The influence of sulfonated polyethersulfone (SPES) on surface nano-morphology and performance of polyethersulfone (PES) membrane

In this research, firstly sulfonation of polyethersulfone (PES) was carried out and then polyethersulfone (PES)/sulfonated polyethersulfone (SPES) blend membranes were prepared with phase inversion induced by immersion precipitation technique. polyvinylpyrrolidone (PVP, 2 wt% concentration) was added in the casting solution as pore former. SPES was characterized by FT-IR and UV-visible spectra, ion exchange capacity and swelling ratio. The characterization of SPES polymer indicates that the sulfonic acid groups were produced on PES polymer. Also, the prepared PES/SPES blend membranes were characterized by contact angle, AFM, SEM and cross-flow filtration for milk concentration. The contact angle measurements indicate that the hydrophilicity of PES membrane is enhanced by increasing the SPES content in the casting solution. The SEM and AFM images show that the addition of SPES in the casting solution results in a membrane with larger surface pore size and higher sub-layer porosity. The mean pore size of the membrane increased from 98 nm for PES membrane to 240 and 910 nm for 50/50 and 0/100 PES/SPES blend membranes, respectively. The pure water flux and milk water permeation through the prepared membranes are increased by blending PES with SPES. Moreover, the protein rejection of PES/SPES blend membranes was lower than PES membrane.     

Strengthen the performance of sulfonated poly(ether ether ketone) as proton exchange membranes with phosphonic acid functionalized carbon nanotubes

Nanocomposite polymers based on phosphonic acid functionalized carbon nanotubes (CNT-POH) and sulfonated poly(ether ether ketone) (SPEEK) have been fabricated and employed as highly efficient proton exchange membranes. CNT-POH were synthesized through the grafting of carbon nanotubes (CNT) with diethylphosphatoethyl triethoxysilane and subsequent acidification of phosphate to phosphonic acid ligands. Incorporating CNT-POH into SPEEK matrix improves the proton conductivity at different temperatures and relative humidity, which can be attributed to the homogeneous dispersion of highly hydrophilic phosphonic acid groups and the formation of proton transport channels in the membrane. The methanol permeability of the composite membranes is also decreased, owing to the increased tortuosity of the methanol transport channel. The CNT in SPEEK matrix also enhance the dimensional stability and mechanical property remarkably. Consequently, this phosphonic acid functionalized CNT/SPEEK composite membrane (SPEEK-POH) is a potential candidate for application in direct methanol fuel cells (DMFC).     

Synthesis and properties of side-chain-type ion exchange membrane PEEK-g-StSO3Na for bipolar membranes

Side-chain-type ion exchange membranes (PEEK-g-StSO₃Na) were prepared by grafting poly (ether ether ketone) (PEEK) containing propenyl groups with sodium sulfonic styrene (StSO₃Na) and KH570. PEEK was synthesized by the aromatic nucleophilic polycondensation reaction of 4,4′-difluorobenzophenone, bisphenol A and diallylbisphenol A. The synthesized copolymers with the -SO₃Na group on the side chain of polymers possessed high molecular weights. The cross-linking reaction was carried out through a sol-gel reaction of the trimethoxysilane group. The copolymer membranes exhibited excellent mechanical properties due to their aromatic structure extending through the backbone and flexible StSO₃Na aliphatic chains. The ion exchange capacities (IECs) of the membranes ranged from 2.27 to 2.50 mmol g⁻¹ and the water content ranged from 107.2 to 126.1%, with both parameters increasing with StSO₃Na grafting degree. The H⁺ permeability of copolymer membranes increased with increasing IEC, reaching value above 0.3056 mol/L at 2 h, which is higher than that of Nafion^® 117 at the same measurement condition. They displayed reasonably high H⁺ permeability due to the higher acidity of benzoyl sulfonic acid group, the larger interchain spacing, which is available for water occupation, and the lower AC impedance of the bipolar membrane.     

