Concentration potentials of hydrophilic membranes containing ionogenic groups

The paper deals with studies of electrochemical properties of membranes from a copolymer of 2-hydroxyethyl methacrylate with ethylene dimethacrylate, modified by introducing weak acidic and/or weak basic groups. The acidic, basic and ampholytic membranes have been characterized by values of concentration potentials of KCl solution pairs with the concentration ratio 1:2, permselectivity and the course of membrane functions. Effects of the ionogenic group concentration, network density of the membranes and the hydrophilicity of the ionogenic group upon the electrochemical properties of membranes are discussed. Existence of a significant effect of the free diffusion on the value of concentration potentials is deduced especially from differences in slopes of the membrane functions.     

Permeability of membranes containing ionogenic groups

The present paper deals with the transport properties of membranes made of hydrophilic gels containing ionogenic groups. Introduction of ionogenic groups into a gel based on 2-hydroxyethyl methacrylate will affect the permeability of the investigated membranes for sodium chloride by an order or more. Dependences of the permeability on the content of ionogenic groups, three-dimensional network density, and pH were established. The permeability for NaCl was compared for that for bivalent salt (MgSO₄). It is shown, on the basis of independently determined distribution coefficients, that an increase in the permeability of ampholytic membranes in comparison with the neutral ones is primarily due to an increase in the diffusivity of the salt in the membranes with modified structure. It can also be concluded that an approximation of the free volume from the volume of the solvent in the membrane cannot be applied to the poly(2-hydroxyethyl methacrylate) gel.     

Interactions between poly(2-ethylacrylic acid) and lipid bilayer membranes: effects of cholesterol and grafted poly(ethylene glycol)

The exchange of the protonatable polymer, poly(2-ethylacrylic acid) (PEAA), has been studied with vesicle membranes containing cholesterol from 0 to 60 mol% or PEG2000-lipid (5 mol%). The release of an entrapped dye from 100 nm extruded liposomes was used as an assay for membrane perturbation by the polymer as a function of pH. The inclusion of cholesterol was found to reduce the pH at which the polymer caused release of the dye from the lipid vesicles, and the degree of polymer protonation (i.e., degree of hydrophobicity) correlated well with the increase in elastic expansion modulus of the vesicle bilayer. The results are discussed in terms of a balance between polymer solubility and membrane expansion. With respect to the PEG barrier, the presence of 5 mol% PEG2000, which represents full surface coverage, did not prevent PEAA from inducing contents release, demonstrating that highly hydrated polymeric layers are not effective barriers for other water soluble polymers, and may point to some association between the two polymers.     

Polarization characteristics of monopolar ionite membranes

An experimental setup (a membrane rotating disk electrode) is described. Combinations ionitepolyethylene applied in the production of membranes MK-40, MK-41, and MA-40 are used as compositions modeling commercial monopolar ionite membranes. The setup design allows one to separately measure the diffusion limitations on the let-in and let-out sides of membranes. The comparison of experimental polarization characteristics and theoretical dependences (plotted earlier) shows that a polarization characteristic is a net dependence for two processes of electromasstransfer. One process is associated with the diffusion limitations from the solution side. The other is attributed to the hydrolysis of fixed ionogenic groups of the membrane’s ionite and precedes the electrochemical stage of charge transfer across the membrane/electrolyte interface.     

Hydrophilic polymer membranes containing carboxylic groups—I. Acrylic acid—methyl methacrylate—glycidyl methacrylate copolymers

