PVA-PSSA Membrane with Interpenetrating Networks and its Methanol Crossover Mitigating Effect in DMFCs

A membrane with interpenetrating networks between poly(vinyl alcohol) (PVA) and poly(styrene sulfonic acid) (PSSA) coupled with a high proton conductivity is realized and evaluated as a proton exchange membrane electrolyte for a direct methanol fuel cell (DMFC). Its reduced methanol permeability and improved performance in DMFCs suggest the new blend as an alternative membrane to Nafion membranes. The membrane has been characterized by powder X-ray diffraction, scanning electron microscopy, time-modulated differential scanning calorimetry, and thermogravimetric analysis in conjunction with its mechanical strength. The maximum proton conductivity of 3.3×10−2 S/cm for the PVA–PSSA blend membrane is observed at 373 K. From nuclear magnetic resonance imaging and volume localized spectroscopy experiments, the PVA–PSSA membrane has been found to exhibit a promising methanol impermeability, in DMFCs. On evaluating its utility in a DMFC, it has been found that a peak power density of 90 mW/cm2 at a load current density of 320 mA/cm2 is achieved with the PVA–PSSA membrane compared to a peak power density of 75 mW/cm2 at a load current density of 250 mA/cm2 achievable for a DMFC employing Nafion membrane electrolyte while operating under identical conditions; this is attributed primarily to the methanol crossover mitigating property of the PVA–PSSA membrane.

A new mixed-matrix membrane for DMFCs

A new mixed-matrix membrane based on stabilized phosphotungstic acid (PTA) incorporated to chitosan (CS)-hydroxy ethyl cellulose (HEC) for application in direct methanol fuel cells (DMFCs) is reported. Membranes are characterised using Fourier Transform Spectroscopy (FTIR), Thermo-Gravimetric Analysis (TGA), Scanning Electron Microscopy (SEM) and their mechanical properties are evaluated. The PTA content in the CS-HEC blend and its influence on proton conductivity, water/methanol sorption, and methanol cross-over in the DMFC is studied. The DMFC with 3 wt. % stabilized PTA-CS-HEC mixed-matrix membrane delivers peak power-density of 58 mW/cm(2) at a load current-density of 210 mA/cm(2) with a lower methanol cross-over than that observed for a DMFC operating with a Nafion membrane electrolyte.

Modified-Pore-Filled-PVDF-Membrane Electrolytes for Direct Methanol Fuel Cells

The polyvinylidene fluoride (PVDF) membrane is modified by the chemical etchant-route employing a sodium naphthalene charge-transfer complex followed by impregnation with Nafion ionomer or polyvinyl alcohol (PVA)-polystyrene sulfonic acid (PSSA) polymeric blend solutions by a dip-coating technique to form pore-filled-membrane electrolytes for application in direct methanol fuel cells (DMFCs). The number of coatings on the surface-modified PVDF membrane is varied between 5 and 15 and is found to be optimum at 10 layers both for Nafion and PVA-PSSA impregnations for effective DMFC performance. Hydrophilicity of the modified-membrane electrolytes is studied by determining average contact angle and surface-wetting energy. Morphology of the membranes is analyzed by a cross-sectional scanning electron microscope. The modified PVDF membrane electrolytes are characterized for their water-methanol sorption in conjunction with their mechanical properties, proton conductivity, and DMFC performance. Air permeability for the modified membranes is studied by a capillary-flow porometer. Methanol crossover flux across modified-PVDF-membrane electrolytes is studied by measuring the mass balance of methanol using a density meter. DMFCs employing membrane electrode assemblies with the modified PVDF membranes exhibit a peak power-density of 83 mW/cm(2) with Nafion impregnation and 59 mW/cm(2) for PVA-PSSA impregnation, respectively. Among the membranes studied here, stabilities of modified-pore-filled PVDF-Nafion and PVDF-PVA-PSSA membranes with 10-layers coat are promising for application in DMFCs. (C) 2010 The Electrochemical Society. DOI: 10.1149/1.3518774] All rights reserved.

Electron spin resonance absorption in organic metal polyaniline and its blend with PMMA

The electron spin resonance absorption in the synthetic metal polyaniline (PANI) doped with PTSA and its blend with poly(methylmethacrylate) (PMMA) is investigated in the temperature range between 4.2 and 300 K. The observed line shape follows Dyson's theory for a thick metallic plate with slowly diffusing magnetic dipoles. At low temperatures the line shape become symmetric and Lorentzian when the sample dimensions are small in comparison with the skin depth. The temperature dependence of electron spin relaxation time is discussed. (C) 1999 Elsevier Science Ltd. All rights reserved.