Investigation of the role of benzimidazole-based model compounds on thermal stability and anhydrous proton conductivity of sulfonated poly(ether ether ketone)

The present work shows a strategy to apply hydrogen bond connected benzimidazole compounds for improvement of proton conductivity and thermal stability of sulfonated poly(ether ether ketone) (SPEEK). A series of benzimidazole derivatives, i.e., mono-, di- and trifunctional benzimidazole, are applied to study the role of their packing structures related to the specific properties for SPEEK in being a proton exchange membrane. The benzimidazole-based compounds significantly increase the thermal stability of the SPEEK and, at the same time, improve proton conductivity of SPEEK under anhydrous condition at temperatures higher than 80 °C. The investigation of the structural effect of the benzimidazole based model compounds implies that the trifunctional benzimidazole molecule is the most effective compound to improve the thermal stability and the proton conductivity of SPEEK as compared to mono- and difunctional ones.     

Crystallinity and dielectric relaxations in semi-crystalline poly(ether ether ketone)

The Maxwell-Wagner-Sillars (MWS) relaxation is studied for semi-crystalline polymers poly (ether ether ketone) (PEEK), in the range 20 Hz-1 MHz and temperature varying from 80 to 330 °C. The parameter is the crystallization condition in the case of PEEK, which is a semi-crystalline polymer considered as a particulate composite. The relaxation found in the semi-crystalline polymers above the α relaxation of the PEEK is ascribed to the trapping of conductive carriers at the interface between crystalline lamellae and the amorphous matrix. The study of PEEK microstructure is based on differential calorimetry and X-rays diffraction. Two lamellae populations have been detected, that depends on the crystallization temperature and its duration. The crystallinity rate is increasing with crystallization temperature and duration. In dielectric studies, the use of the electric modulus instead of permittivity allows us to minimize the ionic conduction and then leads to the appearance of the interfacial relaxation. According to our measurements, the crystallinity rate is not the main factor of the interfacial relaxation intensity, which also depends on the nature and degree of perfection of the lamellae.     

Sulfonated Aromatic Polymers and Organically Modified Montmorillonite Nanocomposite Membranes for Fuel Cells Applications

Aromatic polymers, such as sulfonated poly(2,6-dimethyl-1,4-phenylene oxide) (SPPO), sulfonated poly(ether ether ketone) (SPEEK), and sulfonated poly(ether sulfone) (SPES), at the optimum degrees of sulfonation (DS), are suggested and evaluated as alternatives to Nafion for direct methanol fuel cells (DMFCs) applications. To reduce the methanol cross-over, which decreases the efficiency of the cell, organically modified montmorillonite nanoclays (OMMT) were added at 1 wt% to the sulfonated matrices with the optimum DS. The X-ray diffraction (XRD) patterns of nanocomposite membranes proved that the nanoclay layers were exfoliated. The proton conductivity and methanol permeability of the membranes, as well as the ion-exchange capacity (IEC), were measured. The selectivity parameter, ratio of proton conductivity to methanol permeability, was identified at 25°C for the nanocomposite membranes and the results were compared with Nafion117. Finally, the DMFC performance tests were investigated at 70°C and 5 M methanol feed for the manufactured nanocomposite polyelectrolyte membranes (PEMs). The SPEEK-based nanocomposite membrane showed the highest maximum power density in comparison with Nafion 117 and SPES and SPPO nanocomposite membranes. The results indicated that the nanocomposite membranes were promising PEMs for DMFC applications.     

Optimization of polymeric host composition for polymer-based electrophosphorescent devices

We have demonstrated an optimized polymeric host material comprising a blend of poly(9-vinylcarbazole) (PVK) and a fluorescent polymer for a highly efficient electrophosphorescence system. Although the chemical compatibility between the blue-emitting-fluorescent polymer and iridium complex, tris[2-phenylpyridine]iridium(III) (Ir-(ppy)₃), is very poor, efficient energy transfers from the blended host to the Ir complex was observed when a small amount of blue-emitting-fluorescent polymer was added to the PVK matrix. The device showed a maximum external quantum efficiency at 5 wt% blue-emitting-fluorescent polymer and 8 wt% Ir complex doping concentrations.     

