Anti-swelling Property Research Articles

Self-Crosslinked MXene (Ti3C2Tx) Membranes with Good Antiswelling Property for Monovalent Metal Ion Exclusion.

A 2D membrane-based separation technique has been increasingly applied to solve the problem of fresh water shortage via ion rejection. However, these 2D membranes often suffer from a notorious swelling problem when immersed in solution, resulting in poor rejection for the monovalent metal ion. The design of the antiswelling 2D lamellar membranes has been proved to be a big challenge for highly efficient desalination. Here a kind of self-crosslinked MXene membrane is proposed for ion rejection with an obviously suppressed swelling property, which takes advantage of the hydroxyl terminal groups on the MXene nanosheets by forming Ti-O-Ti bonds between the neighboring nanosheets via the self-crosslinking reaction (-OH + -OH = -O- + H2O) through a facile thermal treatment. The permeation rates of the monovalent metal ions through the self-crosslinked MXene membrane are about two orders of magnitude lower than those through the pristine MXene membrane, which indicates the obviously improved performance of the ion exclusion by self-crosslinking between the MXene lamellae. Moreover, the excellent stability of the self-crosslinked MXene membrane during the 70 h long-term ion separation also demonstrates its promising antiswelling property. Such a facile and efficient self-crosslinking strategy gives the MXene membrane a good antiswelling property for metal ion rejection, which is also suitable for many other 2D materials with tunable surface functional groups during membrane assembly.

Fluorene-containing poly(arylene ether sulfone nitrile)s multiblock copolymers as anion exchange membranes

A series of novel fluorene-containing poly(arylene ether sulfone nitrile)s (FPESN-m/n) multiblock copolymers bearing 1,2-dimethylimidazole groups (ImFPESN-m/n) were synthesized for preparing anion exchange membranes (AEMs). Bromination rather than chloromethylation was used in this work. The bulky and rigid fluorene groups were introduced to force each chain apart to create large interchain spacing. Strong polar nitrile groups were introduced into the hydrophobic segments with the intention of enhancing the anti-swelling property of the AEMs. The length of fluorene–containing hydrophobic segment was varied to study the structure–property of the AEMs. With the ion groups anchored selectively and densely on the hydrophilic segments, all the AEMs exhibited well-defined hydrophilic/hydrophobic microphase-separated structures. As a result, the AEMs showed high hydroxide conductivities in the range of 35.2–118.3 mS cm−1 from 30 to 80 °C and superb ratios of ionic conductivity to swelling at 80 °C. Furthermore, the AEMs also exhibited good mechanical properties, thermal and alkaline stabilities.

Imidazolium-functionalized carbon nanotubes crosslinked with imidazole poly(ether ether ketone) for fabricating anion exchange membranes with high hydroxide conductivity and dimension stability

Simultaneously improving the hydroxide conduction capacity and anti-swelling property of anion exchange membranes (AEM) is a big challenge in the field of fuel cells. In this work, the poly (vinyl imidazole) functionalized carbon nanotube (PVI@CNT) was synthesized as a dual functional nanofiller and introduced into the imidazole poly(ether ether ketone) (IPEEK) matrix. The imidazolium groups on the PVI@CNT offer additional ion conducting sites to improve the hydroxide conductivity. The imidazolium groups also react with the IPEEK to form a crosslinking structure along the nanotubes, thus ensuring favorable anti-swelling property. The nanohybrid membrane with 15 wt % PVI@CNT (IPEEK/PVI@CNT-15) shows a maximum conductivity of 121 mS cm−1 at 70 °C, 100% relative humidity (RH). Meanwhile, the crosslinking structure suppresses the swelling degree from 42.0% (pristine IPEEK) to 17.8% (IPEEK/PVI@CNT-15). The single H2/O2 fuel cell performance of the membrane electrode assembly (MEA) with IPEEK/PVI@CNT-15 membrane reveals a high power density of 128.7 mW cm−2. Moreover, the incorporation of the PVI@CNT also enhances the alkali stability and the thermal stability of the nanohybrid membranes.

