The Ionic Conductivity of a Nafion® 1100 Series of Proton‐exchange Membranes Re‐cast from Butan‐1‐ol and Propan‐2‐ol

The ionic conductivity of Nafion® 1100 extruded membranes re‐cast from solutions of butan‐1‐ol and propan‐2‐ol is measured in 0.5 mol dm^–3 H₂SO₄ at 295 K, using an immersed, four‐electrode d.c. technique. The general trend is an increasing conductivity for the thicker membranes. Materials which were solution‐cast from butan‐1‐ol yielded the highest conductivity while a series of membranes with lower conductivities (similar to those of an extruded Nafion® 1100 series of membranes) was found using propan‐2‐ol. The conductivity results indicate that membranes manufactured by extrusion and casting from various solvents might have different structures. Differences in the water content and conductivity of the membranes are considered to arise from the impact of processing conditions on the surface and bulk structure of the membranes.     

评估混合气在PDMS膜中渗透性能的操作模型

An operational model is developed to evaluate and predict the permeation performance of mixed gas through poly（dimethylsiloxane） （PDMS） membranes by combining the ideal gas permeation model with the experimental analysis of the mixed gas transport character. This model is tested using the binary and ternary mixed gas with various compositions through the PDMS membranes, and the predicted data of the permeation flux and the compositions of the permeated gas are in good agreement with the experimental ones, which indicates that the operational model is applicable for the evaluation of the permeation performance of mixed gas through PDMS membranes.     

Hemodialysis membrane prepared from cellulose/N‐methylmorpholine‐N‐oxide solution. II. Comparative studies on the permeation characteristics of membranes prepared from N‐methylmorpholine‐N‐oxide and cuprammonium solutions

Two kinds of regenerated cellulose membranes for hemodialysis were prepared from casting solutions of N‐methylmorpholine‐N‐oxide (NMMO) and cuprammonium (denoted NMMO membranes and cuprammonium membranes, respectively). The concentration of cellulose in the casting solution investigated was 6–8 wt %. The permeation characteristics of both membrane series were compared in terms of the ultrafiltration rate (UFR) of pure water, the sieving coefficient (SC) of dextran, and the solute permeabilities of urea, creatinine, and vitamin B₁₂. The UFR and SC of the NMMO membranes were strongly affected by the cellulose concentration of the casting solution, and NMMO was a preferable solvent for the production of cellulose membranes with high performance; the cuprammonium solution gave low‐performance membranes. The pore structures of both types of membranes were estimated with the Hagen–Poiseuille law. The results showed that the NMMO membranes had larger pore radius and smaller pore numbers than the cuprammonium membranes. The differences in the membrane pore structures led to the differences in the performance between the two membrane series. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 333–339, 2003     

Preparation and characterization of photocatalytic titania–alumina composite membranes by sol–gel methods

Titania–alumina composite membranes containing 10 and 20 mol% alumina were prepared by two different sol–gel methods; co-hydrolysis and separately peptized. The samples were characterized by different techniques. XRD results showed that for the composite membranes the anatase to rutile transformation temperature was increased by 200 and 300 °C. According to specific surface area results, alumina effectively increased the specific surface area of composite membranes compared to pure titania membranes. Microstructure of composite supported membranes was considered by scanning electron microscopy and showed a crack-free layer with 1 μm thickness. The photocatalytic activity of composite samples showed that alumina addition up to an optimum amount can slightly affect the photocatalytic activity of titania.     

Thermo‐Responsive Gating Characteristics of Poly(N‐isopropylacrylamide)‐Grafted Membranes