Effect of PMMA on crystallization behavior and hydrophilicity of poly(vinylidene fluoride)/poly(methyl methacrylate) blend prepared in semi-dilute solutions

Films of poly(vinylidene fluoride) (PVDF)/poly(methyl methacrylate) (PMMA) blend were derived from a special procedure of casting semi-dilute solutions. Hydrophilic character and crystallization of PVDF were optimized by variation of PMMA concentration in PVDF/PMMA blends. It was found that a PVDF/PMMA blend containing 70 wt% PMMA has a good performance for the potential application of hydrophilic membranes via thermally induced phase separation. The films presented β crystalline phase regardless of PMMA content existed in the blends. Thermal analysis of the blends showed a promotion of crystallization of PVDF with small addition of PMMA which induced larger lamellar thickness of PVDF, leading to the largest spherulitic crystal of PVDF (10 wt% PMMA) is about 8 μm. SEM micrographs illustrated no phase separation occurred in blends, due to the high compatibility between PVDF and PMMA.     

Effect of chemical etching on the Cu/Ni metallization of poly (ether ether ketone)/carbon fiber composites

Poly(ether ether ketone)/carbon fiber composites (PEEK/Cf) were chemical etched by Cr₂O₃/H₂SO₄ solution, electroless plated with copper and then electroplated with nickel. The effects of chemical etching time and temperature on the adhesive strength between PEEK/Cf and Cu/Ni layers were studied by thermal shock method. The electrical resistance of some samples was measured. X-ray photoelectron spectroscopy (XPS) was used to analyze the surface composition and functional groups. Scanning electron microscopy (SEM) was performed to observe the surface morphology of the composite, the chemical etched sample, the plated sample and the peeled metal layer. The results indicated that CO bond increased after chemical etching. With the increasing of etching temperature and time, more and more cracks and partially exposed carbon fibers appeared at the surface of PEEK/Cf composites, and the adhesive strength increased consequently. When the composites were etched at 60 °C for 25 min and at 70-80 °C for more than 15 min, the Cu/Ni metallization layer could withstand four thermal shock cycles without bubbling, and the electrical resistivity of the metal layer of these samples increased with the increasing of etching temperature and time.     

Preparation and characterization of Tb and Tb(sal)3·nH2O doped PC:PMMA blend

Tb doped polycarbonate:poly(methyl methacrylate) (Tb-PC:PMMA) blend was prepared with varying proportions of PC and PMMA. Thermal and spectroscopic properties of the doped polymer have been investigated employing Fourier Transform Infrared (FTIR) absorption and differential scanning calorimetric (DSC) techniques. PC:PMMA blend (with 10 wt% PC and 90 wt% PMMA) shows better miscibility. Optical properties of the dopant Tb³⁺ ions have been investigated using UV-vis absorption and fluorescence excited by 355 nm radiation. It is seen that luminescence intensity of Tb³⁺ ion depends on PC:PMMA ratio and on Tb³⁺ ion concentration. Concentration quenching is seen for TbCl₃·6H₂O concentration larger than 4 wt%. Addition of salicylic acid to the polymer blend increases the luminescence from Tb³⁺ ions. Luminescence decay curve analysis affirms the non-radiative energy transfer from salicylic acid to Tb³⁺ ions, which is identified as the reason behind this enhancement.     

