Showing papers on "Permeation published in 1978"

Transient and steady‐state permeation in poly(ethylene terephthlate) above and below the glass transition

Abstract: Transient and steady-state permeation data are reported for CO2 in semicrystalline poly(ethylene terephthalate) for temperatures ranging from 25 to 115°C over the pressure range from 1 to 20 atm. The pressure dependency of the time lag and permeability disappears completely above the glass transition of the polymer, and Fick's law with a concentration-independent diffusion coefficient applies. In the glassy state, a concentration-dependent diffusion coefficient is necessary to describe the data. The form of this concentration dependence is described well by the partial immobilization transport model that attributes a different mobility to each of the two populations of sorbed gas which exist in local equilibrium with each other in glassy polymers. The importance of reporting the pressure used in transport experiments involving glassy polymers is emphasized by comparing the difference in the activation energy of the apparent diffusivity calculated from the measured time lag at 1 and 20 atm. Also, the magnitude of the observed slope discontinuity at Tg in Arrhenius plots of these apparent diffusities is shown to be a function of the upstream pressure used in the experiment. The independently measured time lags are compared with the predicated values calculated from various transport models and found to be described best by the partial immobilization model.

Gas separation by permeation Part I. Calculation methods and parametric analysis

Abstract: Calculation methods for single- and multi-stage permeation of a multi-component mixture are presented. The use of the local permeate concentration in the formulation results in a relatively simple form of solution for the binary system in the cross-flow pattern. A parametric analysis of the permeation cascade is given. For a given permeability of the more permeable component, there exists a membrane selectivity which gives rise to a minimum membrane area requirement in the cascade. It is shown that the compression power requirement is dependent only on the operating pressure ratios, irrespective of actual pressure levels in each stage. A study on the effect of interstage mixing loss shows that the ideal cascade (with no interstage mixing loss) is not necessarily always the thermodynamically most efficient one; some non-ideal cascades may have higher efficiencies due to more effective permeation steps. Examples given relate to He/CH4 and O2/N2 separations.

Vapor permeation time-temperature indicator

Abstract: A time-temperature indicator (t-T indicator) is described which is useful for monitoring the shelf lives of various perishable articles. The device is constructed of a vapor-permeable barrier positioned between a vapor and an indicator, both housed in a vapor-impermeable container. The device is activated just prior to the monitoring period by providing vapor to the container, as for example, by rupturing a solvent-filled frangible reservoir. The indicator, upon contact with the vapor produces a visual color response, and the vapor is constrained to permeate through the vapor-permeable barrier before contacting the indicator, thus creating a characteristic induction period before a color response occurs. The time required for the color response to occur in the device is a function of the temperature and time. The induction period can be varied by the thickness and type of material of construction used for the vapor-permeable barrier, the nature of the vapor and the nature of the indicator employed.

Hydrogen and deuterium permeation in copper alloys, copper–gold brazing alloys, gold, and the in situ growth of stable oxide permeation barriers

Abstract: The deuterium permeation through several copper alloys has been measured over a temperature range of 550 to 830 K using the membrane technique. In some cases, the hydrogen permeability was also measured. The results were divided into three categories: common alloys, gold alloys, and stable oxide forming alloys. Common alloys which showed typical bulk metallic diffusion with litle change in the permeation activation energy as compared to copper (77 kJ/mol for D2) were: (additions are in weight percent) 5% Sn, 2.3% U, 0.15% Zr, 4% Sn+4% Pb+4% Zn, 3% Si, and 7% Al+2% Fe. Compared to copper, the D2 permeability at 573 K was reduced by factors of 2.0, 2.7, 4.5, 5.3, 5.9, and 7.0, respectively. A series of gold–copper alloys including pure gold, 80% Au, 50% Au, 49% Au, and 35% Au also showed typical bulk metallic diffusion with a trend of decreasing permeability (increasing activation energies for permeation) with increasing gold content. There were also pronounced inflections or shifts in the permeability at ∠370°C, or about the order–disorder transition for Cu3Au and CuAu, for the 80% and 50% alloys. Two alloys did not exhibit bulk metallic permeation behavior and the permeabiltiy was in fact controlled by surface oxide layers. It was found that a layer of beryllium oxide could be formed on Cu+2% Be and a layer of aluminum oxide could be formed on Cu+7% Al+2% Si. As compared to 0.25 mm‐thick copper, the deuterium permeability at 500°C was reduced by a factor of ∠250 for Cu–Be and ∠1000 for Cu–Al–Si. The activation energies for deuterium permeation were 98 kJ/mol and 132 kJ/mol, respectively. The mechanism for the oxide growth is the high‐temperature hydrogen reduction of nearby less stable oxides, simultaneous with oxidation of the active metal, Be or Al, by trace amounts of water in the hydrogen. Ion microprobe mass analysis identified the oxide layers as containing beryllium or aluminum but not containing copper. The trend of activation energies found lends support to a theoretical model that relates the activation energy for diffusion to the shear modulus of the host oxide and the molecular radius of the diffusing molecule.

