Mass changes accompanying the pseudocapacitance of hydrous RuO2 under different experimental conditions

Pseudocapacitance reaction of hydrous ruthenium oxide was investigated by cyclic voltammetry combined with electrochemical quartz-crystal nanobalance (EQCN) in sulfuric acid as well as in neutral solutions of Na₂SO₄ and K₂SO₄. The ruthenium oxide electrode was prepared by attaching the ruthenium oxide particles on gold covered quartz electrode. The results show that there are different types of charge taking place simultaneously during the redox reaction of ruthenium oxide electrode. Their contribution to the overall charge depends on the experimental conditions. Depending on the potential and electrolyte used the redox reaction of ruthenium oxide is accompanied either by mass loss or by mass gain. The average molar masses of the species exchanged between the solid phase and the electrolyte solution depend on the potential and scan rate. The effect of Nafion™ top layer was also investigated. It has been found that it does not affect significantly the overall specific capacitance of ruthenium oxide electrode but the apparent molar masses of exchanged species decrease in comparison with the uncovered electrodes.     

Differential scanning calorimetry analysis of silicon‐containing and phosphorus‐containing segmented polyurethane. II Annealing effect

The effect of thermal annealing on the multiple endothermic behavior and morphological changes in the silicon‐containing and phosphorus‐containing segmented polyurethane (Si‐PU and P‐PU) has been studied by differential scanning calorimetry (DSC). In the amorphous hard segments of the Si‐PU and P‐PU polymers that were annealed below T2, both the T1 temperature, and magnitude of T1 endotherm increased linearly as a function of the logarithmic annealing time (log t_a). This result demonstrated that the endothermic behavior (T1 endotherm) is typical of enthalpy relaxation resulting from the physical aging of the amorphous hard segment. Furthermore, the P‐PU polymer was unstable than the Si‐PU polymer due to the fact that the phosphorus‐containing hard segment produce aged more easily. Dissociation of domains and enthalpy relaxation of hard segments for the Si‐PU polymer was associated with T2 endothermic behavior. However, the enthalpy relaxations of the T2 endothermic behavior for P‐PU polymer was absent, which could be attribute to the behavior of degradation in the temperature range of T2 endotherm. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 3502–3513, 2001     

Evaluation of a palladinized Nafion™ for direct methanol fuel cell application

Palladinized Nafion™ was prepared via ion-exchange and chemical reduction method. Palladium precursors and solvent systems determined the efficiency of the incorporation and distribution of nanoparticles. The tortuous thin Pd film was formed on the surface of membrane when Na⁺-Nafion™ and water were used. Pd nanoparticles enhanced the water uptake of Nafion™ and reduced its methanol uptake. And dispersed Pd nanoparticles in Nafion™ disturbed the proton conduction and methanol permeation simultaneously in Nafion™ cluster. In order to reduce methanol permeation of Nafion™ and keep its high conductivity, it was more efficient for Pd nanoparticles to distribute near the surface of membrane. Palladinized Nafion™ improved the performance of DMFC single cell operation by reducing the methanol permeation.     

Effects of stress and vapor exposure before and during aging on enthalpy relaxation of poly(vinyl chloride)

Enthalpy relaxations in glassy poly(vinyl chloride) following varied pre-aging treatments and under varied aging conditions have been compared through observations of sub-T_g endothermal DSC (differential scanning calorimetry) aging peaks. The extent of enthalpy relaxation for a fixed time and temperature of aging is progressively enhanced by the imposition and release of increasing mechanical stress before aging. The same effect is produced by sorption and desorption of increasing amounts of CO₂ or CH₃Cl vapor before aging. In contrast, the continued application of mechanical stress, or the presence of vapor, during the aging period suppresses enthalpy relaxation. The extent of suppression increases with increasing vapor pressure and solubility or increasing stress. These effects are interpreted as consequences of an increase in the enthalpy of the polymer under mechanical or sorptive stress and an enthalpy relaxation following the release of this stress. In addition to these effects on the DSC endotherm, a pronounced exotherm between the aging peak and T_g is observed for samples which have undergone shear yielding or orientation either before or during aging. This exotherm may be the result of release of stored strain energy during the DSC scan.     