Copolymers of acrylic acid, methyl methacrylate and glycidyl methacrylate have been synthesized and converted into cross-linked hydrophilic membranes by successive treatments with heat, alkali solution and acidic solution. The copolymerization was carried out in solution using tetrahydrofuran and p-dioxane as solvents. The polymer was obtained as a clear viscous solution at yields of approximately 95%. The polymerization was stopped before gelation took place. This gelation resulted from the reaction of epoxy and carboxylic groups of the polymeric chain. The polymerization time ranged from 3.5 to 7 hr depending on the content of the glycidyl methacrylate in the feed. The monomer mixture consisted of 25–45 mol% of acrylic acid, 40–70 mol% of methyl methacrylate and 2.5–15 mol% of glycīdyl methacrylate. With increasing content of acrylic acid, the membranes became soft and elastic; with decreasing content, they became brittle and hydrophobic. The swelling of the cured polymeric film increased with increase in the acrylic acid content of the monomer mixture and decreased with increasing glycidyl methacrylate content. Dialysis runs were conducted with sodium chloride, urea and a series of ethylene glycols with molecular weights up to 600. The permeability coefficients through the membranes for the ethylene glycols were similar to those through a commercial cellulose membrane (Cuprophane). The permeability proportional to $\text{(permeant molecular wt)}{}^{\mathrm{<mtext>?</mtext><mtext>1</mtext><mtext>2</mtext>}}$. The membranes showed very low permeabilities to sodium chloride compared with those of commercial nonionic membranes. This appears to be due to the ionic exclusion mechanisms expected for ion exchange membranes.     

On the catalytic oxidation of ascorbic acid at self-doping polyaniline films

Ascorbic acid molecules in either acid or conjugate base forms have been oxidized on self-doping carboxylated polyaniline thin films. The kinetic model proposed by Bartlett et al. has been successfully applied to the catalytic reactions. Active sites in the polymer have been identified as the rings having quinoid character. The existence of significant electrostatic repulsions between ionogenic groups at the self-doping polymer and negatively charged ascorbate molecules has been established thanks to the analysis of the pH dependence of the Michaelis constant. It has been found that in contrast to inorganic conductors the regeneration of active sites in polyaniline-based materials is slower at higher potentials. Such a behavior can be satisfactorily correlated with the potential dependence of the polymer electronic conductivity.     

End-group cross-linked membranes based on highly sulfonated poly(arylene ether sulfone) with vinyl functionalized graphene oxide as a cross-linker and a filler for proton exchange membrane fuel cell application

High-performance end-group cross-linked sulfonated poly(arylene ether sulfone) (SPAES) membranes are developed using thiolate-terminated SPAES with very high degree of sulfonation (DS) such as 90 mol% (SK-SPAES90) and vinyl functionalized graphene oxide (VGO) as a cross-linker and a filler through the thiol-Michael addition reaction. Since free-standing membranes for fuel cell application could not be prepared using the water soluble and highly proton conductive SPAES with high DS of 90 mol%, cross-linked SPAES90 membranes are intentionally prepared. The cross-linked membranes are found to have good physicochemical properties with excellent proton conductivity that can be applied for the proton exchange membrane. In particular, the cross-linked SPAES90 membrane prepared using 1.0 wt% of VGO exhibits better dimensional stability than a SPAES70 membrane from the linear SPAES with DS of 70 mol% and the proton conductivities of this membrane are larger than those of Nafion 211 at 80 °C under different relative humidity conditions (40%-95%).     

Surface modification of phenolphthalein poly(ether sulfone) ultrafiltration membranes by blending with acrylonitrile-based copolymer containing ionic groups for imparting surface electrical properties

Asymmetric ultrafiltration membranes were fabricated from the blends of phenolphthalein polyethersulfone (PES-C) and acrylonitrile copolymers containing charged groups, poly(acrylonitrile-co-acrylamido methylpropane sulfonic acid) (PAN-co-AMPS). From the surface analysis by XPS and ATR-FTIR, it was found that the charged groups tend to accumulate onto the membrane surface. This result indicated that membrane surface modification for imparting surface electrical properties could be carried out by blending charged polymer. Furthermore, with the help of a relatively novel method to measure membrane conduction, the true zeta potentials calculated on the basis of the streaming potential measurements were used to reflect the charge state of membrane surface. In addition, it was noteworthy that, from the profiles of zeta potential versus pH curves and the magnitude of zeta potentials, the determination of zeta potential was dependent not only on the electrical properties of membrane surface but also on its hydrophilicity. At last, based on a relatively elaborate study on the electrostatic interaction between the membrane surface and protein, it was found that these charged membranes could meet different demands of membrane applications, such as resisting protein fouling or protein separation, through adjusting solution pH value.     