Effects of epinephrine on branchial non-electrolyte permeability in rainbow trout.

Abstract: Using isolated heads perfused at constant pressure, at rates close to those occurring in vivo, the permeability of the gills of the trout Salmo gairdneri to a range of solutes was measured. Under epinephrine-free conditions, butanol and water showed similar high branchial permeability coefficients. Urea, inulin and dextrans (mol. wt 3000 and 20 000) were 7–12 times less permeant, and mannitol 60-70 times less permeant than water or butanol. Epinephrine, at 10(−6) M, greatly increased the permeability of the gills to the small hydrophilic molecules, water and urea, and to the lipophilic substance, butanol, but did not affect the penetration of the large hydrophilic solutes, mannitol, inulin and dextrans. In the presence of 10(−6) M propanolol, a beta-blocker, epinephrine had no effect on the permeation of any of the test substances except that the permeability to urea decreased somewhat. The results suggest that epinephrine increases the permeability of the membranes of the branchial cells but does not affect the permeation of substances that cross the gill walls by paracellular routes or via an intracellular ‘bulk-transport’ mechanism. Such an action would be expected to increase the branchial transfer of oxygen.

Effect of electrodeposited metals on the permeation of hydrogen through iron membranes

Abstract: The permeability of electrolytically charged hydrogen through annealed Ferrovac E iron membranes was found to decrease significantly upon coating the charging surface of iron with thin layers of either Pt, Cu or Ni (Watts or electroless). The absorption of hydrogen was delayed for a period which depends on the nature and the thicRness of the metallic coating. The results show that such coatings do not have to be thicR or even continuous to be effective, in which case a catalytic mechanism is proposed to explain the marRed reduction in hydrogen permeation through the iron. Experimental confirmation is presented of this catalytic mechanism and of the barrier mechanism which is operative in the presence of dense continuous coatings. It is also shown that a decrease in catalytic activity occurs with time (aging) and is pronounced in the presence of As3+ ion.

Permeation of water vapor through cellulose triacetate membranes in hollow fiber form

Abstract: A modification of the carrier gas method for measuring permeability of a hollow fiber to a vapor is described with particular application to water vapor permeation through asymmetric cellulose triacetate in hollow fiber from. Conventional methods are inadequate because the high flux of permeation vapor combined with its low pressure on the permeate side and the small diameter of the fiber lead to an excessive buildup of pressure in the permeate stream—in some cases so great as to render much of the fiber length ineffective. The method described in this paper involves the permeation from the outside to the inside of the fiber of a binary mixture consisting of the water vapor and a fairly highly permeable carrier (helium). There is a significant pressure drop along the fiber, but a theoretical treatment is presented to take this into account and to permit a determination of the vapor permeability. Experiments at 35°C over a range of water vapor pressures up to 1.7 cm Hg gave a water flux of 9 × 10−3 cc(S.T.P.)/cm2-sec-cm Hg, with an apparent slight decrease with increasing pressure. Over the same range of water vapor pressure the helium flux decreased from 2.3 × 10−4 to 1.85 × 10−4 cc(S.T.P.)/cm2-sec-cm Hg.

