Showing papers on "Permeation published in 1980"

17. Permeation, Diffusion, and Sorption of Gases and Vapors

Abstract: Publisher Summary This chapter describes the permeation, diffusion, and sorption of gases and vapors. The principal alternative to permeation rate measurements for transport coefficient determinations is the direct measurement of the rate of uptake or loss of a penetrant by a polymer sample. The advantages of the sorption approach are that it eliminates the need for elaborate sealing and the extreme leak sensitivity associated with permeation methods. It reduces uncertainties in the sample surface area caused by membrane supports, and it is well-suited to lengthy experiments on materials in which diffusion coefficients are low. In some instances, the determination of the extent of penetration may be performed by visual inspection, as when the penetrant advances in a well-defined front and swells or crazes the sample. A model that provides a consistently accurate representation of the permeation of gases above their critical temperatures, at atmospheric and subatmospheric pressures, through non-swollen rubbery polymers that do not contain crystallites or fillers is presented. The correlation and estimation of transport and solubility coefficients are also elaborated.

Water permeability of oil layers in W/O/W emulsions under osmotic pressure gradients

Abstract: Water permeability of oil layers in a series of water/hydrocarbon/water emulsions has been studied microscopically by measuring the rate of change in the size of the dispersed globules. A range of values, from 2 × 10−4 to 8 × 10−4 cm sec−1, has been obtained for the water permeation coefficient calculated by measuring the water flux occurring when various concentration gradients of glucose exist across the oil layer. The permeation coefficients scattered within the above range due to variations in the samples, such as oil layers made of different hydrocarbon preparations, different concentrations of the lipophilic emulsifying agent (Span 80), and various magnitudes of the osmotic pressure gradient between the aqueous dispersed compartments and the aqueous suspending medium. After comparing the permeation coefficient obtained in this study with those of lipid membrane systems, it seems that the oil layers in the W/O/W emulsions may be composed of multilamellar layers of the lipophilic emulsifying agent used for the emulsion preparation.

Content and Fluxes of Electrolytes

Abstract: The sections in this article are: 1 Physicochemical Models of Cellular Behavior 1.1 Prevailing Assumptions 1.2 Osmotic Properties 1.3 Membrane Diffusion 1.4 Electrochemical Potentials 2 Experimental Approaches 2.1 Chemical Dissection 2.2 Isotope Flux Analyses 2.3 Electron Probe Analyses 3 Ionic Transport Mechanisms 3.1 Simple Diffusion or Permeation 3.2 Active Transport 3.3 Exchange Diffusion 4 Control of Cellular H2O 4.1 Osmotic Balance 4.2 Transport Mechanisms 5 Temperature Dependence 5.1 Activation Energy 5.2 Phase Transitions 6 Effects of Excitatory Agents 6.1 Membrane Potentials 6.2 Ionic Fluxes 7 Divalent Ions 7.1 Calcium 7.2 Magnesium 8 Conclusion

Permeation measurements of hydrogen trapping in 1045 steel

Abstract: This work examined the role of microstructure in hydrogen permeation and trapping in a plain carbon steel. The experimental material, SAE 1045 steel, was characterized both as to microstructure and as to permeation behavior; these data can be used in interpreting hydrogen fracture observations. The gas-phase permeation results show that hydrogen is markedly trapped in this steel, apparently at ferrite-carbide interfaces. This suggests that the trapped hydrogen could facilitate crack initiation and crack propagation at these regions of high hydrogen concentration. The hydrogen traps are quite reversible, so that hydrogen can be put in and taken out quite readily. The trapping energy ranged from 4.4 to 8.7 kcal/mol, with a mean value of 6.4 kcal/mol (26.8 kj/mol), in agreement with previous studies.

Sorption and transport of water vapor in glassy poly(acrylonitrile)

Abstract: : Sorption data for H2O in glassy polyacrylonitrile (PAN) are presented for a range of relative vapor pressures at temperatures from 20C to 50C. Simple dual mode sorption, involving 'hole-filling' and molecular solution appears to dominate the low activity region of sorption. Based on the clustering analysis suggested by Zimm and Lundberg, pronounced clustering of penetrant appears to occur above a relative pressure of 0.6. The form of the effective concentration-dependent diffusion coefficient for H2O in PAN, determined by analysis of steady state permeation data, suggests that water in the microvoids and clusters has a lower mobility than the molecularly dissolved water in the polymer matrix. Time lag measurements at high upstream realtive water vapor pressures suggest that the transient state permeation has a non-Fickian character due to relaxations which occur slowly to accommodate the clustering process. (Author)

Selective permeation of hydrocarbon gases in poly(tetrafluoroethylene) and poly(fluoroethylene–propylene) copolymer

Abstract: The permeabilities and diffusivities of methane, ethane, propane, n-butane, and isobutane in commercially available poly(tetrafluoroethylene) (TFE) and poly(fluoroethylene–propylene) (FEP) Teflon have been measured in a Pasternak-type permeation cell. Experiments were carried out at upstream hydrocarbon partial pressures up to 50 torr (1000–60,000 ppm gas phase concentration) and temperatures from 40 to 195°C with films of 0.0508 and 0.127 mm thickness using nitrogen as carrier gas on the upstream and downstream sides of the membrane. The transient and steady-state permeation data are described well by a combination of Henry's law and Fick's law with a concentration-independent diffusion coefficient. Linear Arrhenius plots of both permeabilities and diffusivities were obtained. Linear correlations were found both between the activation energy for diffusion and the square of the gas molecule diameter, and between the logarithm of solubility at 90°C and the penetrant boiling point. Separation factors for binary mixtures of hydrocarbons were measured for TFE at 140°C and found to be similar to those predicted by individual permeabilities in most cases. Measurements with mixed gases were not made for FEP Teflon, but selectivities of FEP are expected to be similarly well described by the ratios of the pure gas permeabilities at the low partial pressures studied. The effect of annealing FEP Teflon for 24 hr at 200°C was found to produce an average of 20–30% reduction in solubility as well as a 9% increase in the activation energy for diffusion compared to as-received films. These effects are believed to be due to increased crystallinity in the sample upon annealing.

