Effect of carrier concentration on the facilitated oxygen transport in a polymer membrane

Facilitated transport of oxygen in a solid Polymer membrane containing cobaltporphyrin (CoP) which carries oxygen specifically and reversibly, leads to permselectivity of oxygen against nitrogen in the membrane. The increase in concentration of the CoP carrier is expected to enhance the oxygen transport. The membranes of poly(octylmethacrylate-co-vinylimidazole) containing 0.8 ～ 10 wt% CoP were prepared, and the effects of the CoP-concentration on the transport and the diffusion constants of oxygen are studied. Although the induction period before the steady state of oxygen permeation was prolonged with the CoP concentration in the polymer membrane, the glass transition temperature (T_g) of the membrane was increased and the diffusion constants of oxygen were decreased with the CoP concentration to yield unexpected reduction of the oxygen permeation in the highly CoP loaded membrane.     

Modelling of solute transport across a temperature-sensitive polymer membrane

An important target of many controlled release systems is to properly modify the drug release behaviour in response to some external stimuli like temperature or pH changes. The copolymer gels made up by poly(N,N-dimethylaminoethyl methacrylate (DMAEMA)-co-acrylamide (AAm)), being thermosensitive, are suitable systems for the thermocontrol of the solute release. Modifying the ratio DMAEMA/AAm, one may select the copolymer systems showing desired swelling properties. In order to better design such systems and in order to understand better the solute transport through the copolymer membrane, a mathematical model has been developed. The model employs suitable flux equations for the water uptake or release and for the solute (hydrocortisone) diffusion. With the condition of knowing the copolymer swelling kinetics, the model is able to describe in a reasonably good manner the solute transport across a DMAEMA-AAm membrane undergoing step temperature changes.     

On the streaming potential across a cation-exchange membrane

Electrical potentials developed during streaming of methanol, water and their mixtures through a Zeokarb 225 (Al⁺⁺⁺ form) membrane have been investigated. Build-up of streaming potential with time has been examined and discussed. Results indicate that dependence of streaming potential on applied pressure difference is non-linear and shows sign reversals. An attempt has been made to explain the results in terms of changes in the structure of electrical double layer at the membrane-permeant interface under the action of streaming pressure.With 4 figures     

Bi-ionic membrane potential across a liquid anion-exchange membrane containing triphenyltin chloride

Potentiometric selectivities of a liquid anion-exchange membrane containing triphenyltin chloride (TPTCl) to several inorganic anions were evaluated via measurements of the membrane potential of a bi-ionic system, also called bi-ionic membrane potential. Addition of TPTCl to the liquid anion-exchange membrane, based on the quaternary ammonium salt, gave rise to a quite different selectivity pattern from the so-called Hofmeister anion series observed for the liquid anion-exchange membrane. An additivity rule of the bi-ionic membrane potential was observed to hold for the liquid anion-exchange membrane containing TPTCl. Thus, the following multiple chain rule was derived for selectivity coefficients; k_1,n^pot = k_1,2^pot · k_2,3^pot … k_i,(i+1)^pot … k_n−1,n^pot where k_i,i+1^pot is the selectivity coefficient of the membrane for the (i + 1)th ion over the ith ion.     

Excess proton solvation and delocalization in a hydrophilic pocket of the proton conducting polymer membrane nafion

Solvation properties of the hydrated excess proton are studied in a hydrophilic pocket of Nafion 117 through a series of molecular dynamics simulations. The multistate empirical valence bond (MS-EVB) methodology, which enables the delocalization of the excess proton through the Grotthuss hopping mechanism, was employed for one of the excess protons in the simulation cell. Simulations were performed such that "classical" nondissociable hydronium cations and a single excess proton treated with the MS-EVB methodology were at a concentration ratio of 39:1. Two degrees of hydration of the Nafion polymer electrolyte membrane were simulated, each displaying the same marked difference between the solvation structures of the classical versus MS-EVB treated (Grotthuss shuttling) excess proton species. These differences are attributed to the solvent dynamics needed to transfer the cation between the solvent separated and contact pair positions about the sulfonic acid counterion. The results demonstrate that it is generally impossible to describe the low pH conditions in the hydrophilic domains of Nafion without the explicit treatment of Grotthuss delocalization in the underlying molecular dynamics model for the excess protons.     