Factors Influencing the Percutaneous Absorption of Drugs

Abstract: The skin is the most readily accessible organ of the human body; only a fraction of a millimeter separates its surface from the underlying capillary network. Yet, skin protects superbly against damage by micro- and macro-molecular entities, as well as against uncontrolled loss of vital biological substances, by virtue of its astonishingly low permeability to such substances. We have reexamined and attempted to reconcile the barrier characteristics of skin in terms not only of its composition and microstructure, but also of present understanding of membrane permeability and permselectivity. The principal barrier to percutaneous transport is localized within the stratum corneum. We have developed a mathematical model of this tissue as a two-phase protein-lipid heterogeneous membrane, which correlates the permeability of the membrane to a specific penetrant with the water solubility of the penetrant and with its lipid-protein partition coefficient. We have also found that a simplistic model of the sorption process, which invokes the coexistence of dissolved and mobile sorbed molecules in equilibrium with site-bound and immobile molecules within the membrane, accurately correlates experimental sorption data and transient transport measurements. The interstitial lipid phase of the stratum corneum is the cause of the exceedingly low, apparent diffusivity of drugs (e.g. scopolamine) and, in this regard, acts as the principal permeation barrier, whereas the drug sorbed by the stratum corneum is localized predominantly within the protein phase of the tissue. We have also found that the effects of the permeation adjuvant, dimethyl sulfoxide, on skin permeability are entirely consistent with accepted sorption-diffusion models of membrane transport, when changes in penetrant activity with changes in solvent composition and tissue microstructure induced by osmotic shock are properly allowed for.

Hydrocarbon separation through a liquid water membrane: Modeling of permeation in an emulsion drop

Abstract: The mass transfer of hydrocarbons within an emulsion drop has been modeled. The selective behavior of the process is attributed to the controlling effect of the aqueous phase; calculations show that the presence of a very thin membrane of water separating the inner core of the hydrocarbon droplets from the surrounding solvent is sufficient to explain observed selectivities.

Ion Selectivity in Membrane Permeation

Abstract: A basic function of cell membranes is discrimination in their permeability to such closely related ions as Na+ and K+, Ca2+ and Mg2+, or Cl− and I−. This ionic discrimination underlies such basic cellular phenomena as the generation of resting potentials, action potentials, receptor potentials, transmitter release, active transport, and enzyme activation. The present chapter has two purposes: to compare the ion discrimination observed for the passive permeation of cell membranes with that induced in artificial lipid bilayer membranes by certain ion translocators*; and to examine the most salient theories and approaches toward determining the molecular origins of ionic discrimination in membrane transport.

Permeability of poly‐L‐methionine membrane and its oxidized membrane to water vapor

Abstract: The permeability of poly-L-methionine (PLM) membrane and its oxidized form to water vapor was studied. Permeability coefficients of the PLM membrane were large, of the order of 10−7 cm3 (S.T.P.)·cm/cm2·sec·cm Hg. The sorption and permeation behavior of the PLM membrane was hydrophobic. The oxidized membrane was prepared by treating one or both sides of the PLM membrane with an aqueous solution of hydrogen peroxide. The membrane oxidized from one side is probably not layered but has a gradient of composition from one surface to the other. The amounts of water sorbed by the modified membrane increased with increase in oxidation time. The permeability coefficients of water vapor through the modified membrane were of the order of 10−6 cm3 (S.T.P.)·cm/cm2·sec·cm Hg.

Water permeation and solute rejection behaviors of a novel hydrophilic polyamide membrane

Abstract: The poly(BOL) membrane prepared by “casting polymerization” exhibited an excellent fractional solute-rejection behavior in the aqueous solution, having a comparatively sharp boundary region at the molecular weight range of about 200 to 1400, together with an extremely high water permeability. These conspicuous behaviors, as well as a great capacity for water absorption, may result from some delicate arrangement of polar hydrophilic and nonpolar hydrophobic microdomains probably formed along and between the polymer chains.

Interaction of keratinous substrates with sodium lauryl sulfate.. II. permeation through stratum corneum

Abstract: Neonatal rat STRATUM CORNEUM was used as a model membrane to investigate PERMEATION through mammalian skin. Passage of materials through these membranes was determined by use of radiotagged compounds and by spectrophotometric analysis. The anionic surfactant SODIUM LAURYL SULFATE penetrates the stratum corneum even at low concentrations. The diffusion constant for this process is about 10 -o cm"/sec, compared to 10 -6 cm"/sec for free diffusion in water. This SURFACTANT is bound to the skin in large amounts, up to 50% by weight at high concentrations. Pretreatment of the membrane by a cationic cellulose polymer (which is itself strongly sorbed) greatly reduced the amount of surfactant which passed through the membrane.