(Invited) Morphological Engineering for Polymer-Based Electrochemical Sensors

Bioelectronic devices incorporating polymeric materials into their active region has recently emerged as a driver for the next-generation sensors and healthcare technologies. A rapidly growing interest in this new application of versatile organic semiconductors and conducting polymers has been witnessed during the last few years, shaping a distinct field of ‘organic (or plastic) bioelectronics’. Low-temperature, large-area processability (e.g. printing), excellent biocompatibility, chemical tunability, and mechanical softness are some of the major reasons that organic-based bioelectronics can be a promising option for unconventional wearable and implantable platforms. However, only a small number of materials have shown promising performances up to now, and the systematic understanding has been lacking on the general processing-structure-property relationships of relevant polymers. In this presentation, a facile solution-based post-deposition morphological modification technique is reported, which successfully applied to the model bioelectronic polymer poly(3,4-ethylenedioxythiophene) polystyrene sulfonate. Besides the intended solid-state structural transformation, a multitude of beneficial effects on the performances of electrochemical transistor devices (a fundamental sensing element in bioelectronics) made of the engineered materials were clearly observed and systematically analyzed by a number of experimental tools. Most importantly, the nanoscale chain re-arrangements and induced long-range crystallinity gave rise to the substantial compositional changes that eventually led to the improved anti-swelling property, larger volumetric capacitance, and unprecedentedly high thermal and environmental stability. It is therefore expected that both the scientific understanding and application potentials underlined in this study will serve as a practical guideline for the development of viable organic bioelectronics technologies.

Ternary thiol-ene photopolymerization for facile preparation of ionic liquid-functionalized hybrid monolithic columns based on polyhedral oligomeric silsesquioxanes

A simple thiol-ene photopolymerization approach was developed for the rapid preparation of ionic liquid-functionalized hybrid monolithic column based on polyhedral oligomeric silsesquioxane (POSS). “One-pot” polymerization was realized in the UV-transparent fused-silica capillary by using octanethiol, 1-allyl-3-methylimidazolium hexafluorophosphate as functional monomers and methacryl-substituted POSS as a crosslinker. The thiol-vinyl-methacrylate ternary system uniquely exhibits a mixed step-chain growth polymerization regime that combining the thiol-ene reaction and free-radical reaction mechanisms, which provides a simple route to prepare novel POSS-based functionalized hybrid monoliths. The pore property, permeability, and electroosmotic flow (EOF) of the hybrid monoliths can be tailored by proper adjustment of the feeding composition and initiation condition. Morphologic and spectroscopic characterizations of monolithic columns clearly indicate that utilization of the photo-initiated approach in thiol-vinyl polymerization can generate a more homogeneous porous structure, smaller domain size and higher column efficiency (53,800–60,300 plates/m for alkylbenzenes) than the thermally-initiated one (32,800–49,300 plates/m). Significant improvements in mechanical stability, anti-swelling property and tailorability of hybrid polymer were achieved in a simple manner, owing to the photopolymerization of rigid nanoscale POSS units and imidazolium-based ionic liquids in ternary thiol-vinyl system for the first time. The resulting hybrid monolith possessed controllable EOFs at pH values from 2 to 10, and showed a multimode separation mechanism in capillary electrochromatography, including π-π interaction, ion exchange, electrophoretic migration, electrostatic and hydrophobic interaction. Satisfactory separation ability was achieved for the analysis of different types of small molecules.

Embedding Ag+@COFs within Pebax membrane to confer mass transport channels and facilitated transport sites for elevated desulfurization performance

