Diffusion and desorption of CO2 in foamed polystyrene film

Based on the existence of the pores in foamed polystyrene (PS), foamed‐non‐Fickian diffusion (FNFD) model was proposed, for the first time, to regress the desorption data obtained by gravimetric method. Results showed that FNFD model could accurately describe the diffusion behavior of CO₂ out of foamed PS, and well predict the solubility of CO₂ in foamed PS. The characterization of scanning electron microscopy indicated that there were abundant pores in the foamed PS, and the pores store most of CO₂, which would diffuse in the pores, adsorb to the wall of the pores, penetrate across walls of the pores, diffuse in the matrix of PS, and desorb out of PS. The mass of CO₂ in the pores of foamed PS was expressed as a function of foaming pressure and temperature according to foaming kinetics. Results showed that the values calculated by this function agreed well with the values obtained from the FNFD model. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45645.     

Metal-induced polymer framework membrane with high performance for CO2 separation

In this study, a novel porous material, that is, metal-induced polymer framework-1 (MPF-1) was synthesized using Zn(NO₃)₂·6H₂O and a high-molecular weight PVAmacid. MPF-1 has two structural advantages that help to create CO₂ separation membranes with simple fabrication procedure and high performance. First, MPF-1 is a high-molecular weight polymer with certain flexibility, and thus having good membrane-forming ability. Second, MPF-1 has small and uniform distributed pores, and contains amine groups those can react with CO₂ molecules reversibly. Therefore, CO₂ molecules can preferentially adsorb on pore walls of MPF-1 and transport across the pores by monomolecular surface diffusion, while most of N₂, CH₄, or H₂ molecules are excluded out the pores. The MPF-1 was employed to fabricate a microporous membrane by coating the MPF-1 dispersions on a polysulfone ultrafiltration membrane. CO₂ permeance and selectivity of the membrane keep almost unchanged with the feed pressure increasing from 0.11 to 1.0 MPa. © 2018 American Institute of Chemical Engineers AIChE J, 65: 239–249, 2019     

CO2 removal by single and mixed amines in a hollow‐fiber membrane module—investigation of contactor performance

This work investigates CO₂ removal by single and blended amines in a hollow‐fiber membrane contactor (HFMC) under gas‐filled and partially liquid‐filled membrane pores conditions via a two‐scale, nonisothermal, steady‐state model accounting for CO₂ diffusion in gas‐filled pores, CO₂ and amines diffusion/reaction within liquid‐filled pores and CO₂ and amines diffusion/reaction in liquid boundary layer. Model predictions were compared with CO₂ absorption data under various experimental conditions. The model was used to analyze the effects of liquid and gas velocity, CO₂ partial pressure, single (primary, secondary, tertiary, and sterically hindered alkanolamines) and mixed amines solution type, membrane wetting, and cocurrent/countercurrent flow orientation on the HFMC performance. An insignificant difference between the absorption in cocurrent and countercurrent flow was observed in this study. The membrane wetting decreases significantly the performance of hollow‐fiber membrane module. The nonisothermal simulations reveal that the hollow‐fiber membrane module operation can be considered as nearly isothermal. © 2014 American Institute of Chemical Engineers AIChE J, 61: 955–971, 2015     

Modeling of Aniline Removal by Reverse Osmosis Using Different Membranes

The behavior of different reverse osmosis membranes, namely, HR98PP, SEPA‐MS05, and DESAL‐3B, was compared with the one predicted by a solution‐diffusion model. This model assumes that the membrane has a homogeneous, nonporous surface layer and uses two main parameters, permeate concentration C_p and volumetric permeate flux Q_p, to characterize the membrane system. In order to calculate these parameters, the theoretical values of water and solute permeability constants, A_w and B_s, and the osmotic pressure coefficient, Ψ, were initially determined. Using the software Sigma Plot V 10.0, accurate values of Ψ, Q_p, and C_p were only obtained for the DESAL‐3B membrane, i.e., the selected solution‐diffusion model can be applied to this membrane.     