Influence of history on the gas sorption,thermal, and mechanical properties of glassy polycarbonate

Glassy polycarbonate has been subjected to sub-glass-transition annealing and exposure to high-pressure CO₂. The subsequently measured solubilities of nitrogen, argon, and CO₂ in these specimens were found to be decreased by the former and increased by the latter. Annealing decreases the enthalpy of polycarbonate and mechanically embrittles it, whereas subsequent exposure to CO₂ erases these effects of annealing, can make the polymer even more ductile than the untreated material, and can apparently give it a higher enthalpy. Annealing densifies the glass, whereas the CO₂ treatment dilates it. The gas sorption observations are in accord with the dual-sorption model, and the effects of prior history are apparently the result of changes in the Langmuir capacity, which evidently is a sorption mechanism that exists as a result of the nonequilibrium nature, or excess volume, of the glassy state.     

A study of some equation‐of‐state parameters of poly(methylhydrosiloxane‐co‐dimethylsiloxane) with some solvents by gas chromatography

Trace amount of methyl acetate, ethyl acetate, tert‐butyl acetate, pentane, hexane, and heptane were passed through the chromatographic column loaded with poly(methylhydrosiloxane‐co‐dimethylsiloxane) coated on Chromosorb W. The retention diagrams of the solvents on the copolymer were plotted by means of specific retention volumes at temperatures between 40 and 80°C by inverse gas chromatography technique. In this study, some thermodynamic interaction parameters such as Flory–Huggins polymer–solvent interaction parameter, equation‐of‐state polymer–solvent interaction parameter, effective exchange energy parameter, and weight fraction activity coefficients at infinite dilution of the solvent were determined. Then, the exchange enthalpy parameter and entropy parameter were determined by using a relation for the enthalpy interaction parameter of the equation‐of‐state theory, which is arranged for the inverse gas chromatography conditions. Later, the partial molar heat of sorption and the partial molar heat of mixing were obtained. The solubility parameter of this copolymer was determined as 6.64 (cal/cm³)^1/2 at room temperature. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1627–1631, 2007     

Unforseen factors influencing Fe(III)‐containing cations sorption on strongly basic anion exchangers

The sorption and partial destruction of the Fe(III)‐containing compounds in the aqueous medium in strongly basic anion exchangers AV‐17 and Varion‐AD phase have been investigated. It is shown that partial destruction of the Fe (III) compounds in acidulated water (pH = 2) and in K₂SO₄, Fe₂(SO₄)₃ solutions takes place. With increasing of temperature up to 50°C, the desorption degree of the iron ions from polymer phase decreases. In dried polymer, the structural and electronic state of iron compounds, according to their magnetic susceptibility, remains stable for a long time. The sorption of the Fe(III)‐containing cations at 50°C during 12 h depends essentially on the sizes of polymer granules. Sorption increases with growing of polymer granules. For comparison of sorptional capacities, the sorption of Fe(III)‐containing cations was determined on different cation and anion exchangers. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Energetics of gas sorption in glassy polymers

The molar enthalpy for gas sorption in glassy polymers at a fixed concentration, often called the isosteric enthalpy of sorption, exhibits a clearly discernable minimum when plotted as a function of penetrant concentration. This unexpected behaviour has been observed in several glassy polymer systems including poly(ethylene terephthalate), polyacrylonitrile and polycarbonate. The behaviour can be modelled by analysing the temperature dependence of the various equilibrium parameters comprising the so-called dual mode sorption model for gas sorption in glassy polymers. The fundamental significance of the various enthalpies describing the temperature dependence of the Henry's law solubility constant, the Langmuir affinity constant and the Langmuir capacity constant are included in the discussion. Provision is made for non-ideal vapours and gases by introduction of the compressibility factor in the expression for the isosteric enthalpy. Application of relationships for calculating both the isosteric and the isothermal enthalpies of sorption is made to the case of CO₂ in poly(ethylene terephthalate) in the temperature range 35° to 115°C. These results and analyses complement the wealth of equilibrium and transport data which are consistent with the dual mode sorption model for penetrant sorption in glassy polymers.     