Influence of the nature of membrane ionogenic groups on water dissociation and electrolyte ion transport: A rotating membrane disk study

Polarization properties of electromembrane systems (EMS) consisting of a heterogeneous membrane, either the MK-41 phosphonic acid membrane or the MK-40 sulfonic acid membrane, and dilute sodium chloride solutions are investigated with the rotating membrane disk method. For the MK-41/0.01 M NaCl and MK-41/0.001 M NaCl EMS, effective ion transport numbers and partial current-voltage curves (CVC) are measured for sodium and hydrogen ions, and limiting-current densities and the diffusion-layer thickness are calculated as functions of the rotation rate of the membrane disk. With the theory of the overlimiting state of EMS, internal parameters of the systems under investigation—the diffusion-layer thickness, the space-charge distribution, and electric-field strengths in the diffusion layer and in the membrane—are calculated from experimentally obtained CVC and the dependence of effective transport numbers on current density. The catalytic influence of ionogenic groups on the dissociation rate of water is analyzed quantitatively. Partial CVC for H⁺ ions are calculated for the space-charge region in MK-40 and MK-41 membranes. Analogous CVC for bipolar membranes containing sulfonic acid and phosphonic acid groups are compared. The dissociation mechanism of water is the same in all EMS and is independent of the membrane type and the nature of the functional groups.     

Effect of the chemical nature of the ionogenic groups of ion-exchange membranes on the size of the electroconvective instability region in high-current modes

The size of the electroconvective instability region on the membrane-solution boundary at currents exceeding the limiting diffusion current was measured by laser interferometry. The influence of the chemical nature of the ionogenic groups of ion-exchange membranes on the development of electroconvective instability was studied. The thickness of the electroconvection region decreased as the catalytic activity of the ionogenic groups of commercial and pilot membrane samples with respect to the heterolytic water dissociation increased. The maximum size of the electroconvective instability region and the minimum currents at which it was recorded for the anion-exchange membranes under study were determined for the highly basic modified anion-exchange membrane MA-41M with an almost completely suppressed water dissociation function. A correlation was found between the size of the convective instability region and the characteristic points on the current-voltage curves.     

Determination of acid-base dissociation constants of amino- and guanidinopurine nucleotide analogs and related compounds by capillary zone electrophoresis

CZE has been applied for determination of acid-base dissociation constants (pKa) of ionogenic groups of newly synthesized amino- and (amino)guanidinopurine nucleotide analogs, such as acyclic nucleoside phosphonate, acyclic nucleoside phosphonate diesters and other related compounds. These compounds bear characteristic pharmacophores contained in various important biologically active substances, such as cytostatics and antivirals. The pKa values of ionogenic groups of the above compounds were determined by nonlinear regression analysis of the experimentally measured pH dependence of their effective electrophoretic mobilities. The effective mobilities were measured by CZE performed in series of BGEs in a broad pH range (3.50-11.25), at constant ionic strength (25 mM) and temperature (25 degrees C). pKa values were determined for the protonated guanidinyl group in (amino)guanidino 9-alkylpurines and in (amino)guanidinopurine nucleotide analogs, such as acyclic nucleoside phosphonates and acyclic nucleoside phosphonate diesters, for phosphonic acid to the second dissociation degree (-2) in acyclic nucleoside phosphonates of amino and (amino)guanidino 9-alkylpurines, and for protonated nitrogen in position 1 (N1) of purine moiety in acyclic nucleoside phosphonates of amino 9-alkylpurines. Thermodynamic pKa of protonated guanidinyl group was estimated to be in the range of 7.75-10.32, pKa of phosphonic acid to the second dissociation degree achieved values of 6.64-7.46, and pKa of protonated nitrogen in position 1 of purine was in the range of 4.13-4.89, depending on the structure of the analyzed compounds.     