Insight into the intraparticle diffusion of residue oil components in catalysts during hydrodesulfurization reaction

Well‐defined and uniform pore structure catalysts were used to study the intraparticle diffusion of fractionated Saudi vacuum residue under hydrodesulfurization (HDS) reaction conditions. HDS rates of residue oil cuts with different molecular weights are determined as functions of pore size, temperature, and pressure in a trickle‐bed reactor. Credible intrinsic and bulk diffusivities of organosulfur compounds in residue oil were obtained for the first time, from the apparent and intrinsic reaction kinetic constants. Intrinsic diffusivities ranged from 2 × 10^?7 to 8 × 10^?7 cm²/s for the residual oil molecules; diffusivity decreases with increasing molecular weight of the residual oil. The intrinsic diffusivity for molecular weights ～1000 Daltons increases with pore size for pores <70 nm, but is nearly independent of pore size for pores >70 nm. The diffusivity dependences on pore size and molecular weight suggest that the onset of restricted diffusion occurs for ratios of molecular diameter to pore diameter of ～0.04. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3267–3275, 2014     

Infusion of Ag‐Ion from Aqueous Solution into Solid Calcium Phosphate of Hydroxyapatite (HA) Crystal Structure

In contrast to extensive literature concerning Ag incorporation in hydroxyapatite, HA, while the phosphate approximated to stoichiometry of Ca₁₀(PO₄)₆(OH)₂, with added Ag has been precipitating from an aqueous solution, the paper presents Ag incorporation through Ag ion infusion from AgNO₃ solution into solid HA pressed in pellet and ignited at 800°C. After Ag ions infused into the HA‐solid (crossed the interfacial solution‐solid boundary), they diffused across the crystal structure to a depth of time‐dependent several mm. The path of Ag diffusion in the solid HA was recorded using SEM‐EDS point analyses of Ag, Ca, P, EDS‐linear analyses of those elements, and elemental mapping. Time‐dependent concentrations of Ag⁺, Ca²⁺, and PO₄^3? in AgNO₃ solutions were also analyzed. The appearance of Ag in the crystalline HA with simultaneous local depletion in Ca and phosphate recorded as P, observed by EDS with simultaneous appearance of Ca²⁺ and PO₄^3? ions and a decrease in Ag⁺ concentration in AgNO₃ solution led the authors to a conclusion that Ag⁺ for Ca²⁺ substitution supported by PO₄^3? charge balancing in the crystalline HA was in process. The HA particles in the section of the pellet without Ag had a uniform shape and size approximated to 300–400 nm. SEM image of the HA solid section, where Ag ions appeared was characterized by irregular aggregates of smaller crystals with sporadically present large, shaped in prism blocks identified by the XRD as Ag₃PO₄.     

Humid aging of polyetherimide. I. Water sorption characteristics

The sorption and desorption kinetics of water into polyetherimide (ULTEM 1000) were studied at various temperatures ranging from 20 to 100°C. The water equilibrium concentration increases slightly with temperature from 1.39% (by weight) at 20°C to 1.50% at 100°C. The solubility coefficient, S, calculated from these data, and the water vapor pressure decrease with temperature. The calculated heat of dissolution H_s is close to −43 kJ mol⁻¹, which explains the low effect of temperature on the equilibrium concentration. The diffusion coefficient, D, varies from about 1.10⁻¹² m² · s⁻¹ at 20°C to about 16.10⁻¹² m² · s⁻¹ at 100°C. The apparent activation energy of diffusion, E_D, and the heat of dissolution, H_s, of water in the polymer have opposite values (respectively, +43 and −42 kJ · mol⁻¹). From this observation and a comparison of these data with water diffusion characteristics in other glassy polar polymers, it is hypothesized that the transport rate of water is kinetically controlled by the dissociation of water–polymer complexes. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1439–1444, 2000     

Dynamic adsorption behaviors between Cu2+ ion and water‐insoluble amphoteric starch in aqueous solutions

