Corinne Chappey

water vapor sorption in naphthalenic sulfonated polyimide membranes

Abstract The water vapor uptake of sulfonated polyimides (SP) was investigated by electronic microbalance (IGA, Hiden) from 15 to 55°C. The sigmoidal isotherms obtained (BET II type) are considered as dual sorption (concave part) plus clustering (convex part) and are fitted with good agreement by Park’s equation. Zimm–Lundberg’s method is used to study the clustering process of water molecules: limit clustering activity, a ∗ , and the number of molecules per cluster are estimated. To obtain a better understanding of polymer structure and isotherm analysis, H + (counter-ions of sulfonic groups) were replaced by ions with a smaller hydration shell (Cs + and EDAH + ). Comparison of the three isotherms shows no significant difference in the water affinity of the cations. This is attributed to a partial control of the sorption by microcavities existing in the membrane.

Residual solvent effect on the permeation properties of fluorinated polyimide films

The main aim of this study was to determine how the residual solvent remaining after fabrication affected the gas permeation properties of 6FDA–mPDA polyimide films. For this purpose, films were made by spreading solutions of polyimide from different solvents on glass plates, then treated at 200°C for different periods of time. The films obtained were characterized by differential scanning calorimetry, thermogravimetry and permeametry. Permeation parameters (D, P, S) of the films towards N2 and CO2 were determined at 35°C. They were found to be dependent on the residual solvent in the films. Whatever the solvent, the difference in behaviour was found to decrease as the amount of solvent became smaller and to increase with the molar volume of the solvent. Solvents with high molar volumes left an imprint in the material during thermal treatment.

Polyepichlorhydrin Membranes for Alkaline Fuel Cells: Sorption and Conduction Properties

Polymer electrolytes, using a poly(epichlorhydrin-allyl glycidyl ether) copolymer as matrix, are shown to perform well in alkaline fuel cell electrolyte. An anion-conducting network is obtained by the incorporation of cyclic diamines, 1,4-diazabicyclo[2.2.2]octane (DABCO) and 1-azabicyclo[2.2.2]octane (quinuclidine). The physicochemical and electrochemical characteristics are evaluated. The best conductivity of 1.3.10 (-2) S/cm is obtained at 60 degrees C and a relative humidity of RH = 98%. Ionic conductivity is particularly sensitive to relative humidity. To gain insight into the OH (-) conduction mechanism and the role of water, sorption measurements versus water activity, differential scanning calorimetry, and NMR measurements are carried out.

Kinetics of water vapor sorption in sulfonated polyimide membranes

Abstract Water vapour sorption kinetics in a H+ form naphtalenic sulfonated polyimide membrane at 25°C has been investigated by using an electronic microbalance (IGA, Hiden). An effective diffusion coefficient Dexp has been calculated from kinetic data by using the Fickian model for the final part of the sorption. The variation of Dexp with the equilibrium water activity (0

Facilitated transport of boric acid by 1,3-diols through supported liquid membranes

Boric acid is selectively transported by 1,3-diols from a source aqueous phase into a receiving alkaline aqueous phase through a phase of organic solvent (o-dichlorobenzene). Measurements of the transport rates were made using a U-tube apparatus. The process was adapted to liquid membranes supported on polypropylene films. The factors which influence the stability of the supported liquid membrane are discussed. Assuming that the transport of the neutral 1:1 diol-boric acid complex within the organic phase is diffusion-limited, a model is proposed that realistically represents the fluxes of boric acid as a function of the initial concentrations of boric acid and diol. The experimental diffusion coefficients were determined and agreed satisfactorily with the calculated values.

Transport Mechanisms of Small Molecules through Polyamide 12/Montmorillonite Nanocomposites

The aim of this work is to study the transport of small molecules through the hybrid systems polyamide 12 (PA12)/organo-modified montmorillonite (Cloisite 30B, C30B) prepared by melt blending, using two blending conditions. The transport mechanisms were investigated by using three probe molecules: nitrogen, water, and toluene. While a barrier effect appears clearly with nitrogen, this effect changes with the amount of fillers for water and disappears for toluene. The reduction of permeability for nitrogen is mainly due to the increase of tortuosity. For water and toluene, the permeation kinetics reveals many concomitant phenomena responsible for the permeation behavior. Despite the tortuosity effect, the toluene permeability of nanocomposites increases with C30B fraction. The water and toluene molecules interact differently with fillers according to their hydrophilic/hydrophobic character. Moreover, the plasticization effect of water and toluene in the matrix, involving a concentration-dependent diffusion coefficient, is correctly described by the law D = D(0)e(gammaC). On the basis of Nielsens tortuosity concept, we suggest a new approach for relative permeability modeling, not only based on the geometrical parameters (aspect ratio, orientation, recovery) but also including phenomenological parameters deduced from structural characterization and permeation kinetics.