Fickian diffusion of alkanes through glassy polymers: Effects of temperature, diffusant size, and polymer structure

Abstract: Diffusivities D ranging over six orders of magnitude with values as low as 2 × 10−13 cm2/s have been obtained by a recently developed permeation apparatus, employing a gas-flow method and a flame ionization detector; Log D for hydrocarbons in bisphenol-A polycarbonate (PC) at 120°C is proportional to the square of the molecular diameter (d2) as given by the Lennard-Jones 6–12 potential. This correlation holds even for the nonspherical n-hexane molecule. The activation energy for diffusion is also linearly related to d2, with values of 9.5 and 23 kcal/mol for methane and neopentane in PC, respectively. Comparison of PC with two similar polymers of higher glass-transition temperatures (Tg) indicates that our diffusion data do not correlate with the Tg of these polymers. The presence of subsidiary transitions, however, appears to enhance segmental mobilities, increasing the rate of diffusion of the hydrocarbons. The thermodynamic solubility of alkanes in glassy PC can be directly related to their boiling points, and in addition, their enthalpy of solution is linearly related to the heat of condensation of these permeants.

High-Performance Gel Permeation Chromatography of Pectins

Abstract: A high-performance gel permeation chromatographic (GPC) method was developed to determine the molecular weight distribution of pectins. The chromatographic system consisted of a hydrophilic coated silica (SynChropak) as the packing and a pH 3.7 acetate buffer as the mobile phase. By use of this system, high-methoxy, low-methoxy, and amidated pectins could be analyzed within fifteen minutes. By determining partition coefficients (Kd) of pectins as a function of mobile phase composition, Kd values were found to be independent of ionic strength from 0.055 to 0.7 M using pH 3.7 acetate buffers, which was in agreement, with intrinsic viscosity data.

Mechanism of sulphur transport through preformed oxide scales

Abstract: The possibilities for transport of sulfur through preformed oxide scales by both solution-diffusion and molecular gas (24) permeation mechanisms are examined thermodynamically to establish the limiting conditions under which each is viable. The results are tested, using nickel and cobalt specimens, and it is concluded that, although both mechanisms may operate in parallel, the permeation of gas molecules is the more dangerous since it can operate over wider ranges of gas atmosphere composition. The permeation of SO2 molecules throu through oxide scales growing on cobalt is clearly demonstrated.

Permeability of oxygen through polymers. II. The effect of humidity and film thickness on the permeation and diffusion coefficients

Abstract: The values of the permeability coefficient P (cm2/sec) and the diffusion coefficient D (cm2/sec), of oxygen in some water-soluble polymers at various values of relative humidity were determined. The amount of oxygen initially present in the polymer membranes was calculated. The effect of sample preparation and the film thickness on the transport parameters was investigated. The results confirm the possible effect of thickness on the rate of transport of oxygen in water-soluble polymers.

Vapor permeation curable coatings based on alkyd resins

Abstract: Improved coating compositions for use in diversified applications, curable by permeation of a tertiary amine vapor or without permeation at room temperature. The composition and the coating process are characterized by the modification of an alkyd resin, having free hydroxyl groups, by reaction with p-hydroxybenzoic acid. The coatings display good flexibility and high gloss as well as good color retention and good adhesion to substrates.

Mechanism of chloride ion transport through diaphragm-type liquid membrane

Abstract: The permeation mechanism has been studied to obtain fundamental information for developing liquid membrane process. Chloride ion was concentrated across a diaphragm-type liquid membrane impregnated with Amberlite LA-II as a mobile carrier. This process is considered to constitute a kind of active transport process. The permeation rates of chloride ion are explained approximately by a permeation model in which hydrochloric acid reacts with the carrier at the interface of one side of the membrane and the complex formed by the reaction then diffuses through the membrane and further reacts with sodium hydroxide in the vicinity of the opposite interface.

Creatine transport into red blood cells

Abstract: The permeation of creatine from plasma into normal human red blood cells was investigated by means of 1-[14C]-creatine. Two statistically different Vmax and Km values were found for lower and for higher creatine concentrations of the plasma, respectively, indicating two types of transport with different affinities and capacities. It is suggested that the high affinity process, which accounts for 1/4 of the capacity and has an affinity constant of 0.087 +/- 0.032 mM is an active transport, while the low affinity transport represents an exchange diffusion. There is little, if any, effect of pH in the range of 6.9-7.9 on the transport. The total creatine concentration of the red cells did not change significantly even with high creatine concentration of the plasma during 6 h incubation at 37 degrees C. The in vitro experiments showed a daily exchange of cellular creatine of 20%, the t0.5 being about 2.5 days.

Permeation barrier for display cells

Abstract: Cells, such as liquid crystal display cells, having a material contained between a pair of parallel, spaced-apart substrates, are sealed to prevent permeation therein of vapor which is potentially harmful to the material contained within the cell, by reducing the area of relatively high permeation material at the cell boundary and/or by completely enclosing the boundary in a permeation resistant barrier of inorganic material.