Dynamic adsorption behavior between Cu²⁺ ion and water‐insoluble amphoteric starch was investigated. The sorption process occurs in two stages: external mass transport occurs in the early stage and intraparticle diffusion occurs in the long‐term stage. The diffusion rate of Cu²⁺ ion in both stages is concentration dependent. In the external mass‐transport process, the diffusion coefficient (D₁) increases with increasing initial concentration in the low‐ (1 × 10^?3‐4 × 10^?3M) and high‐concentration regions (6 × 10^?3‐10 × 10^?3M). The values of adsorption activation energy (k_d1) in the low‐ and high‐concentration regions are 15.46–24.67 and ?1.80 to ?11.57 kJ/mol, respectively. In the intraparticle diffusion process, the diffusion coefficient (D₂) increases with increasing initial concentration in the low‐concentration region (1 × 10^?3‐2 × 10^?3M) and decreases with increasing initial concentration in the high‐concentration region (4 × 10^?3‐10 × 10^?3M). The k_d2 values in the low‐ and high‐concentration regions are 9.96–15.30 and ?15.53 to ?10.71 kJ/mol, respectively. These results indicate that the diffusion process is endothermic in the low‐concentration region and is exothermic in the high‐concentration region for both stages. The external mass‐transport process is more concentration dependent than the intraparticle diffusion process in the high‐concentration region, and the dependence of concentration for both processes is about equal in the low‐concentration region. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2849–2855, 2001     

Annular flow configuration with high deposition efficiency for the experimental determination of thermophoretic diffusion coefficients

An experimental study was carried out to produce reliable data for the determination of the thermophoretic diffusion coefficient K_th of suspended oil particles in air, in the transition regime. An original device was used for the thermophoretic deposition efficiency measurement, involving a turbulent flow through a concentric tube annulus, with the inner tube cooled (5 °C) and the outer heated. Experimental parameters varied in particle diameter (0.039–5.13 μm), flow rate (150, 200, and 250 Nl min⁻¹, corresponding to Reynolds number in the range 5000–10 000) and hot wall temperature (65–125 °C). This configuration, based on three controlled temperatures (gas inlet, cold wall, hot wall), the so-called “3T”, permits an overall deposition efficiency enhancement compared to conventional “2T” penetration devices (hot gas flow in a cooled tube). In the 3T configuration, significant thermophoretic deposition efficiencies have been obtained (up to 27%), together with limited gas temperature axial variations, thus permitting a reliable determination of the thermophoretic diffusion coefficient K_th.An analytical model was developed for the prediction of the thermophoretic deposition efficiency, for a given value of the thermophoretic diffusion coefficient K_th. This model has been used, together with our measurement results, to derive the K_th experimental values, for a Knudsen number ranging from 0.01 to 3. These K_th values were compared with evaluations based on various models available in the literature. Although widely used, Talbot's model always provides K_th values higher than our experimental results in the transition regime. The most relevant model appears to be the one proposed by Beresnev and Chernyak, particularly for an energy accommodation slightly lower than one.     

Sorption and diffusion of organic vapors in two fluoroelastomers

Immersion experiments with Aflas (I), poly(tetrafluoroethylene‐co‐propylene), and Fluorel (II) [poly(vinylidene fluoride‐co‐perfluoropropylene)], showed greater swelling of I in nonpolar liquids and much higher swelling of II in polar liquids: over 100% (wt/wt) in two ketones and a phosphate ester. Sorption isotherms determined for toluene and acetone at 25 and 35°C were fitted with the Flory–Rehner relation, employing a concentration‐dependent solvent–polymer interaction parameter. The fitted K parameters indicated that the degree of crosslinking in II was lower than in I. However, the high swelling of II by polar solvents is attributed primarily to the polar nature of II resulting from the asymmetric CF(CF₃) moiety. Diffusion coefficients determined from sorption kinetics, corrected for nonisothermal effects, and converted to solvent self‐diffusion coefficients were fitted with the Fujita free‐volume relation. The values were much higher for I than II with acetone and also slightly higher for I with toluene. The estimated zero‐concentration values were 1.5 E‐09 cm²/s for Aflas–acetone, 0.3 E‐09 cm²/s for Fluorel–acetone, and even lower for toluene. The low diffusion coefficients, which contribute to the superior barrier performance of these elastomers, is due, in part, to the high glass transition temperatures of I and II, −7 and −21°C, respectively. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1525–1535, 1999     

Transport of cadmium and iron through a carboxylic membrane based on a poly(vinyl chloride)/poly(methyl methacrylate‐co‐divinyl benzene) system

The transport of cadmium and iron through a poly(vinyl chloride)/poly(methyl methacrylate‐co‐divinyl benzene) carboxylic ion‐exchange membrane was investigated with a system containing HCl as the receiver solution and CdCl₂ or FeCl₃ as the feed solution. Transport of the ions through the membrane depended on the H⁺ concentration in the receiver solution and the metal concentration in the feed solution. The rate of transfer for cadmium was about 35% higher than that for iron under the same conditions (0.5 mol/dm³ of HCl, 0.1 mol/dm³ of CdCl₂ or FeCl₃, and 5 h of dialysis). © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 705–707, 2005     

Structural Origin of the Thermal and Diffusion Behaviors of Lithium Aluminosilicate Crystal Polymorphs and Glasses

Lithium aluminosilicate polymorphs α–LiAlSi₂O₆, β–LiAlSi₂O₆, and the LiAlSi₂O₆ glass have been studied comparatively using classical molecular dynamics (MD) simulations with an aim to better understand the structural origin of the different thermomechanical behaviors and lithium ion diffusion properties. The melting behaviors and structural evolution were investigated for the three phases using MD simulations. The structural features of the three simulated samples were analyzed using coordination number, pair and bond angle distributions. The results showed that β‐LiAlSi₂O₆ and the LiAlSi₂O₆ glass had similar melting behavior, had more random short‐range atomic structures, and lower densities as compared to the α‐LiAlSi₂O₆ phase, which has a more ordered and compact structure. The lithium ion diffusion behavior in α–LiAlSi₂O₆, β–LiAlSi₂O₆, and LiAlSi₂O₆ glass and their melts are determined and compared by calculating the mean square displacements. It was found that at high temperatures, the melts of α–LiAlSi₂O₆, β–LiAlSi₂O₆, and LiAlSi₂O₆ glass had similar diffusion properties. While at low temperatures, α–LiAlSi₂O₆ had the lowest diffusion coefficient and highest diffusion energy barrier due to its more close‐packed structure and lacking of defects to facilitate lithium ion diffusion. Both the β–LiAlSi₂O₆ and glass show high ionic conductivity even at low temperatures. This originates from their lower density and thus relatively open structures, but slightly different diffusion mechanisms. Lithium ion diffusion in β–LiAlSi₂O₆ is through the large available interstitial sites while that in the glass is through vacancies due to high free volume. The glass phase had slightly lower lithium ion diffusion energy barrier and higher lithium ion diffusion coefficients as compared to the β–LiAlSi₂O₆ phase, indicating the glass phase can achieve high ionic diffusion and, in some cases, even higher than the crystalline phases with similar densities and short‐range structures.     

Mechanism of Nanovoid Formation at the ZnO–Glass Interface in Planar Multilayered Structures of AlOx–ZnO–Glass

Functional porous materials require easy fabrication methods with controllability of a wide range of pore size and its density for practical applications including optical devices. The Kirkendall effect based on unbalanced material diffusion provides such a possibility in conjunction with material configurations of multilayers. This study reports a formation of nanoscale pores within ZnO films in planar multilayered structures of Al₂O₃–ZnO‐aluminosilicate glass and demonstrates the mechanism of forming relatively large nanopores in ZnO near the ZnO–glass interface via stress‐promoted Kirkendall diffusion. Experimental characterizations supported by atomic simulation reveal that an enhanced in‐plane tensile stress in the ZnO films with increasing the thickness of the neighboring Al₂O₃ films can promote the diffusivity of the Zn atoms and the pore growth in the ZnO films. The pore size and location in the intermediate ZnO layer of the Al₂O₃–ZnO–glass is alterable by simply selecting the thickness of the Al₂O₃ layer. Promoted diffusion of the Zn atoms enables to fabricate porous planar ZnO films with pore sizes up to a few hundred nm with an enhanced light scattering ability. These findings offer a promising route to produce porous planar films through in‐depth understanding of diffusivity enhancement in glass–metal oxide couples.     