Both hydrophilic Nylon‐6 membranes and hydrophobic poly(vinylidene fluoride) (PVDF) membranes, with a wide range of grafting yields of poly(N‐isopropylacrylamide) (PNIPAM), were prepared using the plasma‐graft pore‐filling polymerization method. The effect of the physical and chemical properties of the substrates on the thermo‐responsive gating characteristics of the PNIPAM‐grafted membranes was investigated experimentally. For both the PVDF and Nylon‐6 membranes, the grafted PNIPAM polymers were found not only on the membranes outer surface, but also on the inner surfaces of the pores throughout the entire thickness of the membrane. The thermo‐responsive gating characteristics of the PNIPAM‐grafted membranes were heavily affected by the physical and chemical properties of the porous membrane substrates. The PNIPAM‐g‐Nylon‐6 membranes exhibited a much larger thermo‐responsive gating coefficient than the PNIPAM‐g‐PVDF membranes. Furthermore, to achieve the largest thermo‐responsive gating coefficient, the corresponding optimum grafting yield of PNIPAM for the PNIPAM‐g‐Nylon‐6 membranes was also larger than that for the PNIPAM‐g‐PVDF membranes.     

Preparation and characterization of monovalent ion‐selective poly(vinyl chloride)‐blend‐poly(styrene‐co‐butadiene) heterogeneous anion‐exchange membranes

New types of composite anion‐exchange membranes were prepared by blending of suspension‐produced poly(vinyl chloride) (S‐PVC) and poly(styrene‐co‐butadiene), otherwise known as styrene–butadiene rubber (SBR), as binder, along with anion‐exchange resin powder to provide functional groups and activated carbon as inorganic filler additive. Also, an ultrasonic method was used to obtain better homogeneity. In solutions with mono‐ and divalent anions, the effect of activated carbon and sonication on the morphology, electrochemical properties and selectivity of these membranes was elucidated. For all solutions, ion‐exchange capacity, membrane potential, permselectivity, transport number, ionic permeability, flux and current efficiency of the prepared membranes initially increased on increasing the activated carbon concentration to 2 wt% in the casting solution and then began to decrease. Moreover, the electrical resistance and energy consumption of the membranes initially decreased on increasing the activated carbon loading to 2 wt% and then increased. S‐PVC‐blend‐SBR membranes with additive showed a decrease in water content and a slight decrease in oxidative stability. Also, these membranes showed good monovalent ion selectivity. Structural images of the prepared membranes obtained using scanning optical microscopy showed that sonication increased polymer‐particle interactions and promoted the compatibility of particles with binder. Copyright © 2010 Society of Chemical Industry     

Recent developments in fuel‐processing and proton‐exchange membranes for fuel cells

In recent years, great progress has been made in the development of proton‐exchange membrane fuel cells (PEMFCs) for both mobile and stationary applications. This review covers two types of new membranes: (1) carbon dioxide‐selective membranes for hydrogen purification and (2) proton‐exchange membranes; both of these are crucial to the widespread application of PEMFCs. On hydrogen purification for fuel cells, the new facilitated transport membranes synthesized from incorporating amino groups in polymer networks have shown high CO₂ permeability and selectivity versus H₂. The membranes can be used in fuel processing to produce high‐purity hydrogen (with less than 10 ppm CO and 10 ppb H₂S) for fuel cells. On proton‐exchange membranes, the new sulfonated polybenzimidazole copolymer‐based membranes can outperform Nafion^® under various conditions, particularly at high temperatures and low relative humidities. Copyright © 2010 Society of Chemical Industry     

Preparation of poly(4‐methyl‐1‐pentene) asymmetric or microporous hollow‐fiber membranes by melt‐spun and cold‐stretch method

Poly(4‐methyl‐1‐pentene) (PMP) hollow fibers were prepared and fabricated into gas separation or microporous membranes by the melt‐spun and cold‐stretched method. PMP resin was melt‐extruded into hollow fibers with cold air as the cooling medium. The effects of take‐up speed and thermotreatment on the mechanical behavior and morphology of the fibers were investigated. Scanning electronic microscope (SEM) photos were used to reveal the geometric structure of the section and surface of the hollow fibers. It was found that the original fiber had an asymmetric structure. A “sandwich” mode was used to describe the formation of this special fine structure. And a series of PMP hollow‐fiber membranes were prepared by subsequent drawing, and it was found that there was a “skin–core” structure on the cross section of these hollow‐fiber membranes. Asymmetric or microporous PMP hollow‐fiber membranes could be obtained by controlling posttreatment conditions. The morphology of these membranes were characterized by SEM, and the gas (oxygen, nitrogen, and carbon dioxide) permeation properties of the membranes was measured. The results indicate that the annealing time of the original fiber and the stretching ratio were the key factors influencing the structure of the resulting membrane. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2131–2141, 2006     