Study on the oscillating phenomena of electrical potential across a liquid membrane

The electrical oscillations across a liquid membrane in water/oil/water system was studied with octanol as oil phase by introducing two opposite charged surfactants in oil and aqueous phase, respectively. The sustained and rhythmic oscillation was observed. To a certain extent, the features of the oscillation (e.g. induction time, frequency, life time and orientation of the pulse pikes) strongly depend on the property of surfactant, dissolved in octanol. The mechanism may be explained by the formation and destruction of dual-ion surfactant membrane accompanying with emulsification at the interface and considering the coupling effect of diffusion and associated reaction in the vicinity of the interface.     

Anti-biofouling properties of an amphoteric polymer brush constructed on a glass substrate

An amphoteric copolymer brush of methacrylic acid (MA) and 2-(dimethylamino)ethyl methacrylate (DMAEMA) was prepared by reversible addition-fragmentation chain-transfer (RAFT) polymerization using both a free chain transfer agent (n-butylsulfanylthiocarbonylsulfanyl-2-methyl propionic acid) and a radical initiator (4,4'-azobis(4-cyanopentanoic acid)) covalently fixed to a glass substrate. An aqueous solution of the copolymer, Poly(MA-r-DMAEMA), which was simultaneously obtained in liquid phase, had a sufficiently small polydispersity in its molecular weight. The copolymer brush showed effective suppression of non-specific adsorption of bovine serum albumin and egg white lysozyme to the brush. In contrast, both negatively charged PolyMA and positively charged PolyDMAEMA brushes significantly adsorbed the proteins irrespective of their net charges. Upon ion beam irradiation, furthermore, a hollow space with a designed shape could be made on the glass substrate, and both HEK293 and HepG2 cells non-specifically adhered to the space, forming aggregates, while no adhesion to the non-treated area on the brush was observed. These results suggest that the amphoteric polymer brushes will be useful materials for biomedical applications.     

Studies on membrane concentration potentials across heavy metal soap discs

The electrostatic effect of specifically adsorbed electroinactive ions upon electrode processes involving adsorbed reactants with a time of adsorption greater than the characteristic time of surface-diffusion jumps is considered. The validity of the most general form of the Frumkin correction term for double-layer effects, with ψ₁ equal to the local potential ₃ at the position occupied by the reactant in the transition state, is first examined on the basis of current molecular theories of electrode kinetics. Subsequently, approximate expressions of ₃ are derived for the case in which adsorbed reactant and adsorbed supporting ion are charged both of equal and of opposite sign. In both cases the logarithm Φ of the rate constant for the electrode reaction at constant applied potential, as corrected for diffuse-layer effects only, is expected to vary linearly with the charge density q_i due to the adsorbed supporting ion. |ΔΦ/Δq_i| is, however, much greater in the case of electrostatic attraction between reactant and adsorbed supporting ion than in the case of electrostatic repulsion. The influence of reactant adsorption with partial charge transfer upon the magnitude of ΔΦ/Δq_i is considered.     

Photoexcitable polymer membranes. Photoinduced membrane potential across poly(vinyl chloride) membrane doped with a photosensitive crown ether having lipophilic side chain

Photoirradiation induced potential changes of 10–20 mV across the poly(vinyl chloride) membranes doped with a photosensitive lipophilic crown ether, p-[3,4-(1,4,7,10,13-pentaoxatridecane-1,13-diyl)phenylazo]hexadecyloxybenzene was studied. The photoresponse of the membrane was highly improved, presumably due to the lipophilic nature of the crown ether. The photoresponse was explained in terms of the charge density change on the membrane surface. The electric double layer theory was applied to estimate the values of the photoinduced change of the charge density.     

