Micro-Raman investigations of PVDF-based proton-conducting membranes

Proton-conducting membranes of poly(vinylidene fluoride), PVDF, grafted with styrene and thereafter sulfonated, were investigated by Raman spectroscopy. The depth and surface distribution of polystyrene grafts and crosslinker, as well as the sulfonation efficiency, were determined by using confocal micro-Raman spectroscopy. Highly grafted samples show homogeneous distribution of grafted material and homogeneous sulfonation. Depth profiles reveal uneven graft distribution for samples with low and intermediate degrees of grafting. In crosslinked samples, the crosslinker concentration in the interior of the film is found to be roughly 50% of the surface concentration. In contrast to what has previously been reported, the sulfonation efficiency is poor at low graft levels and is further inhibited by the presence of divinyl benzene, DVB, as crosslinker. At degrees of grafting above ∼ 60%, the crosslinker does not affect the sulfonation efficiency and a level of 70–90% sulfonation is reached. The matrix polymer structure is found to be largely retained after irradiation, grafting, and sulfonation. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3317–3327, 1999     

Effect of lithium addition on the performance of proton-conducting catalysts for oxidative coupling of methane under microwave irradiation

The oxidative coupling of methane over lithium modified proton-conducting catalysts irradiated by microwaves has been studied. Compared with protonconducting catalysts, lithium addition to proton-conducting catalysts resulted in changes in product species and product selectivities, favoring the production of C₂ compounds.     

Wide-range regulation of polyaniline conduction by interphase doping of a polyaniline film

The not-sufficient-enough conductance of semioxidized protonated polyaniline (PANI) is usually attributed to the presence of ordered quasi-metallic domains surrounded by a poorly conducting amorphous phase. The paper presents experimental results testifying to the existence, in semioxidized PANI, of multilevel redox heterogeneity that crucially effects the conductance magnitude in view of specific topology at which higher-oxidized (conducting) domains are surrounded by less oxidized (poorly conducting) domains and because the PANI conduction is extremely sensitive to the oxidation degree. It is shown experimentally that the interphase doping with metals and degenerate semiconductors of a semioxidized salt of PANI and poly(2-acrylamide-2-methyl-1-propanesulfonic acid) (PAMPSA) with a 1: 2 ratio between PANI and PAMPSA raises the PANI-PAMPSA conductivity by 3–8 orders of magnitude due to the formation near the interface of thin layers whose conductance depends on the work function of the material in contact with PANI-PAMPSA and in extreme cases substantially exceeds the conductance of gold and copper at room temperature.     

Microstructured proton-conducting membranes by synchrotron-radiation-induced grafting

Selective exposures of poly(ethylene-alt-tetrafluoroethylene) (ETFE) films with hard X-rays through high aspect ratio Ni-masks were performed at the LIGA3 beamline of the “Angström Quelle Karlsruhe” (ANKA) to create patterns of radicals used as initiators for the grafting of styrene into the bulk of the ETFE films. Grafted films were then sulfonated to obtain proton-conducting membranes. The structure definition, as investigated by scanning electron microscopy (SEM), showed a perfect discrimination between exposed and shaded areas through all the film thickness. Structuring results in a more homogeneous appearance of the membrane without affecting the degree of grafting and proton conductivity in the grafted areas. In fuel cell tests the structured membranes showed slightly lower performance due to 10% lower active area, but had a significantly higher lifetime.     

Transesterification of ketoesters with alcohols using polyaniline salts as catalysts

Polyaniline salts have been used as catalysts for the transesterification of ketoesters with alcohols in a process being reported for the first time. The catalytic use of polyaniline salts is feasible because of their easy preparation, recovery and reusability. Copyright © 2004 John Wiley & Sons, Ltd.     