Defektfreie Mixed‐Matrix‐Membranen aus Matrimid® und Aktivkohle für die Gastrennung

In this work the fabrication of new mixed‐matrix membranes (MMMs) of Matrimid® and activated carbon (AC) for gas separation is reported. The aim is the fabrication of membranes that have better gas permeation properties compared to the pristine Matrimid® membranes. The membranes were thermally and morphologically characterized, and the gas transport properties of single gases were estimated by a variety of methods. It has been found that with an increase of the AC content the selectivity remained stable for the different gases despite the marked increase in the effective permeability of the pure gases.     

Density‐based phase‐separation asymmetric polyethylene–poly(dimethyl siloxane) blend membranes: Preparation and properties

A new concept of density‐based phase separation for the preparation of asymmetric membranes from polyethylene (PE) blended with liquid poly(dimethyl siloxane) (PDMS) has been tried. The PE/PDMS membranes were prepared via high‐temperature solution casting. The purpose of incorporating PDMS was to utilize its flexibility, relatively high density in comparison with PE, and dissolution in common solvent for the formation of asymmetric PE/PDMS membranes. The study has been carried out with 1.25, 2.5, 5, and 10% (v/w) loading of PDMS. A host of techniques were used to study morphology of PE/PDMS blend membranes. The membranes show nodular structure on surfaces in contact with solvent vapor environment, whereas the opposite surfaces have smoother texture devoid of nodules. Although differential scanning calorimetric (DSC) melting endotherms indicate enhancement of crystallinity with PDMS addition, chemical etching and subsequent scanning electron microscopic (SEM) observations show increasingly ordered spherulitic pattern on individual nodules with the incorporation of PDMS up to 2.5%. The density of the films also increases with the addition of PDMS as compared to the control. ATR‐FTIR data revealed asymmetric distribution of PDMS in membranes with more PDMS retention toward lower surface of membranes. Membrane cross sections were indicative of graded porosity with increasing pore size toward the bottom surface of membranes. The results were explained in terms of density‐based phase separation.© 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91:2278–2287, 2004     

Development of antifouling polyamide thin‐film composite membranes modified with amino‐cyclodextrins and diethylamino‐cyclodextrins for water treatment

The fouling behavior of polyamide thin‐film composite (TFC) membranes modified with amino‐ and diethylamino‐cyclodextrins (CDs) through an in situ interfacial polymerization process is reported. Modified polyamide TFC membranes exhibited improved hydrophilicity, water permeability, and fouling resistance as compared to the unmodified TFC membranes, while restricting the passage of NaCl salt (98.46 ± 0.5%). The increase in hydrophilicity was attributed to the secondary and tertiary hydroxyl groups of the CDs, which were not aminated. The membranes modified with amino‐CDs had increased surface roughness while the membranes modified with diethylamino‐CDs had smoother surfaces. However, despite the surface roughness of the membranes modified with amino‐CDs, low fouling was observed due to the highly hydrophilic surfaces, which superseded the roughness. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40109.     

Stereoselective Behavior of Nafion® Membranes towards (+)‐α‐Pinene and (−)‐α‐Pinene

α‐Pinene enantiomers were sorbed in Nafion® membranes. The membranes included a commercial extruded Nafion® 115 membrane as well as membranes prepared by casting a Nafion® solution, evaporating the solvent, and a thermal treatment at different temperatures. The microstructure of membranes was studied by small‐angle and wide‐angle X‐ray scattering, and magic‐angle spinning nuclear magnetic resonance spectroscopy. The change of membrane weight during the sorption process was determined with a sorption microbalance. Noticeable differences concerning the sorption behavior of the various membranes could be stated. The sorption of (+)‐α‐pinene and (?)‐α‐pinene in an extruded Nafion® membrane turned out to be rather low.     

