Permeation of CO₂ and N₂ through glassy poly(dimethyl phenylene) oxide under steady- and presteady-state conditions

Glassy polymers are often used for gas separations because of their high selectivity. Although the dual‐mode permeation model correctly fits their sorption and permeation isotherms, its physical interpretation is disputed, and it does not describe permeation far from steady state, a condition expected when separations involve intermittent renewable energy sources. To develop a more comprehensive permeation model, we combine experiment, molecular dynamics, and multiscale reaction–diffusion modeling to characterize the time‐dependent permeation of N₂ and CO₂ through a glassy poly(dimethyl phenylene oxide) membrane, a model system. Simulations of experimental time‐dependent permeation data for both gases in the presteady‐state and steady‐state regimes show that both single‐ and dual‐mode reaction–diffusion models reproduce the experimental observations, and that sorbed gas concentrations lag the external pressure rise. The results point to environment‐sensitive diffusion coefficients as a vital characteristic of transport in glassy polymers

Permeation of CO2 and N2 through glassy poly(dimethyl phenylene) oxide under steady- and presteady-state conditions

Glassy polymers are often used for gas separations because of their high selectivity. Although the dual-mode permeation model correctly fits their sorption and permeation isotherms, its physical interpretation is disputed, and it does not describe permeation far from steady state, a condition expected when separations involve intermittent renewable energy sources. To develop a more comprehensive permeation model, we combine experiment, molecular dynamics, and multiscale reaction–diffusion modeling to characterize the time-dependent permeation of N2 and CO2 through a glassy poly(dimethyl phenylene oxide) membrane, a model system. Simulations of experimental time-dependent permeation data for both gases in the presteady-state and steady-state regimes show that both single- and dual-mode reaction–diffusion models reproduce the experimental observations, and that sorbed gas concentrations lag the external pressure rise. The results point to environment-sensitive diffusion coefficients as a vital characteristic of transport in glassy polymers

Strategies for studying permeation at voltage-gated ion channels

Voltage-dependent ion channels are presently thought to consist of several distinct functional regions: (a) activation gates, (b) inactivation gates, and permeation pathways. This chapter focuses on permeation pathways and may spur new ideas about experiments that use site-directed mutagenesis to probe the ion conduction pathway. Some hubris is required to attempt a survey of this field since individual families -- K^+, Na^+, or Ca^(2+) -- have been reviewed in detail (15, 68, 115, 127). My unified treatment is motivated by the structural similarity suggested by recent cDNA sequencing data on this group (see, for instance, 24). There have been many excellent previous treatments of ion channel permeation (6, 15, 34, 35, 51, 53, 68, 73, 74, 115, 127)

Gas separation properties of a thermally stable and chemically resistant polytriazole membrane

The polymer poly (1,3-phenyl-1,4-phenyl)-4-phenyl-1,3,4-triazole has been investigated for its gas separation properties. This thermally stable and chemically resistant polymer can be processed into membranes by the phase-inversion technique because of its unexpectedly good solubility in formic acid. Homogeneous membranes have been tested with respect to their permeability for several gases, and the influence of time and temperature upon permeation has been investigated. The polymer shows reasonable permeabilities for several gases and excellent selectivities. After a conditioning time of several days in which the permeability of the faster-moving gases increases by a factor of about 2, the permeation properties of the polymer remain constant for at least two months. A thermal treatment at 295°C, just above the glass transition temperature, can reduce the conditioning time and can prevent the film from shrinkage at high permeation temperatures without affecting the permeation properties

Financial permeation as a role of microfinance : has microfinance actually been helpful to the poor?

This article is distinct in its application of the logit transformation to the poverty ratio for the purpose of empirically examining whether the financial sector helps improve standards of living for low-income people. We propose the term financial permeation to describe how financial networks expand to spread money among the poor. We measure financial permeation by three indicators related to microfinance institutions (MFIs) and then examine its effect on poverty reduction at the macro level using panel data for 90 developing countries from 1995 to 2008. We find that financial permeation has a statistically significant and robust effect on decreasing the poverty ratio.Developing countries, Microfinance, Poverty, Poverty reduction, Financial permeation, Microfinance, Panel Data

Hydrogen transport in alpha titanium

Permeation experiments after nitriding the inlet surface of a hollow cylindrical membrane were conducted. Permeation data on two additional specimens given pre-oxidation or pre-nitriding treatments at both inlet and outlet surfaces are presented in terms of Arrhenius plots. Additionally, an analysis of geometry dependence on permeation rate was made for several specimens including the ones mentioned above. For simplicity in this report, the term as-polished is used to refer to a specimen which is either as-polished or is as-polished, pre-oxidized and annealed

Intermittent permeation of cylindrical nanopores by water

Molecular Dynamics simulations of water molecules in nanometre sized cylindrical channels connecting two reservoirs show that the permeation of water is very sensitive to the channel radius and to electric polarization of the embedding material. At threshold, the permeation is {\emph{intermittent}} on a nanosecond timescale, and strongly enhanced by the presence of an ion inside the channel, providing a possible mechanism for gating. Confined water remains surprisingly fluid and bulk-like. Its behaviour differs strikingly from that of a reference Lennard-Jones fluid, which tends to contract into a highly layered structure inside the channel.Comment: 4 pages, 4 figure

Graphene Multi-Protonation: a Cooperative Mechanism for Proton Permeation

The interaction between protons and graphene is attracting a large interest due to recent experiments showing that these charged species permeate through the 2D material following a low barrier (~ 0.8 eV) activated process. A possible explanation involves the flipping of a chemisorbed proton (rotation of the C-H$^+$ bond from one to the other side of the carbon layer) and previous studies have found so far that the energy barriers (around 3.5 eV) are too high to explain the experimental findings. Contrarily to the previously adopted model assuming an isolated proton, in this work we consider protonated graphene at high local coverage and explore the role played by nearby chemisorbed protons in the permeation process. By means of density functional theory calculations exploiting large molecular prototypes for graphene it is found that, when various protons are adsorbed on the same carbon hexagonal ring, the permeation barrier can be reduced down to 1.0 eV. The related mechanism is described in detail and could shed a new light on the interpretation of the experimental observations for proton permeation through graphene.Comment: 16 pages, 5 figure