Effect of solution acidity on the electrochemical behavior of Nafion—polyaniline films

Electrochemical behavior of Nafion–polyaniline films in acidic and neutral media is studied. Doping and degradation of the films are considered.Translated from Elektrokhimiya, Vol. 41, No. 2, 2005, pp. 224–227.Original Russian Text Copyright © 2005 by Andreev.This revised version was published online in April 2005 with corrections to the article note and article title and cover date.     

Morphology study of Nafion membranes prepared by solutions casting

The structures of Nafion membranes prepared by solutions casting from low aliphatic alcohols/water mixture solvents and N,N′‐dimethyl formamide (DMF) solvent were investigated using differential scanning calorimeter and small angle X‐ray scattering. The aggregation behavior of Nafion molecules in the casting solutions was also investigated using dynamic light scattering. We show that the morphology of membranes was strongly influenced by the conformations of Nafion molecules in the solutions. In aliphatic alcohol/water mixture solvents, which have a worse compatibility with Nafion backbones, the Nafion molecules aggregate and form fringed rod‐like structures. These primary rod‐like structures then aggregate again through fringed side chains to form secondary ionic aggregations. In DMF solvent, owing to its better compatibility with Nafion backbones, less Nafion molecules aggregate. The high degree of Nafion molecular aggregations in aliphatic alcohol/water mixture solvents leads to a high degree of hydrophobic and hydrophilic phase separation for membranes prepared by casting from Nafion/aliphatic alcohol/water solutions. However, the lower degree of molecular aggregations in DMF solvent results in a lower degree of hydrophobic and hydrophilic phase separation for membranes prepared by casting from Nafion/DMF solution. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3044–3057, 2005     

Structure and properties of the Nafion—polyaniline—palladium composite electrodes

Effect of conditions of deposition of palladium onto a composite polymeric film Nafion—polyaniline on the properties of the system thus obtained is studied. It is shown that the effect of the said conditions on the character of distribution of palladium in a polymer may be used when estimating electrocatalytic potentialities of such composites.Translated from Elektrokhimiya, Vol. 41, No. 2, 2005, pp. 213–218.Original Russian Text Copyright © 2005 by Andreev, Zolotarevskii.This revised version was published online in April 2005 with corrections to the article note and article title and cover date.     

Silicotungstic acid/organically modified silane proton-conducting membranes

Proton-conducting gels and membranes were made from an organically modified silane incorporating a heteropoly acid, i.e. silicotungstic acid. The ORMOSIL host was generated from a bis end-capped triethoxysilane chemically bonded via the urea bridges to (1) a long poly(propylene glycol) chain or (2) a long poly(dimethylsiloxane) chain. The heteropolyacid acted simultaneously as a source of mobile protons and as a catalyst, initiating the hydrolysis/condensation reactions of the sol–gel composite. In addition to the bis end-capped triethoxysilane network former, different alkoxysilanes were tested as network modifiers to optimize the gelation time, mechanical properties, ionic conductivity and the retention of the heteropolyacid during soaking of the membranes in water. Among alkoxysilane modifiers the most promising results were given by perfluorooctyltriethoxysilane and phenyltriethoxysilane. The conductivity of the membranes was up to 10^–2–10^–1 S cm^–1 at elevated temperatures and saturated humidity conditions. Fourier transform IR attenuated total reflection spectroscopy was used to follow the gelation of the samples and, in parallel to thermogravimetric/differential scanning calorimetry measurements, also the thermal stability of the membranes.     

纳米聚苯胺及聚苯胺/金复合材料的制备与表征

以氯金酸(HAuCl4)为氧化剂,在两种不同无机酸(HCl和H2SO4)的掺杂下,通过调节反应体系中混合溶剂的醇水比例,用一步氧化苯胺聚合法成功制备了不同形貌的纳米聚苯胺及聚苯胺/金复合材料.通过扫描电子显微镜(SEM)、紫外可见吸收光谱(UV-Vis)和红外光谱(FT-IR)对产物的形貌和结构进行了表征.在此基础上,进一步讨论了聚苯胺/金复合材料可能的形成机理.     