Influence of solvent and non-solvent on polyimide asymmetric membranes formation in relation to gas permeation

Abstract Asymmetric 2,2-bis (3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA)-2-methyl-1, 3-phenylenediamine (mPDA) polyimide membranes were prepared by phase inversion process. Using different non-solvents and solvents, the correlation between membrane elaboration conditions and final morphology and properties has been investigated. Equilibrium thermodynamics and diffusion coefficients data were determined as a preliminary analysis in order to underline competitivity between thermodynamic and kinetic parameters. Scanning electron microscopy and gas permeation experiments (CO 2 , N 2 ) were used for the determination of structure-permeability relationships. Sponge-like structure membranes and highest selectivity were obtained when using non-solvent/solvent/6FDA-mPDA systems having important coagulation time.

Permeation Properties of Poly(m-xylene adipamide) Membranes

The permeation properties of a semiaromatic polyamide, the poly(m-xylene adipamide) (MXD6), were investigated by water and carbon dioxide permeation experiments (pervaporation and gas permeation tests). Complementary microstructure informations were obtained from calorimetric measurements. Amorphous and semicrystalline MXD6 membranes were studied. The analysis of the water flux through amorphous MXD6 membranes showed a plasticization phenomenon followed by a water-induced crystallization. It resulted that the role played by water in these materials was complex because of the dependence of the water diffusivity on water concentration and time. Because of the presence of crystalline phase, a significant reduction of water and gas permeability of MXD6 and an increase in the delay of diffusion were observed. In terms of barrier properties for water and carbon dioxyde, MXD6 membrane crystallized at high temperature were more performant than water-induced crystallized ones. Correlations between microstructure and transport properties had been so established.

Effect of cold plasma treatment on surface properties and gas permeability of polyimide films

The surface functionalization of polyimide (Matrimid® 5218) films was carried out by cold plasma treatment with CF4, N2 and O2 gases using a radio frequency discharge and the optimum plasma conditions were evaluated by water contact angle measurements. The surface hydrophobicity of polyimide films was obtained after CF4 plasma treatment, while O2 and N2 plasma treatments contributed to the hydrophilic surface functionalization. X-ray photoelectron spectroscopy (XPS) results revealed the presence of CFx, amino or oxygen-containing groups attached to the polyimide film surface depending on the treatment gas. A strong influence of the used plasma gas on the film roughness was determined by atomic force microscopy (AFM) measurements. The influence of the surface modification on CO2, N2 and O2 gas permeation through the plasma treated films was evaluated. The permeation behaviour was characterized in terms of transport parameters, namely, coefficients of permeability, diffusion and solubility. The permeability coefficient of all plasma treated polyimide films for the studied gases (CO2, N2 and O2) was found to decrease following the order of increasing the kinetic molecular diameter of the penetrant gas. Besides, the selectivity coefficient was found to be significantly increased after the plasma treatments – αCO2/N2 was increased up to 36% and 98% for O2 and N2 plasma treated Matrimid® 5218 films, respectively. The relationship between the gas permeation behaviour and the surface modification of polymer film by cold plasma was discussed.

Ab initio study of cationic polymeric membranes in water and methanol

The work is devoted to a computational study of three types of cationic polymeric membranes in Li+-ionic form, in water and methanol environments, at various solvation levels. The studied membranes Nafion, IonClad, and M3 possess the perfluorinated backbone; however, various side chains were terminated with the functional groups of distinctly different ionic strength. The paper discusses the structural features of the membrane-solvent clusters as well as an influence of the side chain nature on the dissociation of the functional groups and the binding energy of the solvent molecules. Additionally, the paper compares the obtained results for Li+-Nafion membrane in water with the results published earlier for H+ and Na+ forms.