摘要:

The transport of dissolved oxygen in water through a silicone rubber membrane was studied theoretically and experimentally. The apparent oxygen permeability coefficients of silicone rubber were measured at various membrane thicknesses, temperatures, and concentration levels. The permeation flux was measured under both steady-and unsteady-state conditions. For the first time, the thickness effect of dissolved gas permeation has been studied. It was found that the apparent permeability increases with increasing membrane thickness and approaches asymptotically to the gas phase permeability. A general equation was developed to explain this phenomenon based on the concept of immobile boundary layers. It was also observed that the apparent oxygen permeability increased exponentially with increasing concentration levels in water. The temperature dependency of permeability was of the Arrhenius type.

ISSN:0022-2348    

DOI:10.1080/00222347108212517

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

The diffusive transport of several simple gases in four thermoplastic elastomers was measured. Certain anomalies were observed with the larger-sized penetrants, namely Ar and N2. It appears that these gaseous penetrants can distinguish between the rigid and flexible regions of certain block copolymers, the effect being more pronounced for the gas with the larger molecular diameter. A model is proposed and discussed which is qualitatively consistent with the observed behavior.

ISSN:0022-2348    

DOI:10.1080/00222347108212518

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

The permeability, diffusivity, and solubility of He, Ne, Ar, and Kr were determined in poly(methyl acrylate) (PMA), in a temperature range encompassing the glass transition temperature, Tg. Activation energies for diffusion, ED, were higher above Tg than below Tg for all four penetrants in PMA and in the structural isomer of PMA, poly(vinyl acetate) (PVA). For all penetrants studied, the Tg, the magnitude of the enthalpy of mixing (ΔHm), as well as the EDwere all larger for PVA than for PMA. These differences were attributed to the stronger dipole-dipole interactions possible in PVA where the dipolar carbonyl group is separated from the chain backbone by an oxygen atom.

ISSN:0022-2348    

DOI:10.1080/00222347108212519

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

The permeation of He, N2, CH4, C2H6, C2H4, CO2, and N2O through polyethylene membranes has been studied at pressures up to 60 atm and at temperatures between −10° and 60° C. The experimental temperature range encompassed the critical temperature of the last four penetrants. The mean permeability coefficient,P, for C2H6, C2H4, CO2, and N2O exhibited an exponential dependence on pressure at reduced penetrant temperatures below and near unity. This dependence decreased with increasing reduced temperature. The values ofPfor CH4, which were obtained at reduced temperatures above unity, were essentially constant over the entire pressure range. Finally, theP's for N2and He, which were measured at the highest reduced temperatures, appeared to decrease slightly with increasing pressure. Possible causes for the observed behavior are discussed, and a new correlation for the pressure dependence of the permeability coefficients is presented.

ISSN:0022-2348    

DOI:10.1080/00222347108212520

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

A study has been made of the diffusion, solubility, and separation of nitrogen and methane gases at temperatures ranging from 15° to 50°C in a series of Teflon FEP copolymer films which were irradiated by γ rays in air and under vacuum. The irradiated films were subjected to postirradiation treatment temperatures above and below the glass I transition temperature of the copolymer. The effect of radiation on crystallinity and cross-linking was examined by density, thermal, and tensile strength measurements. Diffusion and permeability coefficients of both gases decreased with irradiation dose but solubility coefficients were not greatly affected. Nitrogen-methane separation factors for vacuum-irradiated films increased with irradiation dose, but little change was observed for the air-irradiated films. Chain scission appeared to be the predominant reaction in air-irradiated films whereas both cross-linking and chain scission occurred in vacuum-irradiated films depending on post-irradiation heat-treatment conditions. The permselectivity of the Teflon FEP films was increased by γ irradiation but this was achieved at the expense of the permeation rate.

ISSN:0022-2348    

DOI:10.1080/00222347108212521

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

A theoretical interpretation for the permeation of binary organic liquid mixtures through polymer films is developed. The model is based on an extension of the free-volume theory for diffusion of organic substances in polymers and takes into account the effect of one component of the mixture on the diffusion of the other component. The calculated permeabilities are in reasonable agreement with experimentally measured data.