Preparation of benzyl acetate using polyaniline salts as catalysts ‐ Part II

Polyaniline salts were prepared by oxidizing aniline in presence of acid using benzoyl peroxide as an oxidizing agent. Polyaniline salt was used as catalyst for the esterification reaction of phenyl acetic acid with methanol. The process is being reported for the first time. Preparation of catalyst, recovery and reusability of the catalyst were found to be good. Copyright © 2004 John Wiley & Sons, Ltd.     

Synthesis and Properties of Novel Polyanions of Potential Antitumor Activity

A large number of naturally occurring polyanionic materials are known each of which possesses its own set of physiological properties. Within recent years, a wide variety of synthetic polyanions have become available, and investigators have compared their physiological properties with the naturally occurring polyanions. Perhaps, the most widely investigated synthetic polyanion is the 1:2 regularly alternating cycloco-polymer (DVE-MA) of divinyl ether (DVE) and maleic anhydride (MA), first discovered in these laboratories in 1951. This material has been investigated extensively, both from the standpoint of its chemical structure and its biological activity. Although certain aspects of its structure remain to be determined, it has been shown to possess a wide spectrum of biological activity. It possesses antitumor as well as other activities and is an interferon inducer. Many structural modifications of DVE-MA have been synthesized which also possess antitumor activity and interferon-inducing capability. A recent structural modification incorporated 5-fluorouracil (5-FU) into DVE-MA. This polymer is hydrolyzed readily to release 5-FU, and the material exhibited considerable activity against P388 lymphocytic leukemia. A novel series of polyanions have been synthesized via reactions of N-substituted triazolinediones with a variety of olefins and diene polymers. The synthesis and physiological properties of certain of these polyanions are discussed in this paper.     

Structure of composite films comprising Nafion, polyaniline, and palladium particles: A transmission electron microscopy study

Effect of conditions, under which a Nafion-polyaniline-palladium composite is formed, on the size and distribution of Pd particles in the composite is studied by transmission electron microscopy. It is shown that the size of most of the particles is a few nanometers. The number of the particles remains practically invariant following the composite degradation.     

Hydrogen sensors based on metal-insulator-semiconductor structures with a layer of a proton-conducting solid electrolyte

Application of solid electrolytes as undergate layers accelerates the response of a sensor at room temperature as compared with ordinary hydrogen sensors manufactured on the basis of the metal-insulator-semiconductor (MIS) structures with a palladium gate. The proton-conducting solid electrolytes under study include NAFION, zirconium hydrophosphate, and etherified polyvinyl alcohol (PVA) with heteropolyacids and phenoldisulfonic acid, which can be deposited under the platinum gate. Sensors based on the MIS structures with these solid electrolytes show a high sensitivity toward hydrogen (～120 mV per concentration decade). The response time τ_0.63 of a freshly manufactured sensor with a layer of zirconium hydrophosphate amounts to about 2 min. The maximum mechanical stability, especially at relative humidities in excess of 80% is intrinsic to sensors containing layers of PVA with heteropolyacids. The response time of such sensors is nearly 10 min.     

Preparation and characterization of proton-conducting sulfonated poly(ether ether ketone)/phosphatoantimonic acid composite membranes

The solid proton conductor, phosphatoantimonic acid, HSbP₂O₈ · H₂O was prepared by ion exchange of the corresponding potassium salt. The composite membranes of SPEEK with up to 40 wt% of HSbP₂O₈ · H₂O were prepared by introducing the solid proton conductor from the aqueous suspension. The composite membranes were characterized using FT-IR, powder X-ray diffraction, SEM, DSC/TGA. Thermal stability of the composite membranes was slightly lower than that of SPEEK. The composite membranes had higher water uptake when compared with SPEEK and the membranes exhibited controlled swelling up to 50 °C. The proton conductivity of the membranes was measured under 100% relative humidity up to 70 °C. The composite membranes showed enhanced proton conductivity up to 20 wt% of HSbP₂O₈ · H₂O and the conductivity was reduced with further increase of HSbP₂O₈ · H₂O loading. A maximum of four-fold increase in proton conductivity at 70 °C was observed for the composite membrane with 20 wt% of solid proton conductor.     