Adhesion of epoxy-thermoplastic and polysulfone-LCP matrices to fibres

This work investigated the adhesion strength τ of the joints of polymer blends with fibres. Blends of polysulfone with LC-polyether and epoxy resin (based on DGEBA) with polysulfone, polyetherimide and poly(arylene ether ketone) were taken as matrices. Steel wire, polyamide (nylon-6) and glass fibres were used as substrates. The adhesion strength was determined by the 'pull-out' technique. It was found that incorporation of LCP into polysulfone and incorporation of thermoplastics into epoxy matrix resulted in non-additive relationships between the adhesion strength and modifier (LCP or thermoplastic) content C. In the case of epoxy-polysulfone, epoxy-polyetherimide and polysulfone-LCP matrices, such τ-C dependencies were described by curves showing a maximum. Optimal (maximal) adhesion strength of the blend/fibre joints was obtained at 10 wt% of polysulfone, 15 wt% of polyetherimide and poly(arylene ether ketone) in epoxy resin and 2–5 wt% of LC-polyether in polysulfone. Possible mechanisms of the interface strength enhancement are discussed.     

Biocompatibility of polypropylene non-woven fabric membrane via UV-induced graft polymerization of 2-acrylamido-2-methylpropane sulfonic acid

This work described the graft polymerization of a sulfonic acid terminated monomer, 2-acrylamido-2-methylpropane sulfonic acid (AMPS), onto the surface of polypropylene non-woven (NWF PP) membrane by O₂ plasma pretreatment and UV-induced photografting method. The chemical structure and composition of the modified surfaces were analyzed by FTIR-ATR and XPS, respectively. The wettability was investigated by water contact angle and equilibrium water adsorption. And the biocompatibility of the modified NWF PP membranes was evaluated by protein adsorption and platelet adhesion. It was found that the graft density increased with prolonging UV irradiation time and increasing AMPS concentration; the water contact angles of the membranes decreased from 124° to 26° with the increasing grafting density of poly(AMPS) from 0 to 884.2 μg cm⁻², while the equilibrium water adsorption raised from 5 wt% to 75 wt%; the protein absorption was effectively suppressed with the introduction of poly(AMPS) even at the low grafting density (132.4 μg cm⁻²); the number of platelets adhering to the modified membrane was dramatically reduced when compared with that on its virgin surface. These results indicated that surface modification of NWF PP membrane with AMPS was a facile approach to construct biocompatible surface.     

Preparation and dual microwave-absorption properties of carboxylic poly(arylene ether nitrile)/Fe3O4 hybrid microspheres

The carboxylic poly(arylene ether nitrile)/Fe₃O₄ hybrid microspheres were prepared via solvothermal method. The carboxylic poly(arylene ether nitrile) (PEN-COOH) was introduced into the Fe₃O₄ microspheres by chemisorption with mass content up to 15% as defined by infrared spectra and thermal gravimetric analysis. The hybrid sphere is of hierarchical polymer-inorganic microstructure as observed by transmission electron microscopy. The microwave-absorption of the sample owns a shifting peak and a special immobilized peak with the variation of absorber thickness from 3 to 5 mm. Maximum microwave-absorption of the product is capable of over −30 dB in the range of 10-12 GHz. By proposed equivalent filter circuit model, the immobilized peak was attributed to the ordered nanostructure where the Fe₃O₄ nanocrystals were isolated by PEN-COOH. The product has the potential to be applied as microwave absorber with high microwave-absorption, good dispersibility and robust polymer-inorganic interfacial adherence.     

Preparation and characterization of asymmetric polyethersulfone and thin-film composite polyamide nanofiltration membranes for water softening

