Synthesis and characterization of sulfonated polyimide membranes for direct methanol fuel cell

The sulfonated polyimide (SPI) membranes for direct methanol fuel cell (DMFC) were synthesized with 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA), 2,2′-benzidinedisulfonic acid (BDSA), 4,4′-oxydianiline (ODA) through classical two-step methods: (1) preparation of sulfonated poly(amic acid) (SPAA) precursors with different sulfonation levels by controlling the molar ratio of BDSA to ODA, and (2) thermal imidization of the SPAA films. The chemical structure and the imidization from SPAA membranes were characterized by FT-IR with temperature, and the sulfonation levels were determined by elemental analysis. The thermal stability of the membranes was also characterized by TGA. From water uptake and small angle X-ray scattering (SAXS) experiments for different sulfonation levels, it was found that the number of water clusters in SPI membranes increased as the water uptake of membranes increased, but the size of water cluster was not changed with the sulfonation levels. The proton conductivity and the methanol permeability of SPI membrane showed a sudden leap like a percolation phenomenon around 35 mol% of sulfonation level. The SPI membranes exhibited relatively high proton conductivity and extremely low methanol permeability, and showed the feasibility of suitable polymer electrolyte membranes (PEM) for DMFC.     

Direct methanol–hydrogen fuel cell: The mechanism of functioning

At low air flow rate the active area of a direct methanol fuel cell splits up into galvanic and electrolytic domains: the first one generates current, while the second consumes it to convert methanol to hydrogen. Recent experiments [A.A. Kulikovsky, H. Schmitz, K. Wippermann, Electrochem. Solid State Lett. 10 (2007) B126] suggest that hydrogen can permeate towards the galvanic domain and contribute to current production there. Here we perform analysis of potential distribution in a cell. The analysis shows that between galvanic and electrolytic domains forms the transition region, which can operate as a hydrogen cell. This confirms the conjecture made in the cited paper.     

Sorption and diffusion of methanol and water in PVDF‐g‐PSSA and Nafion® 117 polymer electrolyte membranes

Sorption and diffusion properties of poly(vinylidene fluoride)‐graft‐poly(styrene sulfonic acid) (PVDF‐g‐PSSA) and Nafion® 117 polymer electrolyte membranes were studied in water/methanol mixtures. The two types of membranes were found to have different sorption properties. The Nafion 117 membrane was found to have a maximum in‐solvent uptake around 0.4 to 0.6 mole fraction of methanol, while the PVDF‐g‐PSSA membranes took up less solvent with increasing methanol concentration. The proton NMR spectra were recorded for membranes immersed in deuterated water/methanol mixtures. The spectra showed that the hydroxyl protons inside the membrane exhibit resonance lines different from the resonance lines of hydroxyl protons in the external solvent. The spectral features of the lines of these internal hydroxyl groups in the membranes were different in the Nafion membrane compared with the PVDF‐g‐PSSA membranes. Diffusion measurements with the pulsed field gradient NMR (PFG‐NMR) method showed that the diffusion coefficient of the internal hydroxyl groups in the solvent immersed Nafion membrane mirrors the changes in the diffusion coefficients of hydroxyl and methyl protons in the external solvent. For the PVDF‐g‐PSSA membranes, a decrease in the diffusion coefficient of the internal hydroxyl protons was seen with increasing methanol concentration. These results indicate that the morphology and chemical structure of the membranes have an effect on their solvent sorption and diffusion characteristics. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 3277–3284, 2000     

Synthesis and characterization of novel sulfonated naphthalenic polyimides as proton conductive membrane for DMFC applications

To prepare proton conductive membrane for direct methanol fuel cells (DMFC), a novel sulfonated aromatic diamine monomer, 1,4-bis(4-amino-2-sulfonic acid-phenoxy)-benzene (DSBAPB) was synthesized and characterized by ¹H NMR and FT-IR. Then a series of sulfonated polyimides (SPIs) were prepared from DSBAPB with 1,4,5,8-naphthalene tetracarboxylic dianhydride (NTDA) and a non-sulfonated diamine, 4,4′-oxydianiline (ODA) via one-step high-temperature polymerization method. The sulfonation degree of the SPIs can be controlled by changing the mole ratio of sulfonated monomer to non-sulfonated monomer. The obtained SPI membranes exhibit desirable proton conductivity ranged from 7.9 × 10⁻³ to 7.2 × 10⁻² S cm⁻¹ and low methanol permeability of less than 2.85 × 10⁻⁷ cm² s⁻¹. Furthermore, the hydrolysis stability of the obtained SPIs is better than the BDSA based SPIs caused by the flexible structure.     

Separation of 2-butanol–water mixtures by pervaporation through PVA–NYL 66 blend membranes

Blend membranes of poly(vinyl alcohol) (PVA) and nylon 66 (NYL) were synthesized and crosslinked with glutaraldehyde (GA) and assessed for their suitability in dehydrating 2-butanol by pervaporation (PV). These blends were subjected to sorption studies to determine the extent of interaction and degree of swelling in pure liquids as well as binary mixtures. Wide-angle X-ray diffraction (WAXD) and thermal gravimetric analysis (TGA) were carried out to investigate changes in crystallinity and thermal stability, respectively. The effect of experimental parameters such as feed water concentration, permeate pressure and barrier thickness on membrane flux and selectivity was evaluated. The membranes were found to have good potential for breaking the azeotrope of 27.6 wt.% water with a flux of 3.07 kg/m² h 10 μm and selectivity of 26.5. Selectivity was found to improve with decreasing feed water concentration and increasing membrane thickness, whereas opposite trends were observed in case of flux. Higher permeate pressure caused a reduction in both flux and selectivity. These effects were clearly elucidated.     

Surface redox polymerized SPEEK–MO2–PANI (M = Si, Zr and Ti) composite polyelectrolyte membranes impervious to methanol

We reported sulfonated poly(ether ether ketone) (SPEEK, 61% degree of sulfonation)–metal oxides (MO₂:SiO₂, TiO₂ and ZrO₂)–polyaniline composite membranes. Metal oxides were incorporated into the swelled SPEEK membrane by sol–gel method and cured by thermal treatment. SPEEK–metal oxide membranes surfaces were modified with polyaniline (PANI) by a redox polymerization process. It was observed that water retention capacity of membrane was increased and methanol permeability was reduced due to synergetic effect of metal oxides and surface modification with polyaniline. These composite membranes showed extremely low methanol permeability (1.9–1.3 × 10⁻⁷ cm² s⁻¹), which was lower than till reported values either for SPEEK–metal oxide or SPEEK/PANI membranes. Relatively high selectivity parameter (SP) values at 343 K of these membranes, especially S–SiO₂–PANI and S–TiO₂–PANI, indicated their great advantages over Nafion117 (N117) membrane for targeting on moderate temperature applications due to the synergetic effect of MO₂ and PANI in SPEEK matrix. S–TiO₂–PANI and N117 showed comparable cell performance in direct methanol fuel cell (DMFC).     

New polar silane–PEO polyester complexes as polymer electrolytes

Trifunctional carbosilanes containing hydroxy and cyano groups have been synthesized in good yields and incorporated into polyether-based electrolytes. The new linear and cross-linked modified PEOs have been characterized by DSC and conductivity measurements. The effect of silane content, the length of the PEO block, glycerol concentration, and temperature on glass transition temperature and conductivity of lithium salts complexes of these materials has been evaluated. The new materials showed improved conductivity (∼ 10⁻⁵ S cm⁻¹) at ambient temperatures compared with unmodified polyethers. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1093–1106, 1998     

Supercritical carbon dioxide treated Nafion 212 commercial membranes for direct methanol fuel cells

Supercritical carbon dioxide (Sc-CO₂) thermal treatment to enhance performance of Nafion 212 (NR212) commercial membranes for direct methanol fuel cells (DMFCs) is described. It is shown that the microstructure of NR212 membranes is re-organized after the Sc-CO₂ treatment, and then the performance of NR212 membranes is improved. Specifically the thinner NR212 membranes after the Sc-CO₂ treatments have higher proton conductivity and better capacity of barrier to methanol crossover compared with the thicker Nafion 117 membranes. It is demonstrated that the DMFC performance of the Sc-CO₂ treated NR212 membranes is better than that of Nafion 117 membranes.     