Effects of radially dependent parameters on proton transport in polymer electrolyte membrane nanopores

A three-dimensional continuum model is explored to investigate the effects of radially dependent system parameters, such as relative permittivity and viscosity, on the transport of proton and water in nanoscale cylindrical pores of a fully hydrated polymer electrolyte membrane (PEM). The model employs Poisson, Nernst-Planck, and Stokes equations. Based on evidence from the literature for the presence of a stagnant water layer near the pore surface, we assume that a no-slip surface is located inside the pore, a few Angstroms from the pore wall. To solve the system numerically, the steady-state solution for the transport of protons and water is considered to be a perturbation around the equilibrium solution. Our results indicate that a radial variation of relative permittivity has the greatest influence on pore conductivity, reducing it by about 50% when compared to that of constant permittivity. On the other hand, viscosity plays the dominant role when the effective water drag within such pores is considered. We conclude that a continuum approach, including constant viscosity, is applicable in nanoscale models provided that the location of the no-slip surface is properly specified and the radial variation of the relative permittivity is taken into consideration.     

Enhanced proton conductivity of polymer electrolyte membrane doped with titanate nanotubes

Nafion-titanate nanotubes composite membranes were prepared through a casting process. With the addition of 5 wt.%, the nanotubes were homogenously distributed in Nafion solution. The formed composite membrane showed a comparable mechanical strength to Nafion membrane. The proton conductivity of the composite membrane without external humidification is higher than that of the Nafion membrane, reaching 0.034 Scm^?1 and 0.01 Scm^?1 at 100 °C and 120 °C, respectively. The improved proton conductivity was attributed to the great water retention ability of the doped nanotubes.     

Formation and characterization of asymmetric nanofiltration membrane: Effect of shear rate and polymer concentration

In this study, we report the effects of shear rates and polymer concentrations in the formation of asymmetric nanofiltration membrane using a simple dry/wet phase inversion technique. Employing the combination of irreversible thermodynamic model, solution-diffusion model (Spiegler–Kedem equation), steric-hindrance pore (SHP) model and Teorell–Meyers (TMS) model, the transport mechanisms and membrane structural properties were determined and have been characterized for different cases of those formation parameters. The experimental and modeling showed very promising results in terms of membrane performance with interesting structural details. The optimum shear rate (critical shear rate) was found to be at about 203.20 s⁻¹ and the best polymer concentration toward the formation of high performance nanofiltration membrane is in the range of 19.60–23.10%. The modeling results suggested that the pore radius of the membranes produced lies within the range of pore radius of 29 commercial available membranes. This study also proposed that the electrolytes transport through nanofiltration membrane was dominated by a convection factor which accounted approximately 30% more than a diffusion factor. This study also indicated that shear rate and polymer concentration were found to affect the membrane performance and structural properties by providing, to a certain extent, an oriented membrane skin layer which in turn exhibiting an improvement in membrane separation ability.     

Effect of a film layer on mono-divalent bi-ionic membrane potential

The bi-ionic potential generated across a standard cation exchange membrane was investigated in a mono-divalent bi-ionic system. Applying Henderson's theory to the film layer, the Nernst—Planck equation was solved in the film layer as well as in the membrane. The observed potentials were compared with the theoretically predicted values from parameters such as bulk concentrations, diffusion coefficients in the membrane and in solution, exchange capacity, corrected molar selectivity coefficient, and film layer thickness. The calculated potentials were not always in agreement with the experimental values, but reproduced properly the trend of potential change with concentration and stirring rate. The constituent potentials, i.e. the diffusion potentials in the film layer and in the membrane and the interfacial potentials, are also discussed. In the sodium—calcium bi-ionic system, the primary contribution to the total membrane potential was not the diffusion potential in the film layers and in the membrane, but the sum of two interfacial potentials. p]In the case of membrane-diffusion control, the bi-ionic potential was confirmed to follow the equation of Helfferich.     