ISSN:0022-2348    

DOI:10.1080/00222347108212522

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

The concept of a homogeneous polymer membrane, in which randomly coiled macromolecules pack the solid phase uniformly leaving some unoccupied space as free volume, has been applied in the study of permeability and selectivity of solutes through water (solvent)-swollen polymer membranes. Using this treatment, it became clear that fundamental principles of permeation through polymer film, i.e., a solution and diffusion mechanism of permeation, is also applicable to these swollen systems. However, the permeability characteristics of highly swollen systems resemble that of porous media due to the presence of the solvent, and the permeability of a swollen system to a solute cannot be characterized by a single permeability coefficient. The permeabilities based on diffusive flux (molecular flow) and on bulk flow of solvent, both of which occur under certain conditions, should be differentiated. Consequently permeability and permselectivity depend on the type of processes or conditions under which permeability is measured. Conformational entropies of macromolecules seem to play a predominantly important role in permselectivity and also in semipermeability (permselectivity between solute and solvent) of water-swollen membranes. Semipermeability depends on the combination of solute and solvent as well as on membrane characteristics such as swelling ratio. Membrane charge was found to have marked influence on permselectivities of ionized solutes. In general, the permselectivity decreases with increasing swelling ratio and consequent increasing permeability or flux of the solutes.

ISSN:0022-2348    

DOI:10.1080/00222347108212523

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

The ion-exchange selectivity parameters for the exchange of trace calcium, strontium, cobalt, nickel, zinc, and cadmium ions with hydrogen ion in cross-linked polystyrene-sulfonic acid cation exchangers have been determined from equilibrium ionic distribution measurements at 25°C in dilute solutions of perchloric acid and polystyrene-sulfonic acid. The selectivity behavior in perchloric acid solutions shows that the divalent ion is always preferred by the resin phase. The selectivity coefficients are a smooth function of resin phase concentration, increasing with concentration for Sr2+more than for Ca2+and Cd2+and being practically independent of resin phase concentration for Co2+, Ni2+, and Zn2+. The selectivity coefficients measured in salt-free solutions of polystyrene-sulfonic acid show a marked dependence on the polyelectrolyte concentration, the divalent ion being preferred by the aqueous phase. This preference diminishes with the concentration of polyelectrolyte. These results are interpreted by resort to the Gibbs-Duhem equation. This thermodynamic analysis has been facilitated by the availability of osmotic coefficient data for the pure polyelectrolyte ion forms over a large concentration range. Ion-exchange selectivity predictions by using this approach accurately reflect the observed ion-exchange selectivity behavior.

ISSN:0022-2348    

DOI:10.1080/00222347108212524

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

Electroosmotic transport of water accompanying ion transport across an anion-selective membrane has been measured at 25°C using 0.01 N NaC1 solution. Also electrical conductance, self-diffusion coefficient of counterion, and hydrodynamic permeability of the membrane have been measured. These data and others, such as water content and exchange capacity, have been used in the relations derived by Scattergood and Lightfoot employing the generalized Stefan-Maxwell equations to obtain values for the diffusivity coefficientsD1*1,D13,D14, and D34.The isotope interaction termD1*1was the lowest.

ISSN:0022-2348    

DOI:10.1080/00222347108212525

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

The permeability of cellulose 2.5-acetate films to several electrolytes and nonelectrolytes was measured. Permeabilities were determined by a desorption-rate method in which diffusion and distribution coefficients were measured. The rejection of the same solutes by modified cellulose acetate membranes in reverse osmosis experiments was also measured. A comparison was made between intrinsic water and solute permeabilities and the reverse osmosis semipermeability data using a noncoupled flow model of solute and water transport. The results were in reasonable agreement, indicating that flow coupling is not generally important in these films. Some of the factors, such as thermal history and casting environment, affecting the transport properties of acetone-cast cellulose acetate films were examined.

ISSN:0022-2348    

DOI:10.1080/00222347108212526

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor