Comparison of three models for permeation of CO2/CH4 mixtures in poly(phenylene oxide)

Two models for the permeability of pure gases have been extended to include binary gas mixtures. The first is an extension of a pure gas permeability model, proposed by Petropoulos, which is based on gradients of chemical potential. This model predicts the permeability of components in a gas mixture solely on the basis of competition for sorption sites within the polymer matrix. The second mixed gas model follows an earlier analysis by Barrer for pure gases which includes the effects of saturation of Langmuir sites on the diffusion as well as the sorption processes responsible for permeation. This generalized “competitive sorption/diffusion” model includes the effect of each gas component on the sorption and diffusion of the other component in the mixture. The flux equations from these two models have been solved numerically to predict the permeability of gas mixtures on the basis of pure gas sorption and transport parameters. Both the mixed gas Petropoulos and competitive sorption/diffusion model predictions are compared with predictions from the earlier simple competitive sorption model based on gradients of concentration. An analysis of all three models is presented for the case of CO₂/CH₄ permeability in poly(phenylene oxide) (PPO). As expected, the competitive sorption/diffusion model predicts lower permeability than either of the models which consider only competitive sorption effects. The permeability depression of both CO₂ and CH₄ predicted by the competitive sorption/diffusion model is roughly twice that predicted by the competitive sorption model, whereas the mixed gas Petropoulos model predictions for both gases lie between the other two model predictions. For the PPO/CO₂/CH₄ system, the methane permeability data lie above the predictions of all three models, whereas CO₂ data lie below the predictions of all models. Consequently, the competitive sorption/diffusion model gives the most accurate prediction for CO₂, while the simple competitive sorption model is best for methane. The effects of mixed gas sorption, fugacity, and CO₂-induced dilation were considered and do not explain the inaccuracies of any of the models. The relatively small errors in mixed gas permeability predictions using either of the three models are likely to be related to “transport plasticization” of PPO owing to high levels of CO₂ sorption and its effect on polymer segmental motions and gas diffusivity.     

Pure and mixed gas acetone/nitrogen permeation properties of polydimethylsiloxane [PDMS]

The permeability of polydimethylsiloxane [PDMS] to acetone, nitrogen, and acetone/nitrogen mixtures has been determined at 28°C. In pure gas experiments, the permeability of PDMS to nitrogen was 245 × 10⁻¹⁰ cm³(STP) · cm/cm² · s · cmHg and was independent of pressure. The permeability of PDMS to acetone vapor increased exponentially with increasing acetone pressure. PDMS is much more permeable to acetone than to nitrogen; acetone/nitrogen selectivity increases from 85 to 185 as acetone partial pressure in the feed increases from 0 to 67% of saturation. In mixed gas permeation experiments, the nitrogen permeability coefficient is independent of acetone relative pressure and is equal to the pure gas permeability coefficient. The acetone permeability coefficient has the same value in both mixed gas and pure acetone permeation experiments. Average acetone diffusivity in PDMS, determined as the ratio of permeability to solubility, decreases with increasing acetone concentration due to mild clustering of acetone in the polymer (because acetone is a poor solvent for PDMS) and changes in the polymer–penetrant thermodynamic interactions which influence diffusion coefficients. A Zimm–Lundberg analysis of the acetone sorption isotherm is also consistent with acetone clustering in PDMS. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36 : 289–301, 1998     

Thermodynamic Characteristics of Resolvation of Bromide Ions in Water–Dimethyl Sulfoxide Mixtures

Real and chemical thermodynamic characteristics of resolvation of bromide ions in water–dimethyl sulfoxide mixtures and a surface potential of dimethyl sulfoxide are presented and analyzed. The data are obtained by the method of Volta potential differences. The real thermodynamic characteristics of the bromide ion transport are positive (as those of the chloride ion studied earlier). This is due to structural rearrangement of the surface layer at the solution/gas interface when passing from water to water–organic substance mixtures. According to an analysis of the chemical energy of the bromide ion resolvation, anions that are capable of forming hydrogen bonds with proton-donor solvents are weakly solvated in aprotic solvents.     

Measuring diffusivity in supercooled liquid nanoscale films using inert gas permeation. I. Kinetic model and scaling methods

We describe in detail a diffusion model used to simulate inert gas transport through supercooled liquid overlayers. In recent work, the transport of the inert gas has been shown to be an effective probe of the diffusivity of supercooled liquid methanol in the experimentally challenging regime near the glass transition temperature. The model simulations accurately and quantitatively describe the inert gas permeation desorption spectra. The simulation results are used to validate universal scaling relationships between the diffusivity, overlayer thickness, and the temperature ramp rate for isothermal and temperature programmed desorption. From these scaling relationships we derive simple equations from which the diffusivity can be obtained using the peak desorption time or temperature for an isothermal or set of TPD experiments, respectively, without numerical simulation. The results presented here demonstrate that the permeation of gases through amorphous overlayers has the potential to be a powerful technique to obtain diffusivity data in deeply supercooled liquids.     