In this study, covalent organic frameworks (COFs) are utilized as carriers to immobilize metal ions in facilitated transport membranes for organic solvent separation for the first time. SNW-1, a kind of COFs with high amount of amino groups, were loaded with Ag+ ions and then incorporated into Pebax matrix to prepare hybrid membranes. Under optimal conditions, 48.11 wt% of Ag+ was loaded onto SNW-1 through a facile approach, which greatly intensified the mass transfer of unsaturated penetrant molecules (thiophene) by π-complexation. The channels within SNW-1 decreased the mass transport resistance and imparted the molecular sieving ability. The organic nature of SNW-1 optimized the interfacial affinity between filler and polymer, and rendered appropriate free volume properties. The membranes displayed simultaneously enhanced permeation flux and selectivity in pervaporation gasoline desulfurization. Especially, when the content of Ag+@SNW-1 was 9 wt%, the optimum performance towards thiophene concentration of 1312 ppm under 60 °C, was achieved with permeation flux of 16.35 kg/(m2 h) and enrichment factor of 6.8, which was increased by 78.5% and 30.0%, respectively, compared with pure Pebax membranes. In addition, the anti-swelling property of the membranes was improved and the membranes possessed superior long-term stability. This study demonstrates that COFs are superior carriers to immobilize metal ions within facilitated transport membrane for efficient liquid separation.

A new fracturing material in oil and gas industry

In this study, a novel non-residual fracturing fluid was developed. This fracturing fluid system is crosslinked under acid condition and owns the advantages of fast dissolving, excellent sand carrying ability, non-residual, good anti-swelling property and low damage etc. Experimental results show that this system viscosity can reach 95% of peak viscosity in 3 minutes, the surface tension of the gel breaking liquid is 25 mN/m, the residue content of the gel breaking fluid is 10mg/L, core permeability damage rate less than 15% which greatly reduces the damage to formation and fracture conductivity. The shear viscosity of fracturing fluid for 90min is 260 mPa.s, it has good resistance to high temperature and shearing performance and can meet the requirements of fracturing in tight reservoir. The new fluid was tested in 65 wells in the tight gas and oil reservoir in western China. Oil &gas production after stimulation using the new fluid increased 2-5 times compared with wells in similar locations.

Highly branched side chain grafting for enhanced conductivity and robustness of anion exchange membranes

As a key component of alkali anion exchange membrane fuel cells, the anion exchange membrane (AEM) needs to have high ionic conductivity and good stability. Herein, highly branched side chain grafted polysulfone AEMs are designed and fabricated via macromolecule-initiated atom transfer radical polymerization of chloromethyl styrene. The highly branched side chain results in increased free volume in the AEM. As a result, the membrane shows significantly improved hydroxide conductivity relative to its un-branched counterpart membrane. Furthermore, the highly branched side chain renders the membrane with better anti-swelling property and improved alkaline stability. These results demonstrate that constructing highly branched side chain architecture is an effective strategy for fabricating AEMs with high conductivity and stability.

Layer-by-layer self-assembly of polycation/GO nanofiltration membrane with enhanced stability and fouling resistance

Polyelectrolyte multilayering is a good technique used to fabricate nanofiltration (NF) membranes. However, the stability and fouling resistance of the polyelectrolyte membranes should be improved for industrial application. In this study, graphene oxide (GO) nanosheets were assembled with polycation to form a multilayer on a polyacrylonitrile substrate via a layer-by-layer self-assembly strategy. The migration and rearrangement of the polyelectrolyte chain were restricted because of the confinement effect of a neighboring GO nanosheet layer. Therefore, the anti-swelling property of the polycation/GO multilayer membrane was enhanced, which resulted in a more stable performance. The fouling resistance of the multilayer membrane was also improved because of the anti-fouling capability of the GO nanosheets. The polycation/GO multilayer membrane was used to remove dye from water. During the separation of methyl blue molecule from water at 5 bar, the flux and retention rate of the obtained multilayer membrane could reach 6.42 kg m−2 h−1 bar−1 and 99.2%, respectively. Compared with a pure polyelectrolyte multilayer membrane, the separation performance, stability, and fouling resistance of the polycation/GO membranes were significantly enhanced. The polycation/GO multilayer membrane can be potentially used to fabricate NF membranes because it is cost efficient and GO nanosheets can be produced in a large scale.