Sorption of Sulfur Dioxide on Hydrogen Form and Aluminum-Deficient Mordenites

Abstract

The SO₂ sorption characteristics of a commercial H-mordenite and an aluminum-deficient mordenite with a molar SiO₂/Al₂O₃ ratio of 75, prepared from the H-form, were investigated. The sorption isotherms and the reduced sorptive diffusivities were determined in the temperature range 298–358 K and at pressures up to 0.2 atm. It was found that the partially irreversible SO₂ sorption on the H-form became completely reversible by the removal of structural aluminum, while the absolute sorption capacity was decreased by 10–40% and the rate of sorption was improved by 50%.     

Behavior of Silver-Thiourea Complexes in Nafion Resin

Abstract

The behavior of silver-thiourea complexes in Nafion 117 resin was investigated with thiourea sorption and sodium-silver ion-exchange experiments. It was observed that the sorption of thiourea by the Ag-form of the ion exchanger was much higher than that obtained with the H- and Na-forms. The thiourea to silver molar ratio within the resin was found to be about 1.8. In the presence of thiourea, the fraction of silver species in the ion exchanger was about 20% greater than that in the absence of this ligand. The strong interaction between the silver-thiourea species and Nafion material may be attributed to the formation of an insoluble Ag₂T₃(SO₃R)₂ compound inside the ion exchanger.     

Thermal and pulse NMR analysis of water in poly(2-hydroxyethyl methacrylate)

Hydrophilic three-dimensional methacrylate polymer networks (hydrogels) were prepared from 2-hydroxyethyl methacrylate (HEMA) monomer and tetraethylene glycol dimethacrylate (TEGDMA) as crosslinker. The nature and states of water in these hydrogels were studied by differential thermal analysis and pulse NMR relaxation spectroscopy. The thermal studies showed no endotherm peak for ice melting in the lower water content (bound water region); there are two endotherms peaks for higher water content hydrogels near 0°C. The amounts of bound water, intermediate water, and bulklike (free) water in the hydrogels were determined from a quantitative analysis of the endotherms of the water melting transitions. The water structure ordering in the hydrogels were discussed in terms of the fusion entropy and enthalpy obtained from the endotherm. Nuclear magnetic relaxation spectroscopy was also used to understand the mobilities of the water protons in the hydrogels and the interaction of water molecules with the gel networks. The measured spin-lattice relaxation time (T₁) values for water protons in the hydrogels are greatly reduced compared to that of liquid water. The measured values of spin–spin relaxation times (T₂) of water protons in the hydrogels are approximately 10 times less than that of T₁ and are almost constant in the region of bound water content. Beyond the bound water content region in the hydrogels, the T₂ values rapidly increase as the water content increases.     

Mesomorphic polyblends of poly(p-phenylene terephthalamide) and poly(4,4′-terephthanilide adipamide)

A simultaneous dissolution of two lyotropic polyamides, poly(p-phenylene terephthalamide) (PPTA) and poly(4,4′-terephthanilidc adipamide) (PTAd), in a concentrated H₂SO₄ (1 to 1.5% wt) produced an isotropic single phase solution. The crystallinity of PPTA/PTAd blends confirmed formation of a mesomorphic polyblend to the molecular level. With increasing concentration, solutions of these PPTA/PTAd blends in 100% H₂SO₄ showed a sequential phase change typical of a single lyotropic polymer. Further, the ternary solution exhibited a wider biphase range than both binary solutions of PPTA/100% H₂SO₄ and PTAd/100% H₂SO₄. Dry-jet wet spinning of anisetropic solution of this ternary composition with a PTAd weight fraction less than 0.5 enabled us to obtain PPTA/PTAd blend fibers. Including a PTAd weight fraction of 0.1-0.15 reduced both the orientation angle and fibrillation. The particular blend fiber with a PTAd weight fraction of 0.15 exhibited a synergistic effect on the mechanical properties.     