直接甲醇燃料电池中的膜性能比较

制备了磺化聚醚醚酮(SPEEK)和磺化酚酞型聚醚砜(SPES-C)两种质子交换膜,考察了其质子导电和阻醇性能.实验发现,两种新型质子交换膜具有一定的化学稳定性和质子电导率,尤其在高温下两种新膜的质子电导率与Nafion膜接近.两种新膜的甲醇透过系数要比Nafion膜的低1～2个数量级.分别以两种新型膜和Nafion115膜为电解质制备了直接甲醇燃料电池膜电极,讨论了膜材料的性能对直接甲醇燃料电池性能的影响.结果表明,膜材料的阻醇性越好,电池的开路电压越高;膜的电导率越高,在较高电流密度区域内电池的性能越好.     

Impact behavior of sugarcane bagasse waste–EVA composites

The impact performance of chopped bagasse–EVA matrix composites is evaluated and compared with the behavior of bagasse filled PP and PE matrix composites and wood-based materials. The volume fraction and size of the chopped bagasse used as filler was varied. The experimental results show that the incorporation of bagasse strongly reduces the deformation capacity of EVA polymer. The reduction of the deformation capacity of the composites was also inferred by solid-state NMR relaxation analysis. The impact strength was independent of the bagasse size, but varied with the volume fraction. As a function of the volume fraction it was shown that the mechanical performance of bagasse–EVA composites could be tailored to reproduce the behavior of wood-based particle boards.     

Sandwich‐Structured Graphene–Nickel Silicate–Nickel Ternary Composites as Superior Anode Materials for Lithium‐Ion Batteries

We report the synthesis of sandwich‐structured graphene–nickel silicate–Ni ternary composites by using the solvothermal method followed by a simple in situ reduction procedure. The composites show an interesting structure with graphene sandwiched between two layers of well‐dispersed Ni nanoparticles (NPs) anchored on ultrathin nickel silicate nanosheets. These ternary composites exhibit enhanced performance as anode materials owing to the synergistic effect between the graphene matrix and electrochemically inert Ni nanoparticles, an effect that holds promise for the design and fabrication of other advanced electrode materials.     

Liquid–liquid equilibria for pseudoternary systems: isooctane–benzene–(methanol + water)

Liquid–liquid equilibrium data are presented for the pseudoternary systems isooctane–benzene–(90 mass% methanol + 10 mass% water) at 298.15 K and isooctane–benzene–(80 mass% methanol + 20 mass% water) at 298.15 and 308.15 K, under atmospheric pressure. The experimental tie-line data obtained define the binodal curve for each one of the studied systems which depending on the amount of water present show type I or type II liquid–liquid phase diagrams. In order to obtain a general view of the effect of water on the partitioning of methanol and hence on the size of the two-phase region we have also determined experimentally ‘isowater’ tolerance curves for the system isooctane–benzene–methanol at 298.15 K, hence the tie-line data were also obtained for the ternary system. The experimental tie-line data for the four systems studied were correlated with the NRTL and UNIQUAC solution models obtaining a very good reproduction of the experimental behaviour.     

Annealing‐induced increase of permeability and amorphous‐phase mobility in an ethylene–vinylacetate copolymer

The 50% increased permeability after annealing of semicrystalline poly(ethylene/vinylacetate) containing 3 mol % vinylacetate is linked to increased mobility in the amorphous phase, as identified by line‐narrowing of ¹H wideline nuclear magnetic resonance (NMR) spectra and by reduced cross‐polarization efficiency in ¹³C NMR. Other morphological parameters, such as crystallinity, measured as 30 to 35% by differential scanning calorimetry (DSC) and NMR, are hardly changed by annealing. Small‐angle X‐ray scattering and NMR studies, using spin diffusion as well as T_1ρ and T₁ relaxation, detected only a small increase in crystallite thickness. The annealing‐induced enhancement in segmental mobility in the amorphous regions corresponds to a temperature shift of about 10 K, from which an increase of the motional rate by a factor of 2 is estimated, and which can account for the enhancement in the permeability. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2774–2780, 2001     

A New Approach for in vitro Imaging of Breast Cancer Cells by Anti‐Metadherin Targeted PVA‐Pyrene

Poly(vinyl alcohol)‐pyrene‐anti‐metadherin (PVA‐Py‐(Anti‐MTDH)), a novel antibody based water soluble probe containing both fluorescent and target sites in the structure for in vitro imaging of breast cancer cells is reported here. Since breast cancer cells have an excess of MDTH protein expressed on the surface, a PVA‐Py prepared by “Click chemistry” approach is targeted by Anti‐MTDH antibody and applied to the MCF‐7 cell line. After characterization, the designed architecture was evaluated in terms of cell incorporation efficiency and compared with a non‐targeted structure (PVA‐Py). Atomic force microscopy (AFM) and fluorescence microscopy images of cells after incubation of the probe molecules were also obtained to monitor the interaction of the probes with the cancerous cells.