Properties of aligned poly(L‐lactic acid) electrospun fibers

Poly(L‐lactic acid) (PLLA)‐aligned fibers with diameters in the nano‐ to micrometer size scale are successfully prepared using the electrospinning technique from two types of solutions, different material parameters and working conditions. The fiber quality is evaluated using scanning electron microscopy (SEM) to judge fiber diameter, diameter uniformity, orientation, and appearance of defects or beads. The smoothest fibers, most uniform in diameter and defect free, were found to be produced from 10% w/v chloroform/dimethylformamide solution using an accelerating voltage from 10–20 kV. Addition of 1.0% multiwalled carbon nanotubes (MWCNT) into the electrospinning solution decreases fiber diameter, improves diameter uniformity, and slightly increases molecular chain alignment. The fibers were cold crystallized at 120°C and compared with their as‐spun counterparts. The influences of the crystalline phase and/or MWCNT addition were examined using fiber shrinkage, temperature‐modulated calorimetry, X‐ray diffraction, and dynamic mechanical analysis. Crystallization increases the glass transition temperature, T_g, slightly, but decreases the overall fiber alignment through shrinkage‐induced buckling of the fibers when heated above T_g. MWCNT addition has little impact on T_g, but significantly increases the orientation of crystallites. MWCNT addition slightly reduces the dynamic modulus, whereas crystallization increases the modulus in both neat‐ and MWCNT‐containing fibers. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41779.     

Transport and solubility of fluids into polyphenylene sulfide (PPS)

The solubility and transport of toluene and carbon disulfide into amorphous and crystalline polyphenylene sulfide (PPS) was investigated. The rates of sorption, desorption, and resorption of both fluids were measured as a function of temperature. The sorption of these fluids into amorphous PPS produces a semi‐crystalline material by solvent induced crystallinity (SIC). Although the rate of diffusion of carbon disulfide (CS₂) into crystalline PPS, (produced either thermally or by SIC), is several orders of magnitude slower than that observed in amorphous PPS, the solubility is only slightly reduced, by approximately 10%. The PPS films exhibit highly stressed surface regions that rapidly sorb the penetrant. Thermal annealing at temperatures as high as 100°C (note T_g of PPS is 85°C) has little or no effect on the surface stress, the diffusion process or the solubility of toluene into PPS. In addition to SIC, PPS undergoes cold crystallization at 130°–140°C; however, the degree of crystallinity induced by cold crystallization is approximately 60% of that formed by cooling from the melt. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 615–625, 2003     

Interaction of crosslinked ethylene–propylene–diene terpolymer blends with chlorinated organic penetrants

The sorption and diffusion of halogenated hydrocarbon penetrants through different ethylene–propylene–diene terpolymer (EPDM) blends, such as EPDM/natural rubber, EPDM/bromobutyl rubber, and EPDM/styrene butadiene rubber (50/50 w/w), were studied. The diffusion coefficient of halogenated penetrants fell in the range 1.5–14.52 × 10^?7 cm²/s in the temperature range of 25–60°C. Transport data were affected by the nature of the interacting solvent molecule rather than its size and also by the structural variations of the EPDM blends. 1,2‐Dichloroethane showed a lower mass uptake compared to other penetrants. The temperature dependence of the transport coefficient was used to estimate the activation parameters, such as the activation energy of diffusion (E_D) and the activation energy of permeation (E_p) from Arrhenius plots. The activation parameters for E_D of aliphatic chlorinated organic penetrants was in the range 7.27–15.58 kJ/mol. These values fell in the expected range for rubbery polymers, well above their glass‐transition temperature. Also, the thermodynamic parameters, such as enthalpy and entropy, were calculated and fell in the range 2–15 kJ/mol and 3–54 J/mol/K, respectively. Both first‐ and second‐order transport kinetics models were used to investigate the transport kinetics, and first‐order kinetics were followed. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1366–1375, 2003     

Synthesis and characterization of salep sulfate and its utilization in preparation of heavy metal ion adsorbent

A multicomponent polysaccharide obtained from dried tubers of certain natural terrestrial orchids was chemically modified by sulfonation using chlorosulfonic acid–dimethylformamide (HClSO_3–DMF) complex as a reagent. For a structural characterization of salep sulfate ¹H nuclear magnetic resonance (NMR), Fourier transform infrared (FTIR) spectra, and Thermogravimetric analysis (TGA) curves were recorded. The sulfate content of modified salep was determined using elemental analysis. This modified biopolymer was used to prepare a new environment‐friendly heavy metal ion adsorbent, salep sulfate‐graft‐polyacrylic acid hydrogel (SS‐g‐PAA). Swelling rate and equilibrium water absorbency in various pH and saline solutions were investigated to study the effect of salep sulfate on swelling behavior of the hydrogel. In addition, the effect of sulfate content on heavy metal ion adsorption from aqueous solution was investigated. The results show that SS‐g‐PAA can effectively remove heavy metal ions (Co²⁺, Zn²⁺, Cu²⁺) from aqueous solution and swelling behavior of the hydrogels highly dependent on the amount of sulfate group on corresponding modified polysaccharide. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3001–3008, 2013     