Sorption of sulphur dioxide by indoor surfaces II. Wood

The sorption of sulphur dioxide by untreated wood samples has been investigated at a concentration of 90 μg/m³ by use of ³⁵SO₂. The softwoods sorbed less sulphur dioxide than the hardwoods and the sites of sorption were different in each class. Most of the sorbed sulphur dioxide was found in the outermost 0.05 mm of each sample and a large portion of it was water-soluble. The possible role of sulphur dioxide in the weathering of woods is discussed.     

Thermal behaviors of polystyrene plasticized with compressed carbon dioxide in a sealed system

The thermal behavior of polystyrene (PS) plasticized with compressed carbon dioxide (CO₂) was studied using differential scanning calorimetry with a high‐pressure stainless steel pan in a sealed system. The technique proved to be a simple and convenient way to study the thermal behavior of a polymer plasticized with compressed CO₂ at pressures up to 100 atm, which covers both the gas and supercritical states. A sharp fall in the decrease rate of the glass transition temperature (T_g) under conditions near the critical point of compressed CO₂ was firstly observed, which corresponded with the solubility of CO₂ in PS. Since the system is scaled, which results in a stable pressure at a certain temperature, it is more suitable to study the effect of annealing. An endotherm was detected after the PS was annealed at a temperature below its T_g under compressed CO₂. The enthalpy of this endotherm increased linearly with increasing logarithm of annealing time under a certain pressure. The endotherm was affected by two thermodynamic equilibrations at a temperature below its T_g: (i) enthalpy relaxation of the PS; and (ii) the absorption/desorption of CO₂. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Analysis of the moisture sorption behavior of amorphous drug–polymer blends

Hydrophobic drugs are often formulated with hydrophilic polymers to form miscible blends called amorphous solid dispersions. The interaction of moisture with these blends is an important topic, both from stability as well as processing perspectives. In this study, the moisture sorption profiles of four different drug–polymer blends, [felodipine–poly(vinylpyrrolidone) (PVP), indomethacin–PVP, felodipine–hypromellose (HPMC), and felodipine–hypromellose acetate succinate (HPMCAS)] were experimentally determined at 25°C, and analyzed using various mathematical models. It was found that the moisture sorption profiles of the drug–polymer blends could not be reconstructed using the weight‐averaged sum of the moisture sorbed by each of the components. Application of the Flory–Huggins model for ternary systems to extract drug–polymer interaction parameter (χ₂₃) values using known values of water–drug and water–polymer interaction parameters led to ambiguous conclusions about the systems' thermodynamics. χ₂₃ values extracted for felodipine–PVP and indomethacin–PVP using this model ranged from ?9.6 to 26.9 and ?20.4 to 22.0, respectively. It is thought that the presence of specific drug–polymer interactions changed the water–drug and the water–polymer interactions in the system. Combined with the mathematically small contribution from the term encompassing χ₂₃ to the predicted amount of moisture sorbed by the drug–polymer blends, it was concluded that this method cannot be used to unambiguously determine drug–polymer interaction parameters in solid dispersions. Instead, a model with a mean interaction parameter (χ_1,23) that considers the drug and the polymer in the blend as a single unit was found to better describe the changing affinity of water for the solid matrix with a change in composition or polymer type. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Adsorption of Some Atmospherically Important Molecules onto Large Water Clusters: SO2, SO3, HCl,and ClONO2

The adsorption of a range of atmospherically important molecules (SO₂, SO₃, HCl, and ClONO₂) on large water clusters have been studied using a supersonic molecular beam expansion to generate water clusters containing 50–450 water molecules. SO₂ and HCl were found to stick with low efficiency to the water cluster, retaining their chemical identity. In contrast, both SO₃ and ClONO₂ undergo heterogeneous reactions on the surface of the water cluster forming, respectively, H₂SO₄ and HOCl with HNO₃. For SO₃, calculations show that the large barrier that exists in the gas-phase to the reaction of SO₃ with water is removed for water clusters of a sufficient size because of stabilization of the transition state by solvation. For ClONO₂, the barrier to reaction is much larger and cannot be removed by solvation for any size cluster. In this case, it is likely that reaction takes place on the water cluster by the ionic dissociation of ClONO₂ in a similar manner to that observed for ClONO₂ on ice films.     