Effect of reaction conditions on film morphology of polyaniline composite membranes for gas separation

Composite membranes combining polyaniline as an active layer with a polypropylene support have been prepared using an in situ deposition technique. The protonated polyaniline layer with a thickness in the range of 90–200 nm was prepared using precipitation, dispersion, or emulsion polymerization of aniline with simultaneous deposition on top of the porous polypropylene support, which was immersed in the reaction mixture. Variables such as temperature, concentration of reagents, presence of steric stabilizers, surfactants, and heteropolyacid were found to control both the formation and the quality of the polyaniline layers. Both morphology and thickness of the layers were characterized using scanning electron microscopy. Selective separation of carbon dioxide from its mixture with methane is used to illustrate potential application of these composite membranes. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

The catalytic role of polyaniline salt in coumarins synthesis

Polyaniline‐sulfate salt acts as a simple and powerful polymer‐supported acid catalyst in the condensation of phenolic compounds and β‐keto esters into coumarin derivatives by a thermal heating process. This process is being reported for the first time. The catalytic use of polyaniline salt is quite feasible because of its easy preparation, activity, recovery, recyclability, stability and eco‐friendliness of the catalyst. Copyright © 2004 John Wiley & Sons, Ltd.     

Small‐angle neutron scattering investigation of structural changes in nafion membranes induced by swelling with various solvents

The structure of Nafion‐117 perfluorosulfonate ionomer membranes was investigated with small‐angle neutron scattering techniques. Structural changes induced by the swelling of the membranes with water, alcohols, and dipolar, aprotic solvents were monitored at solvent‐swelling levels ranging from approximately 2 vol % to greater than 50 vol %. Membranes swollen up to approximately 50 vol % solvent exhibited two scattering maxima, one known to be associated with ionic regions of the membrane structure and one known to be associated with correlation distances between crystalline regions in the membrane structure. The positions of both maxima shifted toward lower scattering vector values as the solvent content in the membrane increased. The shift in the position of both maxima was linearly related to the solvent volume fraction in the membrane. The Bragg spacings corresponding to both the ionic‐feature scattering maximum and the crystalline‐feature scattering maximum were plotted versus the solvent volume fraction in the membranes, and the data fit with linear regression. The slopes associated with the curves of the spacing versus the solvent volume fraction were greater for the crystalline‐feature spacing than for the ionic‐feature spacing for all solvents other than water; this was indicative of preferential segregation of nonaqueous solvents into regions of the structure not directly associated with the ionic scattering maximum. © 2002 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 40: 387–400, 2002; DOI 10.1002/polb.10092     

Grafting of polyaniline by a dynamic inverse emulsion polymerization technique onto reverse osmosis membranes as an antibiofouling agent

This study reports on the benefits of an in situ interfacial dynamic inverse emulsion polymerization process under sonication of aniline in the presence of a commercial reverse osmosis (RO) membrane. This polymerization method is simple and much faster (5‐15 min) than systems reported in the literature. During polymerization, the membranes are coated with polyaniline (PANI) as verified by high‐resolution scanning electron microscopy (HRSEM) images and Fourier‐transform‐infrared (FTIR) measurements. A colony‐counting antimicrobial activity test showed that whereas the reference RO membrane developed a large bacterial colony, the polyaniline‐coated RO membrane had no colonies at all. Surface resistivity was the lowest when the pH levels were below 6, which corresponded to the polyaniline‐grafted conductive layer. The membrane flow properties were only modified slightly as a result of the polyaniline grafting, compared with a pristine reference membrane.