Effect of the langmuir-type ion adsorption on the membrane potential of a non-charged membrane

Membrane potential is determined by the combination of the properties of ions and of the membrane. There is, therefore, a possibility that the properties of ions can be reflected on the membrane potential more effectively by artificially modifying the membrane properties. In this paper, the membrane is assumed to have no charge but to adsorb cations or anions selectively, and the effect of Langmuir-type adsorption of ions on the membrane potential is investigated theoretically. The variation of the amount of adsorbed ions affects not only the surface potential but also the diffusion potential within the membrane. The membrane potential shows a minimum or a maximum with the variation of the ion concentration in the bulk solution. This phenomenon results from the variation of the amount of ions adsorbed onto the membrane surfaces. Therefore, information on both the adsorption coefficient of a given ion and the amount of saturation of absorption of the ion is obtained from an analysis of the membrane potential. The theory is applied to the analysis of the affinity membrane potential, which can be used for the determination of blood type, and it is shown that the theory is in good agreement with experimental data.     

Intensification of proton conductivity through polymer electrolytic membrane using novel electrode pattern

The performance of a polymer electrolyte membrane fuel cell is contingent on the focal property of the protonic conductivity to accelerate the electrochemical reaction based on the membrane activity or on the uniform and even distribution of the reactants. For the even distribution, novel Flow Fields (FF) of the electrode pattern are obligatory to maintain the distribution for a long period for the conversion of protons from the anode reactant. In this study, a novel X Flow Field (XFF) electrode pattern is developed and compared with the conventional serpentine Flow Field (SFF) electrode pattern numerically and experimentally. The performance of the cell through the XFF electrode pattern has shown an improvement of 14.89% numerically and 14.61% experimentally as it distributes the reactants evenly to accelerate the electrochemical reaction, and induce a lower pressure drop and lower water saturation. The effect of pressure and Mass Flow Rate (MFR) of the reactants on the cell performance is discussed and it is found that the increment in Power Density (PD) of the cell is proportional to the increment of the MFR and the pressure because of the even distribution of the reactants, better membrane protonic conductivity, enhancement of the electrode kinetics and improvement in the mass transfer.     

Molecular dynamics simulations of heptyl phosphonic acid: a potential polymer component for fuel cell polymer membrane

Atomistic molecular dynamics simulations have been performed on heptyl phosphonic acid (HPA) to understand the dynamic hydrogen bonding network in the liquid phase. HPA is a phosphonic-acid functionalized alkane (heptane) and a model compound for one of the promising polymers for high temperature (>100 degrees C) fuel cell polymer electrolyte membranes. For the simulation, a force field for this molecule has been generated with the help of quantum chemical calculations and optimized by simplex algorithm. The force field has been validated against experimentally measured properties, for example, density and self-diffusion constant. From molecular dynamics simulations conducted at different temperatures, we have confirmed the hypothesis of dynamic hydrogen bond network formation in this material.     

Effect of salt concentration on the nanostructure of weak polyacid brush in the amphiphilic polymer monolayer at the air/water interface

The effect of salt concentration on the nanostructure of a spread monolayer of ionic amphiphilic diblock copolymer, (diethylsilacyclobutane)m-b-(methacrylic acid)n, at the air-water interface was directly investigated by in situ X-ray reflectivity and neutron reflectivity techniques. Previously, we had found that a poly(methacrylic acid) (PMAA) hydrophilic layer under the water was not in the form of a simple polyelectrolyte brush but consisted of a dense carpet upper layer and a diffuse brush lower layer when the hydrophilic chain was long enough. Here we observed this double layer formation in the monolayer in aqueous NaCl solution at a constant surface pressure. The effect of salt added to the subphase differed with the salt concentrations, that is, below or above 0.1 M. In the presence of NaCl up to 0.1 M, both the hydrophobic layer and brush layer thicknesses decreased. On the other hand, both of them increased in the presence of NaCl above 0.1 M. Also, the carpet layer thickness was almost constant independent of the salt concentration. In addition, the brush top roughness showed a maximum in the presence of 0.1 M NaCl. The increase of the charge number on the PMAA chain and the screening effect of the Coulomb interaction by added salt ions were considered to be responsible for these phenomena.     

Novel phosphonated polymer without anhydride formation for proton exchange membrane fuel cells

Proton exchange membrane fuel cells(PEMFCs)are regarded as one of the most promising clean energy technology because of their high energy density,silent emission-free operation,and wide applications[1].Recently,anion exchange membrane fuel cells(AEMFCs)has emerged as an alternative to PEMFCs.