Analysis of polyethylene surface sulfonation

Attachment of ? SO₃H groups onto the surface of polymers by treatment with fuming sulfuric acid is a well-known procedure. In the present study we compare the number of ? SO₃H groups per unit area measured by a number of methods including weight gain, thickness, FT-IR transmittance spectra, FT-IR surface spectra with ATR method, sodium exchange, and p^H measurement of water in contact with the polymer surface. It can be shown that, under the chosen conditions, i.e., room temperature and 32% SO₃ in H₂SO₄, oxidation of PE is the main reaction, while sulfonation accounts for less than 20% of the weight gained during reaction. Differences in the reactivity of high density and low density polyethylenes are discussed. Deprotonation in water compared with H⁺ /Na⁺ exchange indicates a poor penetration of sodium ions into deeper layers of the polymer. © 1994 John Wiley & Sons, Inc.     

Plasticization of chitosan membrane for pervaporation of aqueous ethanol solution

The process of pervaporation in which two components diffuse through a nonporous polymer membrane was modelled when one of the penetrants can exert a plasticization action to the membrane material. Thereat a phenomenological model was employed for describing the plasticization effect on the diffusivities for penetrants in the membrane. The sorption equilibria and permeation fluxes for aqueous ethanol solutions in a chitosan membrane were measured, and the permeation fluxes for water were compared with those predicted by the proposed model. The concentration of sorbed water was linear with its weight fraction (x₄) in the feed solution, whereas the permeation flux of water was. affected by the plasticization action of sorbed water to the polymer. This plasticization effect on the diffusion process can be simulated in terms of the proposed phenomenological model.     

Measurements of proton conductivity in the active layer of PEM fuel cell gas diffusion electrodes

This paper reports further studies to understand and optimize the Membrane and Electrode Assembly (MEA) structure in Polymer Electrolyte Membrane Fuel Cells (PEMFCs). The effective proton conductivity in the active catalyst layer was measured as a function of its composition, which consisted of platinum catalyst on carbon support (E-Tek) and Nafion® polymer electrolyte (DuPont de Nemours). The conductivity was calculated from the resistance added to a standard MEA by the addition of an inactive composite layer in the electrolyte path between the anode and cathode. The specific conductivity of the active layer was found to be proportional to the volume fraction of Nafion® in the composite mixture, following the relationship κ^eff_H⁺≈0.078_Nafion+0.004 S cm⁻¹. Modeling studies showed that this ionic conductivity limits the utilized active layer thickness to 20–25 μm.     

In situ characterization of moisture sorption/desorption in thin polymer films using optical waveguide spectroscopy

The kinetics of moisture sorption/desorption in poly(terephthalate-co-phosphate) thin films was investigated in situ at T = 25 °C using optical waveguide spectroscopy (OWS). At low water activities, Fickian diffusion was observed for the initial phase of the sorption process, while at high activities, due to the clustering of water, a complex sorption behavior was found. The moisture sorption isotherms were analyzed according to both the Zimm and Lundberg model as well as the Brown model, which suggests the formation of clusters of water molecules in poly(terephthalate-co-phosphate) at water activities of α₁ = 0.58 or higher. The water diffusion coefficient decreases with increasing water activity, which also suggests water cluster formation. A biphasic desorption behavior was also observed upon decreasing the water activity from α₁ = 1 to 0. This study demonstrated the unique advantages of OWS in characterizing in situ the sorption/desorption behavior of penetrants in polymer thin films.