MOF‐Based Mixed‐Matrix Membranes in Gas Separation – Mystery and Reality

Microporous additives like nanosized metal‐organic framework (MOF) particles can improve the gas separation performance of polymer membranes. These membranes which consist of added filler particles in a continuous polymer phase are called mixed‐matrix membranes (MMM). While inorganic zeolites and organic polymers do not match well, the preparation of defect‐free MOF‐based MMMs is much easier. However, some problems can also occur during the preparation. Solutions how to avoid them and prepare perfect MMMs are given. In practical gas separation, the selectivity of the MMMs was found to be even higher than predicted by the Maxwell model.     

The preparation of microporous membranes from blends of poly(2,6‐dimethyl‐1,4‐phenylene oxide) and sulfonated poly(2,6‐dimethyl‐1,4‐phenylene oxide)

Poly(2,6‐dimethyl‐1,4‐phenylene oxide) (PPO) is a chemically resistant polymer and, therefore, an attractive material for the formation of membranes. However, membranes of unmodified PPO prepared by an immersion precipitation possess very low hydraulic permeabilities at the filtration processes. The membranes with higher hydraulic permeabilities can be prepared from sulfonated PPO and/or from blends of unsulfonated PPO and sulfonated PPO. In conclusion, the mechanism of the formation of membranes from blends of unsulfonated PPO and sulfonated PPO is suggested. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 161–167, 1999     

A facile synthesis of mixed soft‐segmented poly(urethane‐imide)–polyhedral oligomeric silsesquioxone hybrid nanocomposites and study of their structure–transport properties

The structure–transport properties of mixed soft‐segmented poly(urethane‐imide) (MSPUI) membranes and their microstructures were investigated. Polypropylene glycol, polycaprolactone diol and bis(3‐aminopropyl)‐terminated polydimethylsiloxane were used as the soft segments in the membrane synthesis via a three‐step polymerization reaction. The chemical structures of the MSPUI membranes were characterized using attenuated total reflectance Fourier transform infrared spectroscopy. Morphology and surface properties of the membranes were studied using scanning electron and atomic force microscopy techniques. Surface energy measurements indicated the enrichment of the hydrophobic soft segment in the membranes. The amorphous nature of the polymers was analysed using wide‐angle X‐ray diffraction. The effect of morphology on the permeability and selectivity of the membranes is discussed. Finally, membrane structure–transport property relationships were correlated. © 2013 Society of Chemical Industry     

Regulation of micromorphology and proton conductivity of sulfonated polyimide/crosslinked PNIPAm semi‐interpenetrating networks by hydrogen bonding

A series of novel sulfonated polyimide (SPI)/crosslinked poly(N‐isopropylacrylamide) (cPNIPAm) semi‐interpenetrating polymer networks (semi‐IPNs) were synthesized as the proton exchange membranes for direct methanol fuel cells via in situ polymerization. The micromorphology and properties of the semi‐IPN membranes were characterized. The results indicated that the hydrogen bonds between cPNIPAm and SPI in the semi‐IPN structure were a crucial factor for regulating the micromorphology, proton conductivity and other properties of the semi‐IPN membranes. A more uniform sulfonic ionic cluster distribution was observed in the membrane of SPI‐20‐cPNIPAm with equimolar ratio of sulfonic acid groups and amido bonds, which could provide effective proton transport channels. The SPI‐20‐cPNIPAm exhibited a maximum proton conductivity of 0.331 S cm^?1 at 80 ^oC (relative humidity 100%), an optimal selectivity of 8.01 × 10⁵ S s cm^?3 and an improved fuel cell performance of 72 mW cm^?2 compared with both pristine SPI and other semi‐IPN membranes. The SPI‐20‐cPNIPAm semi‐IPN membranes also retained good mechanical properties and thermal stabilities on the whole. © 2014 Society of Chemical Industry     