Synthesis and vesicle formation from hybrid bolaphile/amphiphile ion-pairs. Evidence of membrane property modulation by molecular design

Four new hybrid (bolaphile/amphiphile) ion-pairs were synthesized. Electron microscopy indicated that each of these forms bilayer membranes upon dispersion in aqueous media. Membrane properties have also been examined by differential scanning calorimetry, microcalorimetry, temperature-dependent fluorescence anisotropy measurements, and UV-vis spectroscopy. The T-m values for the vesicular 1, 2, 3, 4, and 5 were 38, 12, 85, 31.3, and 41.6 degrees C, respectively. Interestingly the T-m values for 1 and 3 were found to depend on their concentration. The entrapment of small solute and the release capability have also been examined to demonstrate that these bilayers form enclosed vesicles. X-ray diffraction of the cast films has been performed to understand the nature and the thickness of these membrane organizations. The membrane widths ranged from 33 to 47 Angstrom. Finally, the above observations have been analyzed in light of the results obtained from molecular modeling studies. Thus we have demonstrated that membrane properties can be modulated by simple structural changes at the amphiphile level. It was shown that by judicious incorporation of central, isomeric, disubstituted aromatic units as structural anchors into different bolaphiles, one can modulate the properties of the resulting vesicles.

Co-assembly of a Nafion-Mesoporous Zirconium Phosphate Composite Membrane for PEM Fuel Cells

Synthesis of mesoporous zirconium phosphate (MZP) by co-assembly of a tri-block copolymer, namely pluronic-F127, as a structure-directing agent, and a mixture of zirconium butoxide and phosphorous trichloride as inorganic precursors is reported. MZP with a specific surface area of 84 m(2) g(-1) average pore diameter of about 17 nm and pore volume of 0.35 cm(3) g(-1) has been prepared, and characterised by X-ray diffraction (XRD) and transmission electron microscopy. Nafion-MZP composite membrane is obtained by employing MZP as a surface-functionalised solid-super-acid-proton-conducting medium as well as all inorganic filler with high affinity to absorb water and fast proton-transport across the electrolyte membrane even under low relative humidity (RH) conditions. The composite membranes have been evaluated in H-2/O-2 polymer electrolyte fuel cells (PEFCs) at varying RH values between 18 and 100%; a peak power density of 355 mW cm(-2) at a load current density of 1,100 mA cm(-2) is achieved with the PEFC employing Nafion-MZP composite membrane while operating at optimum temperature (70 degrees C) under 18% RH and ambient pressure. On operating the PEFC employing Nafion-MZP membrane electrolyte with hydrogen and air feeds at ambient pressure and a RH value of 18%, a peak power density of 285 mW cm(-2) at the optimum temperature (60 degrees C) is achieved. In contrast, operating under identical conditions, a peak power density of only similar to 170 mW cm(-2) is achieved with the PEFC employing Nafion-1135 membrane electrolyte.

Fluorescent labelling of strychnine: A novel approach for recognition of strychnine binding sites on neuronal membrane

trychnine was coupled to fluorescein isothiocyanate to mark strychnine binding sites in spinal cord of rat. Specific binding of strychnine could be demonstrated in synaptosomal fraction. Addition of glycine to the strychninised membrane led to a decrease in fluorescence indicating same receptor loci.

Alamethicin and related membrane channel forming polypeptides

Alamethicin and several related microbial polypeptides, which contain a high proportion of agr-aminoisobutyric acid (Aib) residues, possess the ability to modify the permeability properties of phospholipid bilayer membranes. Alamethicin induces excitability phenomena in model membranes and has served as an excellent model for the study of voltage sensitive transmembrane channels. This review summarizes various aspects of the structural chemistry and membrane modifying properties of alamethicin and related Alb containing peptides. The presence of Aib residues in these sequences, constrains the polypeptides to 310 or agr-helical conformations. Functional membrane channels are formed by aggregation of cylindrical peptide helices, which span the lipid bilayer, forming a scaffolding for an aqueous column across the membrane. After consideration of the available data on the conductance characteristics of alamethicin channels, a working, hypothesis for a channel model is outlined. Channel aggregates in the lipid phase may be stabilized by intermolecular hydrogen bonding, involving a central glutamine residue and also by interactions between the macro-dipoles of proximate peptide helices. Fluctuations between different conductance states are rationalized by transitions between states of different aggregation and hence altered dimensions of the aqueous core or by changes in net dipole moment of the aggregate. Ion fluxes through the channel may also be affected by the electric field within the aqueous core.

The helical conformations of 14- and 16-residue fragments of suzukacillin, a membrane channel-forming polypeptide

The suzukacillin fragments, Boc-Ala-Aib-Aib-Gln-Aib-Leu-Aib-Gly-Leu-Aib-Pro-Val-Aib-Aib-OMe (14), Boc-Ala-Aib-Ala-Aib-Aib-Gln-Aib-Leu-Aib-Gly-Leu-Aib-Pro-Val-Aib-Aib-OMe (16G) and the completely apolar 16-residue peptide in which the glutamine residue has been replaced by alanine (16A) have been studied by 270 MHz 1H-HMR, in C2HCl3 and (C2H3)2SO solution. Intramolecularly hydrogen-bonded NH groups have been identified by temperature and solvent dependence of chemical shifts. Peptides 14 and 16A adopt folded 310 helical conformations stabilized by 11 and 13 hydrogen bonds, respectively. In peptide 16G there are 12 intramolecular hydrogen bonds, with the glycine NH being solvent-exposed, in contrast to 14 and 16A.