In this research, two types of nanofiltration membranes were prepared and evaluated for water softening. Their nanofiltration performance was evaluated by cross-flow filtration using NaCl (1 g/l) and MgSO₄ (1 g/l) solution at 5 and 10 bar, 25 °C and 10 l/min. The morphological studies were performed with SEM and AFM instruments. In addition, the hydrophilicity of membranes was examined by contact angle measurements. In the first type, asymmetric polyethersulfone (PES) nanofiltration membranes were prepared using phase inversion induced by immersion precipitation technique. Different components such as polyvinylpyrrolidone (PVP), polyethyleneglycole (PEG), acrylic acid and Triton X-100 were used as additive in the PES casting solution, which lead to the formation of new asymmetric nanofiltration membranes. Two concentrations of PES (20 and 25 wt%) and two different non-solvents (pure water and mixture of water (80 vol.%) and IPA (20 vol.%)) were used for preparing asymmetric nanofiltration membranes. The morphological studies showed that the membranes prepared with non-solvent containing 20 vol.% IPA have smoother surface and smaller pores in surface and sub-layer compared to membranes prepared with pure water as non-solvent. The flux was decreased when higher polymer concentration and mixture of water and IPA were employed for membrane formation. However, NaCl and MgSO₄ rejections were improved. In the second type, thin-film composite polyamide nanofiltration membrane was fabricated using interfacial polymerization of 1,3-phenylenediamine (PDA) with trimesoyl chloride (TMC). A rough and dense film was formed on the PES support membrane by interfacial polymerization. The water permeability of composite membrane was 7 and 21 kg m⁻² h⁻¹ at 5 and 10 bar, respectively. Moreover, the rejection to the MgSO₄ as divalent salt (85 and 90%) was high compared to the NaCl as monovalent salt (64 and 67%).     

用纳米压痕法分析溶剂对聚醚醚酮(PEEK)力学性能的影响

Poly (ether ether ketone)(PEEK) is a high-performance semi-crystalline thermoplastic polymer.Exposure of the polymeric surface to solvents can have a strong effect like softening/swelling of polymeric network or dissolution.In this study,nano-indentation analysis was performed to study the effect of acetone on the surface mechanical properties of PEEK using different exposure time.The experiments were performed with a constant loading rate (10 nm/s) to a maximum indentation displacement (1000 nm).A 30-second hold segment was included at the maximum load to account for any creep effects followed by an unloading segment to 80% unloading.The indentation hardness and the elastic modulus were computed as a continuous function of the penetration displacement in the continuous stiffness mode (CSM) indentation.The experimental data showed that the peak load decreased from ~5.2 mN to ~1.7 mN as exposure time in solvent environment increased from 0 to 18 days.The elastic modulus and the hardness of PEEK samples also displayed a decreasing trend as a function of exposure time in the solvent environment.Two empirical models were used to fit the experimental data of hardness as a function of exposure time which showed a good agreement with the experimental values.     

Ultraviolet irradiation induced changes in the surface of phenolphthalein poly(ether sulfone) film

Changes in surface characteristics of phenolphthalein poly(ether sulfone) (PES-C) film induced by ultraviolet (UV) irradiation were investigated. The surface properties of the pristine and irradiated films were studied by attenuated total-reflection FTIR (FTIR-ATR), X-ray photoelectron spectroscopy (XPS), contact angle measurements and atomic force microscopy (AFM). It was found that photooxidation degradation took place on the sample surface after irradiation and the oxygen content in the surface increased as evidenced by FTIR-ATR and XPS results. The water contact angle of the irradiated films decreased with increasing irradiation time, which was ascribed to the increased polarity of the surface induced by photooxidation. The etching of ultraviolet irradiation induced the roughening of PES-C surface after irradiation with its root-mean-square roughness (RMS) determined by AFM increased from 2.097 nm before irradiation to 7.403 nm in the area of 25 μm × 25 μm.     

Ionic conductivity and electrochemical stability of poly(methylmethacrylate)-poly(ethylene oxide) blend-ceramic fillers composites

The role of inorganic ceramic fillers namely nanosized Al₂O₃ (15-25 nm) and TiO₂ (10-14 nm) and ferroelectric filler SrBi₄Ti₄O₁₅ (SBT CIT) (0.5 μm) synthesized by citrate gel technique (CIT) on the ionic conductivity and electrochemical properties of polymer blend 15 wt% PMMA+PEO₈:LiClO₄+2 wt% EC/PC electrolytes were investigated. Enhancement in conductivity was obtained with a maximum of 0.72×10⁻⁵ S cm⁻¹ at 21 °C for 2 wt% of SrBi₄Ti₄O₁₅ (SBT CIT) composite polymer electrolyte. The lithium-ion transport number and the electrochemical stability of the composite polymer electrolytes at ambient temperature were analyzed. An enhancement in electrochemical stability was observed for polymer composites containing 2 wt% of SrBi₄Ti₄O₁₅ (SBT CIT) as fillers.     