Polydimethyl siloxane–graphene nanosheets hybrid membranes with enhanced pervaporative desulfurization performance

A series of polydimethyl siloxane-graphene nanosheets (PDMS-GNS) hybrid membranes were fabricated via physically blending method. In these hybrid membranes, GNS exhibit different orientation and dispersity with the variation of GNS content. An appropriate interfacial structure favoring permeate molecules transport is constructed, which mainly arises from the non-covalent interactions between PDMS and GNS. The mechanical stability, thermal stability and anti-swelling property of the hybrid membranes are simultaneously enhanced. Pervaporative desulfurization performance of PDMS-GNS/PVDE hybrid membranes was investigated utilizing n-octane/thiophene mixture as a model gasoline system. The prepared hybrid membranes show an enhanced permeation flux while maintaining a constant enrichment factor, which should be attributed to the optimized free volume characteristics of the membranes and pi-pi interactions between GNS and thiophene. Especially, when GNS/PDMS mass ratio reaches 0.2 wt%, the membrane shows an optimum desulfurization performance with a permeation flux of 622 kg/(m(2) h) (65.9% higher than that of pure PDMS membrane) and an enrichment factor of 3.58 (similar to that of pure PDMS membrane). Additionally, the effects of GNS content, operation temperature, thiophene content, feed Row rate and operation time on membrane separation performance were investigated systematically. The prepared hybrid membranes may find potential applications in the separation of aromatics-containing mixtures. (C) 2015 Elsevier B.V. All rights reserved.

Fabrication of sulfonated poly(ether ether ketone)-based hybrid proton-conducting membranes containing carboxyl or amino acid-functionalized titania by in situ sol–gel process

Functionalized titania are used as fillers to modify the sulfonated poly(ether ether ketone) (SPEEK) membrane for improved proton conductivity and methanol barrier property. The functionalized titania sol which contains proton conductive carboxylic acid groups or amino acid groups are derived from a facile chelation method using different functional additives. Then the novel SPEEK/carboxylic acid-functionalized titania (SPEEK/TC) and SPEEK/amino acid-functionalized titania (SPEEK/TNC) hybrid membranes are fabricated via in situ sol–gel method. The anti-swelling property and thermal stability of hybrid membranes are enhanced owing to the formation of electrostatic force between SPEEK and titania nanoparticles. The hybrid membranes exhibit higher proton conductivity than plain SPEEK membrane because more proton transfer sites are provided by the functionalized titania nanoparticles. Particularly, the proton conductivity of SPEEK/TNC membrane with 15% filler content reaches up to 6.24 × 10−2 S cm−1, which is 3.5 times higher than that of the pure SPEEK membrane. For methanol permeability, the SPEEK/TNC membranes possess the lowest values because the acid-base interaction between sulfonic acid groups in SPEEK and amino groups in functionalized titania leads to a more compact membrane structure.

Preparation and performance of different amino acids functionalized titania-embedded sulfonated poly (ether ether ketone) hybrid membranes for direct methanol fuel cells

A series of amino acid functionalized titania submicrospheres were synthesized and incorporated into sulfonated poly (ether ether ketone) (SPEEK) to fabricate organic–inorganic hybrid proton exchange membranes. Pristine TiO2 with a uniform particle size of ~200nm were synthesized and functionalized with four kinds of amino acids including oxidized l-cysteine, O-phospho-l-serine, aspartic acid and histidine, designated as TiO2–Scys, TiO2–Pser, TiO2–Asp and TiO2–His, respectively. The effects of amino acid attribute on the membrane properties were investigated. At the filler content of 15wt%, the TiO2–Scys embedded membrane exhibited the highest proton conductivity of about 5.98×10−3Scm−1 (20°C, 100% RH), while the TiO2–His embedded membrane exhibited the lowest conductivity due to the strong acid-base interaction between the basic imidazole groups of histidine and the sulfuric acid groups of SPEEK. The TiO2–Pser embedded membrane exhibited the highest selectivity of 17.10×103Sscm−1. In addition, the methanol crossover of the hybrid membranes was reduced by two folds, and the anti-swelling property and thermal stability of the hybrid membranes were also enhanced.