Electrokinetics of a poly(N-isopropylacrylamid-co-carboxyacrylamid) soft thin film: evidence of diffuse segment distribution in the swollen state

Streaming current measurements were performed on poly(N-isopropylacrylamid-co-carboxyacrylamid) (PNiPAAM-co-carboxyAAM) soft thin films over a broad range of pH and salt concentration (pH 2.5-10, 0.1-10 mM KCl) at a constant temperature of 22 °C. The films are negatively charged because of the ionization of the carboxylic acid groups in the repeat unit of the copolymer. For a given salt concentration, the absolute value of the streaming current exhibits an unconventional, nonmonotonous dependence on pH with the presence of a maximum at pH ～6.4. This maximum is most pronounced at low electrolyte concentration and gradually disappears with increasing salinity. Complementary ellipsometry data further reveal that the average film thickness increases by a factor of ～2.2 with increasing pH over the whole range of salt concentration examined. The larger the solution salt concentration, the lower the pH value where expansion of the hydrogel layer starts to take place. The dependence of film thickness on pH and electrolyte concentration remarkably follows that obtained for surface conductivity. The streaming current and surface conductivity results could be consistently interpreted on a quantitative basis using the theory we previously derived for the electrokinetics of charged diffuse (heterogeneous) soft thin films complemented here by the derivation of a general expression for the surface conductivity of such systems. In particular, the maximum in streaming current versus pH is unambiguously attributed to the presence of an interphasial gradient in polymer segment density following the heterogeneous expansion of the chains within the film upon swelling with increasing pH. A quantitative inspection of the data further suggests that pK values of ionogenic groups in the film as derived from the streaming current and surface conductivity data differ by ～0.9 pH unit. Such a difference is attributed to the impact of position-dependent hydrophobicity across the film on the degree of ionization of carboxylic sites.     

Sorption and transport behavior of gasoline components in polyethylene glycol membranes

Desulphurization mechanism of polyethylene glycol (PEG) membranes has been investigated by the study of solubility and diffusion behavior of typical gasoline components through PEG membranes with various crosslinking degrees. The sorption, diffusion and permeation coefficients were calculated by the systematic studies of dynamic sorption curves of gasoline components such as thiophene, n-heptane, cyclohexane, cyclohexene and toluene in PEG membranes. Furthermore, the temperature dependence of diffusion and solubility coefficients and the influence of crosslinking degree on sorption and diffusion behaviors were conducted to elucidate the mass-transfer mechanism. According to the discussions on dynamic sorption curves, transport mode, activation energy and thermodynamic parameters, thiophene species were the preferential permeation components. Crosslinking is an effective modification way to improve the overall performance of PEG membranes applied in gasoline desulphurization. The pervaporation (PV) and gas chromatography (GC) experiments results corresponded to the conclusions. All these investigations will provide helpful suggestions for the newly emerged membrane desulphurization technology and complex organic mixture separation by pervaporation.     

Self-organization of sulfopolystyrene ionomers in solutions: Dependence on the polarity of the solution and the content of ionogenic groups in chains

The self-organization of ionomers of sulfonated polystyrene containing different amounts of SO₃Na ionogenic groups (0.5, 1.35, and 2.6 mol %) in three solvents (benzene, toluene, and THF) is studied via the methods of neutron scattering. It is shown that, in toluene, ionogenic groups form “effective” chains of up to 10–20 macromolecules owing to aggregation. In benzene, chains of both the PS precursor and ionomers are surrounded by volume solvate shells in the form of ∼4-nm-dia tubes that hamper interaction between ionomers via ionogenic groups. The tendency of ionomer chains toward aggregation in benzene is enhanced as the content of polar groups in chains is increased to 2.6 mol %. The diameter of solvate shells around chains decreases to ∼1 nm, and chains associate to form denser structures. In this case, the degree of integration of macromolecules turns out to be smaller than that in toluene. In THF, the processes of solvation and structuring of PS precursor chains are well defined and compete with tendencies toward association through ionogenic groups in solutions of ionomers. The formation of developed supramolecular structures in THF is hindered by the shielding of the potentials of interaction between ion pairs because of a high dielectric constant of the solvent.     