Thermodynamics and transport properties of monatomic systems from the MSK potential

Shukla, K.P., Luckas, M., Ameling W. and Lucas, K., 1986. Thermodynamics and transport properties of monatomic systems from the MSK potential. Fluid Phase Equilibria, 28: 217–231.The MSK potential has been used to correlate and extrapolate the thermodynamic and transport properties of various monatomic systems. The statistical mechanical equations in the dilute gas range were solved in the standard way. In the liquid range, hard-sphere perturbation theory and comoputer simulations were used, taking non-additive three-body forces and quantum effects into account. Very satisfactory results are obtained for pure systems and mixtures over the whole density range, lending support to the potential function, its particular parameters and the combination rules for the unlike interactions.     

Real and chemical solvation energies of individual ions in solution

On the basis of the proposed concept of real thermodynamic properties for individual ions in solution, the real thermodynamic properties of transport (resolvation) for various ions (sodium, potassium, chloride, bromide, and iodide) from water to mixtures of water with ethyl, n-propyl, and isopropyl alcohols, acetone, acetonitrile, dimethylsulfoxide, and dimethylformamide are determined by the method of Volta potential differences. Values of the chemical thermodynamic properties of transport of the ions under investigation are determined on the basis of previously calculated values of surface potentials of the solvents mentioned above. A comparative analysis of the values obtained is carried out, and characteristics of the solvation of ions of different sign are established as functions of their nature relative to the physicochemical and structural properties of the solvents. The satisfactory agreement of the data obtained on the basis of the total Gibbs energy of transport of the ions under investigation in the indicated solvents with literature data is the criterion of correctness for the scientific material presented in this paper.     

BaCe0.5Zr0.4La0.1O3－α陶瓷的制备及其电性能

以高温固相反应法合成了BaCe0.5Zr0.4La0.1O3－α陶瓷. 粉末XRD结果表明, 该陶瓷材料为单一钙钛矿型BaCeO3斜方晶结构, 在高温下、CO2或水蒸气气氛中具有较高的稳定性. 以陶瓷材料为固体电解质、多孔性铂为电极, 用交流阻抗谱技术测定了材料在500～900 ℃下, 不同气体气氛中的电导率; 用气体浓差电池方法测定了材料在干燥空气、湿润空气和湿润氢气气氛中的离子迁移数, 研究了材料的离子导电特性. 结果表明, 在500～900 ℃下, 干燥或湿润的气体气氛中, 随着温度升高和氧分压增大, 材料的电导率均增大. 在干燥空气中, 陶瓷材料的氧离子迁移数为0.685～0.147, 是一个氧离子与电子空穴的混合导体. 在湿润空气中, 陶瓷材料的质子迁移数为0.001～0.006, 氧离子迁移数为0.618～0.164, 是一个质子、氧离子和电子空穴的混合导体. 在湿润氢气中, 500～700 ℃温度范围内, 陶瓷材料的质子迁移数为1, 是一个纯的质子导体; 而在800～900 ℃温度范围内, 陶瓷材料的质子迁移数为0.957～0.954, 是一个质子与电子的混合导体, 质子电导占主导.     

The swelling interface number as a criterion for prediction of diffusional solute release mechanisms in swellable polymers

When a glassy polymer containing a uniformly dispersed solute is brought in contact with a penetrant, solute diffusion will be associated with the transport mechanism and penetration velocity of the penetrant in the polymer. Analysis and prediction of mechanisms of diffusional solute release may be obtained through a new dimensionless number, the swelling interface number, Sw, which compares the relative mobilities of the penetrant and the solute in the presence of macromolecular relaxations in the polymer. It is shown that a sufficient and necessary criterion for time-independent diffusional solute release rates from these swellable systems is that the Sw be smaller than 10^?2. The swelling interface number Sw may be related to easily determined structural and thermodynamic parameters of the solute/polymer/penetrant system. Preliminary experimental results of dynamic water swelling of poly(2-hydroxyethyl methacrylate-co-methyl methacrylate) and diffusional release of theophylline from initially glassy copolymers show that decreasing values of Sw are related to increased pseudo-case-II transport kinetics of the solute.     