High-performance sulfonated polyimide/polyimide/polyhedral oligosilsesquioxane hybrid membranes for ethanol dehydration applications

A novel miscible polymer blend of copoly(1,5-naphthalene/3,5-benzoic acid-2,2′-bis(3,4-dicarboxyphenyl)) hexafluoropropanedimide 6FDA-NDA/DABA and its sulfonated polyimide has been investigated as a water-selective layer to develop dual-layer hollow fiber membranes for ethanol dehydration via pervaporation. The resultant fibers display an excellent flux of >3.0kg/m2h. This is possibly ascribed to a good distribution of sulfonic groups in the polymer matrix, the increased hydrophilicity and enlarged d-space induced by sulfonic groups, which are verified by polarized light microscopy (PLM), contact angle measurement, sorption tests and XRD. Three different post-treatment approaches, namely, thermal treatment, PDMS coating and modification with polyhedral oligosilsesquioxane (POSS) were employed to improve the membrane selectivity. Their effects on polymer chain packing, dense skin layer thickness and ethanol dehydration performance have been investigated with the aid of the advanced PALS technique. Thermal treatment can densify the selective layer structure while PDMS coating provides a thin shielding layer to protect the selective layer from feed-induced swelling. More importantly, POSS modification displays as the most effective way to enhance the membrane selectivity due to the anti-swelling property of POSS inorganic nanoparticles, mobility restriction of polymer chains and narrowed d-space in polymer structure. Compared to various membranes in the literature, the newly developed hollow fibers in the present study have superior fluxes of >2.0kg/m2h and good separation factor of >200 for ethanol dehydration. This study may provide useful insights for the exploration of new materials and post-modifications for biofuel separations.

Enhanced anti-swelling property and dehumidification performance by sodium alginate–poly(vinyl alcohol)/polysulfone composite hollow fiber membranes

Abstract Enhanced membrane dehumidification performance was achieved by physically blending sodium alginate (NaAlg) with poly(vinyl alcohol) (PVA). Both flat-sheet homogenous membranes and hollow-fiber composite membranes were prepared and characterized by Fourier transform infrared spectra (FT-IR), X-ray diffraction (XRD), differential scanning calorimetry (DSC), positron annihilation lifetime spectroscopy (PALS). When PVA content was 20 wt.% and 30 wt.%, the blend membranes exhibited lower swelling degree and much higher water/propylene selectivity than both NaAlg and PVA control membranes, resulting from the better-controlled free volume cavity size. In particular, the blend membrane containing 20 wt.% PVA showed the best dehumidification performance for propylene-water mixture. Both high water permeance (>10−2 cm3(STP)/cm2 s cmHg) and high selectivity (infinite big) were acquired for 0.13 wt.% water in feed under optimized operating conditions (temperature: 298 K; feed pressure: 250 kPa; feed flowrate: ≥300 ml/min).

Asymmetric hollow fibers by polyimide and polybenzimidazole blends for toluene/iso-octane separation

Among the various separation technologies available, pervaporation has been regarded as a very promising one for aromatic/aliphatic hydrocarbons separations. Works in the past have already identified many polymers as suitable membrane materials for these targeted separations. As an effort toward practical application, this current work was aimed at the formation of asymmetric polymeric membranes. The best performance achieved in this study has been a separation factor of ∼200 and a flux of ∼1.35 kg/m 2-h in separating toluene/iso-octane (50/50 wt.%) at a downstream pressure of ∼10 mbar. These membranes were fabricated from blends of commercially available polybenzimidazole (PBI) and polyimide Matrimid using dry-jet wet-spinning followed by non-solvent induced phase inversion. Information from DSC and SEM analyses confirmed the molecular miscibility of the two polymers within the range of their weight ratio chosen. The blue shift for the characteristic peak of phthalimide carbonyl group in Matrimid revealed in FTIR evidenced the formation of hydrogen bonding between Matrimid and PBI, which is an important factor helpful for miscibility. From pervaporation performance tests results, it was observed that increasing PBI content gave rise to a higher separation factor for the selective transport of toluene, while total flux was correspondingly reduced. The effect of PBI on separation performance was attributed to its stronger polarity, tighter and more rigid structure, as well as enhanced anti-swelling property. It was also found that a higher spinneret temperature and a longer air-gap have positive influences on the pervaporation performance. Tensile strength test results revealed that all the hollow fibers held reasonable mechanical properties.