A method for studying swelling kinetics based on measurement of electrical conductivity

A novel method was applied to the study of swelling kinetics of pH-responsive hydrogels. This technique is based on the pH-dependent electrical conductivity of these materials, which is measured by coating planar interdigitated electrode arrays with thin hydrogel membranes. To demonstrate the utility of the method, the swelling kinetics of a well-characterized pH-responsive hydrogel were studied. Cross–linked copolymers of 2-hydroxyethyl methacrylate (HEMA) with up to 20 mol% dimethylaminoethyl methacrylate (DMA) were studied as a function of copolymer composition in phosphate or triethanolamine buffer at buffer concentrations from 1 to 100 mM. The experiments consisted of measuring the change in electrical resistance of a hydrogel-coated electrode array following a small pH change in the external buffer medium. The characteristic response time to reach a new equilibrium following a pH change was proportional to the concentration of DMA within the polymer and was inversely proportional to the buffer concentration. The characteristic response times for devices tested in phosphate buffer were a function of the magnitude of the pH step, increasing from 2.6 to 5.6 min as the step size increased from 0.2 to 0.57 pH units. However, the response times for devices tested in triethanolamine were independent of step size. The observed dependences upon the values of the dissociation constant (pK_a) of the buffering ion, the apparent pK_a of DMA, and the pH of the external bath agreed with buffer-mediated diffusion–reaction theory, and as such this conductimetric method represents a powerful tool for the study of swelling kinetics of responsive hydrogels.     

Development of a Poly(vinyl chloride)-based Nitrate Ion-selective Electrode

The authors developed a nitrate ion-selective electrode(ISE) based on poly(vinyl chloride)(PVC) membrane with methyltrioctylammonium nitrate as a carrier and 1-decanol as a plasticizer. The performance of the nitrate-sensitive membranes was optimized by tuning the composition of components. The electrode exhibits a linear response with a Nernstian slope of (52±1.0) mV per decade for the nitrate ion concentration ranging from 5.8×10^-5 mol/L to 1.0 mol/L. The electrode can be used to detect a low concentration of nitrate ions down to 3×10^-5 mol/L in a pH range of 2.1-11.5 without any compensation. The advantage of the electrode includes simple preparation, short response time and good repeatability. The detection performance of the novel electrode on nitrate ions has been tested for water samples.     

苯乙烯/马来酸酐和苯乙烯/甲基丙烯酸二甲氨基乙酯二元体系在聚四氟乙烯多孔膜上的γ辐射接枝

在氮气的氛围下用γ辐照的方法在聚四氟乙烯多孔膜上接枝苯乙烯 马来酸酐、苯乙烯 甲基丙烯酸二甲氨基乙酯二元单体 .并且研究了剂量、剂量率、溶液中单体的浓度和二元单体的摩尔比等条件对接枝率的影响 .探讨了两种单体的竞聚率对接枝率、接枝膜的组成及性能的影响 .结果表明 ,苯乙烯 马来酸酐二元体系对接枝率有协同效应 ,苯乙烯 甲基丙烯酸二甲氨基乙脂二元体系对接枝率表现为加合效应 .制备的二元接枝的聚四氟乙烯多孔膜可以进一步磺化来制备用于质子交换膜燃料电池的质子交换膜 .     

Highly sensitive and selective solid-contact calcium sensor based on Schiff base of benzil with 3-aminosalycilic acid covalently attached to polyacrylic acid amide for health care

Solid-state potentiometric calcium sensors based on newly synthesized Schiff’s base of 3-aminosalycilic acid with benzil [2-hydroxy-3-(2-oxo-1,2-diphenylethylidene)amino) benzoic acid] ionophore I and with isatin [2-hydroxy-3-(2-oxoindolin-3-ylidene amino)benzoic acid] ionophore II ionophores and their covalently attached to polyacrylamide ionophores III and IV, respectively, were developed. The all-solid-state sensors were constructed by the application of a thin film of polymeric membrane cocktail onto gold electrodes that were pre-coated with the conducting polymer poly (3,4-ethylenedioxy-thiophen) as an ion and electron transducer. More than 40 sensors with membranes containing plasticized PVC or poly(butyl methacrylate-co-dodecyl methacrylate as a plasticizer-free membrane matrix were investigated. The constructed sensors contained various amounts of the different ionophores with and without anionic lipophilic additive. The sensor containing 10% of ionophore III and 3% tetra (p-chlorophenyl) borate in acrylate copolymer exhibited a stable potentiometric response over a wide pH range of 4–9. It possessed a linear concentration range of 6 10^?10 to 1 10^?2 mol L^?1 with a Nernstian slope of 28.5 mV/decade and a limit of detection (LOD) of 2 10^?10 mol L^?1. It exhibited a good selectivity for calcium to other cations. The selectivity coefficients towards different mono-, di- and trivalent cations were determined with the fixed interference method (FIM) and separate solution method (SSM). The sensor’s life time is more than 3 months, without significant deterioration in the slope. The proposed sensors were utilized for the determination of calcium concentration in serum. The results were compared with those obtained from routine clinical laboratory electrolyte analyser. The results reveal that the all-solid-state calcium sensor is promising for the point of care testing.     