Changes in the Activities of two membrane-bound enzymes during solar eclipse on February 16, 1980

ON Saturday February 16, 1980 total solar eclipse Occurred for a period of 2-3 min in a belt of 135 km during the eclipse from 14'17 to 17'00 hrs across peninsular India. The city of Bangalore, being just outside this belt, had witnessed 92% eclipse for about 2. 1/2 min at the peak period of 15.44 hr at which time a temperature drop of 2' C and a considerable dimness of the light were experienced. In view of the interest in our laboratory on biochemical adaptation under conditions of environmental stress, we designed an experiment to study the possible changes in enzyme activities during the solar eclipse on February 16, 1980.

Helical conformations of three crystalline pentapeptide fragments of suzukacillin, a membrane channel forming polypeptide

The crystal structures of three pentapeptide fragments of suzukacillin-A have been determined. Boc-Aib-Pro-Val-Aib-Val-OMe (peptide 1–5) adopts a distorted helical conformation, stabilized by three intramolecular hydrogen bonds (two 5→1, one 4→1). Boc-Ala-Aib-Ala-Aib-Aib-OMe (peptide 6–10) and Boc-Leu-Aib-Pro-Val-Aib-OMe (peptide 16–20) adopt 310 helical structures stabilized by three and two 4→1 intramolecular hydrogen bonds, respectively. These structures provide substantial support for a largely helical conformation for the suzukacillin membrane channel.

The effects of slip velocity at a membrane surface on blood flow in the microcirculation

Closed-form solutions are presented for blood flow in the microcirculation by taking into account the influence of slip velocity at the membrane surface. In this study, the convective inertia force is neglected in comparison with that of blood viscosity on the basis of the smallness of the Reynolds number of the flow in microcirculation. The permeability property of the blood vessel is based on the well known Starling's hypothesis [11]. The effects of slip coefficient on the velocity and pressure fields are clearly depicted.

Mordenite-incorporated PVA-PSSA membranes as electrolytes for DMFCs

Composite membranes with mordenite (MOR) incorporated in poly vinyl alcohol (PVA)–polystyrene sulfonic acid (PSSA) blend tailored with varying degree of sulfonation are reported. Such a membrane comprises a dispersed phase of mordenite and a continuous phase of the polymer that help tuning the flow of methanol and water across it. The membranes on prolonged testing in a direct methanol fuel cell (DMFC) exhibit mitigated methanol cross-over from anode to the cathode. The membranes have been tested for their sorption behaviour, ion-exchange capacity, electrochemical selectivity and mechanical strength as also characterized by Fourier transform infrared spectroscopy and thermogravimetric analysis. Water release kinetics has been measured by magnetic resonance imaging (NMR imaging) and is found to be in agreement with the sorption data. Similarly, methanol release kinetics studied by volume-localized NMR spectroscopy (point resolved spectroscopy, PRESS) clearly demonstrates that the dispersion of mordenite in PVA–PSSA retards the methanol release kinetics considerably. A peak power-density of 74 mW/cm2 is achieved for the DMFC using a PVA–PSSA membrane electrolyte with 50% degree of sulfonation and 10 wt.% dispersed mordenite phase. A methanol cross-over current as low as 7.5 mA/cm2 with 2 M methanol feed at the DMFC anode is observed while using the optimized composite membrane as electrolyte in the DMFC, which is about 60% and 46% lower than Nafion-117 and PVA–PSSA membranes, respectively, when tested under identical conditions.

Aerodynamic characteristics of pretensioned elastic membrane rectangular sailwings

Presented in the paper are the details of a method for obtaining aerodynamic characteristics of pretensioned elastic membrane rectangular sailwings. This is a nonlinear problem governed by the membrane equation for the inflated sail and the lifting surface theory integral equation for aerodynamic loads on the sail. Assuming an admissible mode shape for the inflated elastic sail, an iterative procedure based on a doublet lattice method is employed to determine the inflated configuration as well as various aerodynamic characteristics. Application of the method is made to a typical nylon-cotton sailwing of AR = 6.0 and results are presented graphically to show the effect of various parameters. The results are found to tend to plane wing values when the pretensions are large in magnitude.

Adriamycin affects plasma membrane redox functions

Adriamycin (Doxorubicin) stimulates NADH oxidase activity in liver plasma membrane, but does not cause NADH oxidase activity to appear where it is not initially present, as in erythrocyte membrane. NADH dehydrogenase from rat liver and erythrocyte plasma membranes shows similar adriamycin effects with other electron acceptors. Both NADH ferricyanide reductase and vanadate-stimulated NADH oxidation are inhibited by adriamycin, as is a cyanide insensitive ascorbate oxidase activity, whereas NADH cytochrome c reductase is not affected. The effects may contribute to the growth inhibitory (control) and/or deleterious effects of adriamycin. It is clear that adriamycin effects on the plasma membrane dehydrogenase involve more than a simple catalysis of superoxide formation.