Mathematical modeling of solid oxide fuel cells at high fuel utilization based on diffusion equivalent circuit model

Mass transfer and electrochemical phenomena in the membrane electrode assembly (MEA) are the core components for modeling of solid‐oxide fuel cell (SOFC). The general MEA model is simply governed with the Stefan‐Maxwell equation for multicomponent gas diffusion, Ohm's law for the charge transfer and the current‐overpotential equation for the polarization calculation. However, it has obvious discrepancy at high‐fuel utilization or high‐current density. An advanced MEA model is introduced based on the diffusion equivalent circuit model. The main purpose is to correct the real‐gas concentrations at the triple‐phase boundary by assuming that the resistance of surface diffusion is in series with that of the gaseous bulk diffusion. Thus, it can obtain good prediction of cell performance in a wide range by avoiding the decrement of effective gas diffusivity via unreasonable increment of the electrode tortuosity in the general MEA model. The mathematical model has been validated in the cases of H₂? H₂O, CO? CO₂ and H₂? CO fuel system. © 2009 American Institute of Chemical Engineers AIChE J, 2010     

Diffusion dynamics of ionic liquids during the coagulation of solution spinning for acrylic fibers

The coagulation dynamics of acrylic polymer (PAN) with 1‐butyl‐3‐methylimidazolium chloride [BMIM]Cl as solvent for PAN and H₂O as nonsolvent was investigated in detail. On the basis of Fick's second law of diffusion, a mass‐transfer model of [BMIM]Cl from concentrated PAN/[BMIM]Cl solution was established as verified with the experimental data. The established model has a good fit with the experimental data and the diffusion coefficient D of [BMIM]Cl was calculated according to the model. The diffusion coefficient D decreased a little when the concentration of solution increased. As increasing the coagulation bath concentration, the diffusion coefficient D initially increased and then decreased, reaching a maximum of 5 wt% in the coagulation bath. The diffusion coefficient D decreased with the coagulation bath temperature. From the diffusion coefficient and the structure of the coagulated filament, it can be concluded that the diffusion rate of [BMIM]Cl from PAN concentrate solutions is relatively slow, which is prospective to prepare uniform‐structure fibers. POLYM. ENG. SCI., 48:184–190, 2008. © 2007 Society of Plastics Engineers     

New evidence derived from the discrimination of Henry and Langmuir modes parameters in glassy polymeric film revealed by the Freeze‐Purged‐Desorption method

The Freeze‐Purged‐Desorption (FPD) method was developed for the experimental measurement of gas permeability coefficients as a new technique using a desorption curve of gas immobilized in polymeric films. The FPD method was effectively used to evaluate four gas permeation parameters (C_D, C_H, D_D, and D_H) of glassy polymeric films (polycarbonate and polystyrene) by using CO_2. The modes of the CO₂ gas desorption response curve (D‐curve) obtained were sensitively characterized by the proportion of sorption in the Henry and Langmuir modes in the polymeric films accompanied by their own gas diffusivity. A graphical analysis of the D‐curve of CO₂ reasonably proposed a linear relation between the desorption rate and the sorption amount of CO_2, which was strongly influenced by the kind of sorption gas, film, temperature, and other factors. The desorption rate of sorbed CO₂ gas for the PC and PS films gave a characteristic straight line with an inflection point indicating a shift in the gas‐diffusion mechanism from the complex type of the Henry and the Langmuir modes to the Langmuir mode. The characteristic D‐curves obtained were graphically analyzed, and they clearly discriminated the Henry mode part and the Langmuir mode part. This discrimination process quantitatively and individually evaluated C_D, C_H, D_D, and D_H. By using the four parameters evaluated, a mathematical model to describe the D‐curve was proposed, and it consistently explained the experimental D‐curves. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 934–941, 2004