Concentration-dependent transport of gases and vapors in glassy polymers: II. Organic vapors in ethyl cellulose

The solution (sorption) and transport of acetone, benzene, and methanol vapors in ethyl cellulose have been studied by Barrer, Barrie and Slater [5, 6] over a range of temperatures and penetrant concentrations. The solubility isotherms for the three penetrants as well as the diffusivity and permeability data for acetone reported by these investigators are analyzed in terms of a “dual-sorption” model with partial penetrant immobilization [3], assuming that the diffusion coefficient is concentration dependent [4].     

Response of a glass/phenolic composite to high temperatures

Determining the response of composite phenolic materials to fire remains a major unsolved problem that is important for high consequence safety analysis. Difficulties arise when thermophysical property measurements are obscured by decomposition reactions. This article presents several decomposition experiments and models for a phenolic resin impregnated into chopped 1.27-by-1.27 cm glass fabric. The thermal response of the material was measured using thermogravimetric analysis (TG), differential scanning calorimetry (DSC), and laser flash diffusivity (LFD). The TG data was used to develop a 5-step decomposition mechanism describing mass loss due to reaction; the DSC data was used to describe the energy changes associated with these reactions; and the LFD data was used to describe energy flow into the decomposing material. An effective thermal conductivity model was used to partition energy transport by gas conduction, solid conduction, and diffusive radiation. The dynamic gas volume fraction is treated as a field variable to extrapolate thermal transport properties at high temperatures where decomposition is prevalent. These various models have been implemented into a finite element response model with an example calculation that includes uncertainty.     

The concentration dependence of the diffusion and permeability in a homogeneous membrane

For the sorption and diffusion coefficient dependence on the concentration of the penetrant the transport properties of a homogeneous medium are calculated. The diffusion current is assumed to be proportional to the negative gradient of the chemical potential. This is in contrast with the first Fick's law that assumes this current to be proportional to the negative gradient of the concentration of the penetrant. The difference between the two cases depends on the concentration dependence of the sorption coefficient. In a homogeneous membrane the chemical potential formulation leads to an equation which is very similar to the Fickian expression. The apparent diffusion coefficient, however, depends not onlly on the transport resistance but also on the deviation of the sorption coefficient from constancy.     

New approach to defining thermodynamic surface tension of solids

Using either the chemical potential of the immobile component of a solid dissolved in a fluid phase or the corresponding component of the tensor of chemical potential in solid phase, a new concept of the grand thermodynamic potential of solid-fluid two-phase system is proposed. For a planar interfacial surface, this makes it possible to generalize the notion of thermodynamic surface tension σ introduced by Gibbs that has the meaning of the formation work of a unit surface. This tension is determined as the specific surface excess of the grand thermodynamic potential. This definition of the thermodynamic surface tension does not depend on the position of the dividing surface and is common for fluids and solids. It is shown that, at the arbitrary position of dividing surface, the difference between thermodynamic σ and mechanical @[gamma] surface tensions for solid surface is determined by the nonuniformity of the tensor of chemical potential in a solid, as well as by its anisotropy in the bulk of solid phase.     

Ba0.9La0.1Ce0.7Zr0.2Nd0.1O3-α陶瓷的化学稳定性和离子导电性

用高温固相反应法制备了Ba0.9La0.1Ce0.7Zr0.2Nd0.1O3-α陶瓷。粉末X-射线衍射(XRD)结果表明,该材料为单一钙钛矿型BaCeO3斜方晶结构,在高温下、CO2或水蒸气气氛中具有较高的稳定性。在500～900℃温度范围内,分别用交流阻抗谱技术和气体浓差电池方法研究了材料在不同气体气氛中的离子导电特性,并与Ba0.9Ca0.1Ce0.9Nd0.1O3-α材料的导电特性进行了比较。结果表明,在500～900℃温度范围内,干燥和湿润的氢气、氮气、空气和氧气气氛中,材料的电导率均随着温度升高和氧分压增加而增加,且材料在湿润气氛中的电导率稍高于相应的干燥气氛中的电导率(氢气气氛中则相反)。在湿润氢气中,材料的质子迁移数为1,是一个纯的质子导体;在干燥空气中,材料的氧离子迁移数为0.087～0.155,是一个氧离子与电子空穴的混合导体;在湿润空气中,材料的质子迁移数为0.001～0.004,氧离子迁移数为0.160～0.198,是一个质子、氧离子和电子空穴的混合导体。材料在干燥和湿润空气中的氧离子电导率均高于相同条件下Ba0.9Ca0.1Ce0.9Nd0.1O3-α材料的氧离子电导率。     

Aging of quenched polypropylene

Structural changes occurring during the aging of polypropylene quenched from the melt have been investigated by measurements of gas transport parameters and mechanical properties. Major changes in diffusion and sorption behavior during the first 30 hr of aging at room temperature were found to be strongly dependent on the atomic size of the inert gas penetrants. Tensile mechanical properties increased with aging time, while resilience and mechanical damping showed more complex behavior. The interpretation of the combined results suggests that the aging process may involve molecular rearrangements generally comparable to those for secondary crystallization processes, but within domains comparable in size to that of the smaller penetrant species. The relaxation of a residual stress distribution related to nonuniform plastic flow during quenching may be superimposed on the rearrangement phenomena.     