Novel hydrogel membrane based on copoly(hydroxyethyl methacrylate/p-vinylbenzyl-poly(ethylene oxide)) for biomedical applications: properties and drug release characteristics

The aim of this study was to synthesize and characterize a novel biocompatible polymeric membrane system and demonstrate its potential use in various biomedical applications. Synthetic hydrogels based on poly(hydroxyethyl methacrylate), poly(HEMA), have been widely studied and used in biomedical fields. A novel copolymer hydrogel was prepared in the membrane form using 2-hydroxyethyl methacrylate monomer (HEMA) and a macromonomer p-vinylbenzyl-poly(ethylene oxide) (V-PEO) via photoinitiated polymerization. A series of poly(HEMA/V-PEO) copolymer membranes with different compositions was prepared. The membranes were characterized using infrared, thermal and SEM analysis. The thermal stabilities of the copolymer membranes were found to be lowered by an increase in the ratio of macromonomer (V-PEO) in the membrane structure. Because of the incorporation of PEO segments, the copolymers exhibited significantly higher hydrophilic surface properties than pure poly(HEMA), as demonstrated by contact angle measurements. Equilibrium swelling studies were conducted to investigate the swelling behavior of the membranes. The equilibrium water uptake was reached in about 4 h. Moreover, the blood protein adsorption and platelet adhesion were significantly reduced on the surface of the PEO containing copolymer membranes compared to control pure poly(HEMA). Drug release experiments were performed in a continuous release system using model drug (vancomycin) loaded copoly(HEMA/V-PEO) membranes. A specific poly(HEMA/V-PEO) membrane formulation possessing the highest PEO content (with a HEMA:V-PEO (mmol:mmol) feed ratio of 112:1 and loaded with 40 mg antibiotic/g polymer) released about 81% of the total loaded drug in 24 h at pH 7.4. This membrane composition provided the best results and can be considered as a potential candidate for a transdermal antibiotic carrier and various biomedical and biotechnological applications.     

Hydrogel Membrane Improves Batch‐to‐Batch Reproducibility of an Enzymatic Glucose Biosensor

A permselective membrane is a critical component that defines the linear detection limits, the sensitivity, and thus the ultimate efficacy of an enzymatic biosensor. Although membranes like epoxy‐polyurethane (epoxy‐PU) and Nafion are widely used and provide the desired glucose detection limits of 2 to 30 mM, both the within batch and batch‐to‐batch variability of sensors that use these materials is a concern. The hypothesis for this study was that a crosslinked hydrogel would have a sufficiently uniform porosity and hydrophilicity to address the variability in sensor sensitivity. The hydrogel was prepared by crosslinking di‐hydroxyethyl methacrylate, hydroxyethyl methacrylate and N‐vinyl pyrrolidone with 2.5 mol% ethylene glycol dimethacrylate using water soluble initiators – ammonium persulfate and sodium metabisulfite under a nitrogen atmosphere. The hydrogel was applied to the sensor by dip coating during polymerisation. Electrochemical measurements revealed that the response characteristics of sensors coated with this membrane are highly consistent. Scanning electrochemical microscopy (SECM) was used to spatially resolve glucose diffusion through the membrane by measuring the consequent H₂O₂ release and compared with an epoxy‐PU membrane. Hydrogen peroxide measurements using SECM revealed that the epoxy‐PU membranes had uneven lateral diffusion profiles compared to the uniform profile of the hydrogel membranes. The uneven diffusion profiles of epoxy‐PU membranes are attributed to a fabrication method that results in uneven membrane properties, while the uniform diffusion profiles of the hydrogel membranes are primarily dictated by their uniform pore size.