     

Hartmann–Hahn 2D‐map to optimize the RAMP–CPMAS NMR experiment for pharmaceutical materials

Cross polarization–magic angle spinning (CPMAS) is the most used experiment for solid‐state NMR measurements in the pharmaceutical industry, with the well‐known variant RAMP–CPMAS its dominant implementation. The experimental work presented in this contribution focuses on the entangled effects of the main parameters of such an experiment. The shape of the RAMP–CP pulse has been considered as well as the contact time duration, and a particular attention also has been devoted to the radio‐frequency (RF) field inhomogeneity. ¹³ C CPMAS NMR spectra have been recorded with a systematic variation of ¹³ C and ¹H constant radiofrequency field pair values and represented as a Hartmann‐Hahn matching two‐dimensional map. Such a map yields a rational overview of the intricate optimal conditions necessary to achieve an efficient CP magnetization transfer. The map also highlights the effects of sweeping the RF by the RAMP–CP pulse on the number of Hartmann–Hahn matches crossed and how RF field inhomogeneity helps in increasing the CP efficiency by using a larger fraction of the sample. In the light of the results, strategies for optimal RAMP–CPMAS measurements are suggested, which lead to a much higher efficiency than constant amplitude CP experiment. Copyright © 2012 John Wiley & Sons, Ltd.     

1H and 13C NMR assignments of new oligo‐bipyridine–phenanthroline hybrids as potential precursors of helicate complexes

A series of oligo‐bipyridine–phenanthroline hybrids, a new class of potential model ligands, were synthesized and their ¹H and ¹³C NMR spectra assigned. Copyright © 2002 John Wiley & Sons, Ltd.     

Acid–base polyimide blends for the application as electrolyte membranes for fuel cells

The synthesis and characterization of new acid–base polymer blend membranes for the use in polymer electrolyte membrane fuel cell is presented in this paper. A novel polymeric base is synthesized from 1,4,5,8-naphthalenetetracarboxylic dianhydride, 2-bis [4-(4-aminophenoxy)phenyl] hexafluoropropane and diaminoacrydine hemisulfate where the diaminoacrydine hemisulfate contribute the tertiary nitrogen groups to the polyimide backbone. This base polyimide is blended with a polyimide having sulfonic acid group in the main chain. The sulfonated polyimide is synthesized from 1,4,5,8-naphthalene-tetracarboxylic dianhydride (NTDA), 4,4′-diaminobiphenyl 2,2′-disulfonic acid (BDSA), 2-bis [4-(4-aminophenoxy)phenyl] hexafluoropropane (HFBAPP). Various polyimide blends having different molar ratio of sulfonic acid group and acrydine group are synthesized and they are characterized for thermal stability, ion exchange capacity, water uptake, hydrolytic stability and proton conductivity. All the sulfonated polyimides have good thermal stability and exhibited three-step degradation pattern. With the increase in polymeric base content, IEC decreased as AB-0% (2.0640) > AB-10% (2.0058) > AB-20% (1.8792) > AB-30% (1.5686) > AB-40% (1.2670) > AB-50% (1.1690) > AB-75% (0.9098) and water uptake decreased as AB-0% (34.06%) > AB-10% (32.82%) > AB-20% (24.01%) > AB-30% (20.31%) > AB-40% (12.86%) > AB-50% (9.25%) > AB-75% (8.37%). Proton conductivity of the acid–base polyimide blends at 90 °C are AB-0% (0.197) > AB-10% (0.124) > AB-20% (0.122) > AB-30% (0.088) > AB-40% (0.080) > AB-50% (0.034) > AB-75% (0.025). Polyimide blends showed higher hydrolytic stability than the pure acid polyimide. Between the polyimide blends the hydrolytic stability increased with increase in the base polymer content which is attributed to the increase in ionic crosslink density which reduces the polymer swelling and hence the mechanical stability of the membrane increases.     