Chemical potentials,concentration fluctuations,etc., in binary metal alloys

Abstract

Relationships among transport parameters and the mean square composition fluctuations as determined by measurements of the chemical potentials are described for a variety of binary liquid metal alloys. The measurement of the chemical potential is described and the thermodynamic basis for the analysis given in terms of the concentration correlation functions as well as more traditional thermodynamic parameters. Alloys involving group III_A metals with Te are used as an example     

Thermodynamics of Resolvation of Sodium and Potassium Ions in Water–Dimethylformamide

The real primary medium effect of sodium and potassium ions and the real Gibbs energy of transfer of these ions from water into a mixed water–dimethylformamide (DMF) solvent are determined using the method of Volta potential differences at 298.15 K. For DMF, the surface potential at the solvent/gas interface is found to equal –0.434 V. Based on this value, chemical thermodynamic characteristics of the ions are calculated. The thermodynamic characteristics for resolvation of cations are compared with those for anions in the mixtures under investigation obtained earlier.     

Thermodynamic aspects of ion intercalation in KhFek[Fe(CN)6]l*mH2O compounds: application to the Everit's Salt/Prussian blue transition

The K(+) reversible processes for ion exchange in K(h)Fe(k)[Fe(CN)(6)](l)*mH(2)O host compounds (Prussian Blue) were thermodynamically analyzed. A thermodynamic approach was established and developed based on the consideration of a lattice-gas model where the electronic contribution to the chemical potential is neglected and the ion-host interaction is not considered. The occupation fraction of the intercalation process was calculated from the kinetic parameters obtained through ac-electrogravimetry in a previous paper. In this way, the mass potential transfer function introduces a new way to evaluate the thermodynamic aspect of intercalation. Finally, based on the thermodynamic approach, the energy used to put each K(+) ion into the host material was calculated. The values were shown to be in good agreement with the values obtained through transient techniques, for example, cyclic voltammetry. As a result, this agreement between theory and experimental data validates the thermodynamic approach considered here, and for the first time, the thermodynamic aspects of insertion were considered for mixed valence materials.     

Water transport in a polyketone terpolymer

Water transport in a polyketone terpolymer was analyzed performing both sorption and permeation experiments. Water vapor sorption tests were conducted at four temperatures (35, 45, 55, and 65°C) and at several activities. The analysis of sorption isotherms revealed the occurrence of water clustering. A reduction of the endothermicity of mixing as the amount of sorbed water increased was observed which is consistent with significant association of penetrant molecules in the polymer. Permeation experiments performed at 35°C at upstream pressures ranging from 4 to 25 Torr showed evidence of a reduction in water diffusivity as function of sorbed water concentration which is a typical indication of penetrant aggregation. © 1995 John Wiley & Sons, Inc.     

Solubility,diffusivity, and mobility of n-pentane and ethanol in poly(1-trimethylsilyl-1-propyne)

The diffusion coefficient of ethanol and of n-pentane in PTMSP, at 27°C, was measured as a function of concentration up to a penetrant content of about 12% by weight, for polymer samples obtained through different processes; differential sorptions and desorptions with vapor phases were considered. In the case of ethanol a nonmonotonous behavior was observed for the diffusivity, while in the case of n-pentane the same property was found to monotonously decrease with increasing the penetrant content. The sorption isotherms were also reported, indicating that n-pentane exhibits a typical dual mode behavior, while ethanol follows an unusual s-shape curve. The chemical potential of the dissolved penetrants, calculated directly from the isotherms, shows the very different importance of the energetic interactions of the two penetrants with the polymer units. In spite of the remarkably different concentration dependencies observed for both solubility and diffusivity of the two penetrants, the mobility factors are in both cases monotonously decreasing with the penetrant concentration, and follow very similar trends. The significant differences observed for the concentration dependence of the diffusion coefficients are, thus, associated to the thermodynamic contributions, which are very different for n-pentane and ethanol. Different polymeric films, obtained through different solvent evaporation processes, show quite different solubility, diffusivity and mobility for both ethanol and n-pentane. On the other hand, the ratio between the mobility of the two penetrants as well as the slope of mobility as function of the concentration remains the same for all the different samples inspected. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 2245–2258, 1997