of specific surface area with the reciprocal of particle diameter suggest that the prepared particles were nonporous. The particle size was found to decrease from 4.2 to 2.1 μm with increasing the mass ratio of GMA/MMA from 0.1 to 0.75. Polymer particles having an average diameter falling in this range are suitable for being employed as the stationary phase in protein chromatography. The decrease in particle size when GMA was present could be due to the increase in adsorption rate of poly(vinyl pyrrolidone). The oligomer chains that were rich in GMA were more active for adsorbing and grafting PVP, compared with the moiety of MMA. An increase in the GMA/MMA ratio also leaded to a decrease in epoxy‐group density on the particle surface, since the reactivity of GMA was greater than that of MMA. Results of this work suggest that the influence of GMA/MMA mass ratio on the particle size and surface functionality of the nonporous particles was very significant. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1457–1463, 1999     

Preparation, morphologies and properties for flat sheet PPESK ultrafiltration membranes

Flat sheet poly(phthalazinone ether sulfone ketone) (PPESK) ultrafiltration membranes were prepared. The effects of PPESK concentration, solvents, additives and exposing time on the structure and performance of PPESK ultrafiltration membranes were investigated in more detail. The optimal preparation conditions were: 12 wt.% PPESK, NMP/DMAc mixed solvent (mass ratio = 1), 8 wt.% polyethylene glycol 400 (PEG400), 2.5 wt.% LiCl and 5 s exposing time. Under these conditions, the pure water flux and the rejection of γ-globulins were 1139L/m² h and 93.7% at the operation pressure of 0.1 MPa, respectively.

Scanning electron microscope (SEM) micrographs showed that spongy structure could be formed while finger-like structure could be suppressed due to the longer exposing time or higher LiCl concentration.     

Preparation and gas separation properties of zeolite T membrane

Zeolite T membranes were synthesized on tubular porous mullite tubes by hydrothermal synthesis. The membranes selectively permeated carbon dioxide from CO2/CH4 and CO2/N2 mixtures with high separation performances, which were due to combined effects of molecular sieving and competitive adsorption.     

温敏性丙烯腈共聚物纳米纤维膜的制备与性能

采用可逆加成断裂链转移可控/活性聚合方法合成了丙烯腈与N-异丙基丙烯酰胺(NIPAM)的嵌段共聚物,通过调控嵌段聚合反应时间可以获得一系列不同嵌段链长的共聚物,分子量分布在1.3左右.运用静电纺丝技术制备了所合成嵌段共聚物的纳米纤维膜,扫描电镜照片表明纳米纤维膜较为均匀且直径可调.研究了纳米纤维膜表面水接触角与荧光标记牛血清清蛋白的吸附现象,接触角结果证实共聚物纳米纤维膜具有一定的温度响应性,且疏水性嵌段的引入导致响应温度较PNIPAM有所降低;蛋白质吸附结果则表明温度较低时纳米纤维膜表面更亲水,蛋白质吸附较少.所制备的温敏性纳米纤维膜可望用作智能分离与吸附材料.     

Preparation and properties of photochromic bacterial cellulose nanofibrous membranes

The photochromic bacterial cellulose (BC) nanofibrous membranes containing 1′,3′,3′-trimethyl-6-nitrospiro(2H-1-benzopyran-2,2′-indoline) (NO₂SP) were successfully prepared by surface modification of BC nanofibers with spiropyran photochromes, and their physical and photochromic properties were characterized. The FTIR spectra indicated the interaction between BC and NO₂SP which leads to the uniform dispersion of NO₂SP in the nanofibrous membrane. SEM results demonstrated that the introduction of NO₂SP maintains the nanofibrous network structure of BC. UV/vis spectrometry of the resulting BC-NO₂SP revealed that the membranes show reversible photochromic property by changing their color from colorless to pink forming a merocyanine structure upon UV irradiation, and returning back again to colorless spiropyran structure by visible light. The contact angle of the BC-NO₂SP with water was found to be reversibly regulated due to the reversible isomerization of the spiropyran moieties in BC-NO₂SP. The result indicates that the surface modification with spiropyran photochromes expands new applications of BC nanofibers and such photochromic nanofibers with excellent photosensitivity have great potentials for sensitive displays, biosensors and other optical devices.