Blend membranes of Nafion/sulfonated poly(aryl ether ketone) for direct methanol fuel cell

Sulfonated poly(aryl ether ketone) (sPAEK) synthesized by LG Chem. was confirmed by FT-IR. To estimate the thermal stability, glass transition temperature and decomposition temperature were investigated. They showed that sPAEK had good thermal properties. The proton conductivity, methanol permeability and water uptake of sPAEK were also measured. Nafion/sulfonated poly(aryl ether ketone) composite membranes were prepared by blending two materials. The blend ratios of sPAEK and Nafion were 2:1, 3:1, 5:1, and 7:1. The blend membranes showed phase separated morphology since they became immiscible during the solvent evaporation process. Due to the differences in specific gravity and solvent concentration profile during the solvent evaporation process, the upper region had lower Nafion volume fraction with smaller domains and the lower region had higher Nafion volume fraction with larger domains. Mechanical properties such as the stress at break, yield stress, Young's modulus, and elongation at break were measured. The sPAEK had better mechanical properties than Nafion. The mechanical properties increased with increasing sPAEK content. Proton conductivity and methanol permeability of the blend membranes were lower than those of Nafion. Both decreased with decreasing Nafion content. Since the methanol permeability of sPAEK was lower than that of Nafion, sPAEK acted as the methanol barrier. Water uptake of sPAEK was higher than that of Nafion.     

Target Visualization by MRI Using the Avidin/Biotin Amplification Route: Synthesis and Testing of a Biotin–Gd‐DOTA Monoamide Trimer

To design efficient targeting strategies in magnetic resonance (MR) molecular imaging applications, the formation of supramolecular adducts between (strept)avidin ((S)Av) and tribiotinylated Gd‐DOTA‐monoamide complexes (DOTA=1,4,7,10‐tetraazacyclododecane‐N,N′,N′′,N′′′‐tetraacetic acid) was explored. Two compounds based on the trivalent core of tris(2‐aminoethyl)amine each containing three biotin molecules and one ( L1 ) or three ( L2 ) DOTA‐monoamide (DOTAMA) ligands were synthesized. In these tribiotinylated derivatives the biotins are spaced far enough apart to allow the formation of the supramolecular adduct with the protein and to host the chelating units in between the (S)Av layers. Size exclusion HPLC analyses indicated complete formation of very high molecular weight polymers (>2 MDa) with (S)Av in solution. A ¹H NMR spectroscopy relaxometric study on the obtained polymeric adducts showed a marked increase of the relaxivity at 35–40 MHz as a consequence of the lengthening of the tumbling time due to the formation of Gd‐chelates/(S)Av polymers. The most efficient Gd₃ L2 /(S)Av polymeric system was used for a test in cell cultures. The target is represented by a neural cell adhesion molecule (NCAM), which is overexpressed in Kaposi’s sarcoma cells and tumor endothelial cells (TEC) and that is efficiently recognized by a biotinylated tetrameric peptide (C3d‐Bio). In vitro experiments showed that only cells incubated with both C3d‐Bio and Gd₃ L2 /SAv polymer were hyperintense with respect to the control. Relaxation rates of cell pellets incubated with Gd₃ L2 /SAv alone were not significantly different from the untreated cells demonstrating the absence of a specific binding.     

Characterization of PVdF-HFP/Nafion/AlO[OH]n composite membranes for direct methanol fuel cell (DMFC)

Poly-(vinylidene fluoride-hexafluoropropylene) (PVdF-HFP)/Nafion ionomer/aluminum oxy hydroxide nanocomposite membranes were prepared by phase inversion technique. The resultant membranes were subjected to protonic conductivity, methanol permeability, infra-red and thermogravimmetric analysis. The infra-red spectroscopic measurements revealed the presence of sulfonic acid groups in the composite membranes. The thermal stability and ionic conductivity of the polymer membranes have been greatly varied upon the addition of AlO[OH]_n. Although the PVDF-HFP/Nafion/AlO[OH]_n composite membranes have moderate protonic conductivity it has lower methanol permeability and may be considered as a candidate for DMFC applications.