Synthesis and morphology of platinum‐coated hollow‐fiber carbon membranes

Hollow‐fiber carbon membranes were prepared and used as support media for a platinum catalyst. The platinum metal was deposited onto the surface of the hollow‐fiber carbon membranes by three different techniques: solution coating with chloroplatinic acid, which is the commonly used technique; vapor deposition, involving the sublimation of the platinum metal; and magnetron sputter coating, the most effective method. The hollow‐fiber carbon membranes coated with a chloroplatinic acid solution were studied with scanning electron microscopy (SEM) and energy‐dispersive X‐ray analysis (EDAX). The platinum coating grew on the surface, unevenly, in the form of small crystals. The percentage of platinum on the surface was too low to be detected by EDAX. The high‐vacuum evaporation coating of the membranes with platinum was also studied with both SEM and EDAX. Again, because of the low percentage of platinum, EDAX did not reveal any platinum on the surfaces of the membranes. The magnetron sputter coating of platinum onto the membranes was performed and studied with SEM. The thickness of the coated platinum could be varied through variations in the coating time. The cavities observed in the micrographs were formed during the coating operations by the presence of dust particles on the membranes. An SEM micrograph of a hollow‐fiber carbon membrane, produced from a polyacrylonitrile‐based precursor, spun with a low amount of dimethyl sulfoxide in the bore fluid, and coated with platinum, showed a skin on the outside and a porous elongated structure inside the skin. The distance between the inner and outer skins contained fingerlike pores of various sizes. The largest pores were found near the inside skin, whereas the smallest pores were next to the outside skin. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1051–1058, 2003     

Synthesis and characterization of polymer‐filled nonwoven membranes

Polymer‐filled nonwoven membranes were prepared by filling the open pores of nylon nonwovens with poly(2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid) (PAMPS). PAMPS was synthesized via radical polymerization and crosslinked to prevent its dissolution in water. PAMPS‐filled nylon nonwoven membranes showed enhanced dimensional stability and mechanical properties when compared with PAMPS membranes without nonwovens. The conductivities of PAMPS‐filled nylon nonwovens were slightly lower than those of PAMPS membranes. Compared with PAMPS membranes without nonwoven hosts, both linear and crosslinked PAMPS‐filled nylon nonwoven membranes exhibited lower vapor permeabilities for water, methanol, acetone, and dimethyl methylphophonate (DMMP). In addition, crosslinked PAMPS‐filled nonwoven membranes presented high permselectivity on DMMP over water, which is critical for chemical protection application. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Construction strategies of self-cleaning ceramic composite membranes for water treatment

Ceramic membranes have received much popularity due to their high mechanical strength, satisfactory acid/alkali resistance, and long-term stability. However, ceramic membranes are also inevitably fouled by contaminates during the membrane separation process. Therefore, construction strategies of anti-fouling ceramic membranes are a main topic in current research. In this work, we review a better anti-fouling ceramic membrane, which is named “self-cleaning” membrane and membrane process. Date to now, there are four main strategies to construct self-cleaning ceramic membranes: 1) porous piezoelectric ceramic membranes; 2) photo-catalytic ceramic membrane; 3) electrochemical ceramic membranes and 4) self-cleaning ceramic membrane surface. Self-cleaning ceramic membranes can in-situ remove and decompose the pollutants on the membrane surface and recover the water permeance that exhibits a great potential to treat industrial wastewater without backwashing or other methods. The detailed membrane fabrication period, mechanism and important case studies are reported in this review. Self-cleaning ceramic membrane is expected to be next-generation anti-fouling ceramic membrane material for continuous water treatment. It is a first review work that systematically concluded all the strategies for self-cleaning ceramic membranes that can be an important reference in ceramic or membrane fields.     

Wäßrige Flüssigmembranen — Stand der Entwicklung

Aqueous liquid membranes – State of the art. Use of emulsion liquid membranes with an aqueous membrane phase is a promising technique for the separation of hydrocarbons, if distillation is difficult or impossible. Intensive investigations on aqueous membranes during the past five years have increased our knowledge of the mass transfer mechanism which exploits different solubilities and diffusivities for the separation of hydrocarbons. The influence of the most important process parameters on the selectivity of the separation and on an overall mass transfer coefficient, serving as a measure of the mass transfer rate, are discussed. Possible applications and further developments are presented.