Porous PVdF-HFP/P123 electrolyte membrane containing flexible quasi-solid-state dye-sensitized solar cells produced by the compression method

Flexible quasi-solid-state dye-sensitized solar cells (DSSCs) with porous poly(vinylidenefluoride-co-hexafluoropropylene) (PVdF-HFP)/polyethylene oxide-co-polypropylene oxide-co-polyethylene oxide (P123) electrolyte membranes were fabricated and their photocurrent–voltage (I–V) characteristics are studied. Flexible TiO₂ photoelectrodes were prepared using the compression method and porous PVdF-HFP/P123 membranes, by the nonsolvent-induced phase inversion technique. To activate the electrolyte membrane, the membrane was immersed in liquid-state electrolyte. Increased compression pressure improved the interconnection between TiO₂ nanoparticles, enhancing the photovoltaic performances of the flexible liquid-state DSSCs to a maximum of 3.92% efficiency. Meanwhile, the overall pore structure of the PVdF-HFP/P123 membranes was controlled by varying the blend ratio of P123 to PVdF-HFP. Membranes higher in P123 content gave larger pores and pore volume, increasing the electrolyte uptake of the porous membrane, and thus the ionic conductivity of the electrolyte membrane as well. The photovoltaic characteristics of the flexible quasi-solid-state DSSCs containing a porous PVdF-HFP/P123 electrolyte membrane showed a maximum at 50 wt% P123 content, which gave a short-circuit current density (J_sc) value of 7.28 mA/cm², an open-circuit voltage (V_oc) of 0.67 V, a fill factor (FF) of 0.61 and an energy conversion efficiency (η) of 2.98%. Furthermore, the device designed in this study showed good durability compared to those based on liquid-state electrolyte.     

Study of the influence of the acrylic acid plasma parameters on silicon and polyurethane substrates using XPS and AFM

XPS and AFM have been used to investigate surface modifications produced by acrylic acid (AA) vapor plasma treatment of silicon (Si)(1 0 0) substrates and polyurethanes (PUs) membranes. XPS analyses of Si and PUs treated substrates at low plasma power (5-20 W) revealed the formation of a thin film on the surfaces, which chemically resembles the poly(acrylic acid) film conventionally synthesised. No signal of the Si substrate could be seen under these low plasma power applications on silicon. However, when the plasma power is higher than 30 W one can clearly see XPS silicon signatures. AFM measurements of silicon substrates treated with AA plasma at low power (5-20 W) showed the formation of a thin polymer film of about 220-55 nm thickness. Further, applications of high plasma power (30-100 W) displayed a marked difference from low plasma modifications and it was found sputtering of the silicon substrate. Pervaporation results of AA plasma treated PUs membranes revealed that the selectivity for the separation of methanol from methyl-t-butyl ether is higher at 100 W and 1 min treatment time, than the other conditions studied. This last finding is discussed concerning the surface modifications produced on plasma treated silicon substrates and PU membranes.     

Photoionization mass spectrometry and modeling studies of the chemistry of fuel-rich dimethyl ether flames

Reaction paths are identified for dimethyl ether (DME) combustion using modeling of new data from fuel-rich DME flat flames. A molecular-beam flame-sampling photoionization mass spectrometer, employing VUV synchrotron radiation, is applied to the measurement of mole fractions for 21 flame species in low-pressure premixed fuel-rich (Φ = 1.2, 1.68) DME/oxygen/argon flat flames. This approach is capable of resolving and identifying isomers and other flame species of near equal masses with ionization thresholds that differ by as little as 0.1 eV. The measurements agree well with flame modeling predictions, using a recently revised high-temperature DME kinetic mechanism, which identify reaction paths quite analogous to alkane combustion. They further reveal the presence of ethyl methyl ether, a molecule previously unobserved in flames and not included in present flame models.