孔雀石绿分子印迹膜的制备和渗透性

以0.45 μm混合纤维素酯微孔膜为支载膜,丙烯酰胺为功能单体,N, N'-亚甲基双丙烯酰胺为交联剂,通过原位聚合法制备得到孔雀石绿分子印迹膜,并研究了其对模板分子和类似物的渗透性能。以分子印迹膜作为渗透膜,单一渗透实验中,13 h后MG的渗透量达到0.118×10^-3 g/cm²,而相同时间内甲基紫、甲酚红和溴百里酚蓝的渗透量分别为0.064×10^-3、0.057×10^-3和0.044×10^-3 g/cm²,且在竞争渗透中孔雀石绿的渗透速率没有发生明显变化,而甲基紫的渗透速率却显著下降。实验表明,分子印迹膜对模板分子孔雀石绿表现出良好的渗透选择性,且在与类似物甲基紫的竞争渗透中具有优先渗透能力。     

Vapor permeation of ethanol-water mixtures using sodium alginate membranes with crosslinking gradient structure

For the vapor permeation of ethanol-water mixtures, two types of dense sodium alginate (SA) membranes have been prepared: a nascent SA membrane and crosslinked SA membranes with glutaraldehyde (GA). In the vapor permeation of the concentrated ethanol-water mixtures through the SA membranes, the effects of feed temperature, cell temperature and crosslinking density in the membrane were investigated on the membrane performance, and a comparison of vapor permeation process was made with pervaporation. SA membranes having different crosslinking gradients have been fabricated by exposing the nascent membrane to different GA content of reaction solutions. The extent of the gradient was controlled by the exposing time. The permeation performance of the membranes will be discussed with the extent of the gradient. An optimal crosslinking gradient was determined in terms of flux and membrane stability. The separation of ethanol-water mixtures through the membrane with the optimal crosslinking gradient was carried out by vapor permeation and the permeation performance will be discussed, and compared with pervaporation.     

Comparison of the separation of lactic acid and l-leucine by liquid emulsion membranes

A mass transfer model originally proposed for the permeation of zinc and l-phenylalanine was slightly modified and used for calculating the mass transfer resistances in lactic acid permeation (using the secondary amine Amberlite LA-2 as a carrier) and l-leucine permeation (using the quaternary ammoniumchloride Aliquat 336 as a carrier). The results show that under optimized conditions lactic acid permeation is controlled by the rate of reaction and that l-leucine permeation is controlled by the rate of reaction and the diffusion through the emulsion globule. The model results were compared with batch experiments separating lactic acid and l-leucine from real fermentation broths. The comparison shows that the separation rate is affected by co-transport of pH regulating agents and to a smaller extent by the co-transport of water.     

Calculation of skin permeability coefficient for ionized and unionized species of indomethacin.

The contribution of ionized and unionized species to the overall permeation of weak electrolytes through the skin was investigated to determine the effect of pH in the vehicle on the permeability of indomethacin (IDM), as a model drug, through hairless rat skin. The permeability of IDM through polydimethylsiloxane (silicone) and poly(2-hydroxyethyl methacrylate) (pHEMA) membranes which may reflect lipid and aqueous pathway, respectively, was also measured for comparison. As the pH in the vehicle increased, there was an exponential increase in the skin permeation rate of IDM. The permeation rate of IDM through the silicone membrane was constant independent of pH, whereas that through the pHEMA membrane increased with increasing pH, similar to the skin permeation. The permeability coefficients of ionized and unionized species through the skin estimated using the skin permeation rates and solubilities of IDM at various pHs were 1.50 x 10(-7) and 2.79 x 10(-5) cm/s, respectively. These results indicated that the permeation of ionized species greatly contributed to the total permeation of IDM at higher pH, and that the total permeation rate of IDM was determined by the permeation of unionized species at lower pH. These contributions depend on the pH and pKa values and the ratio of permeability coefficient of each species. It was also confirmed that the skin has at least two kinds of permeation pathways and these two species permeate through a different pathway.     

Thermogravimetric calibration of permeation tubes used for the preparation of gas standards for air pollution analysis

Sources of VOC (Volatile Organic Compounds) reference-materials at ppm and ppb levels are needed for calibration of air monitoring instruments. The permeation-tube technique is considered effective for the preparation of low concentration standards of high accuracy and stability. In this work, purpose-built PTFE permeation tubes, containing benzene, toluene, ethylbenzene, o-xylene or m-xylene (BTEX) were accurately and rapidly calibrated. Using the sensitive thermo-balance of a thermogravimetric apparatus, very low permeation rates were determined by the continuous monitoring of the tube weight loss as a function of time. Permeation rates in the range from 25 to 350 ng min(-1) were determined with precision. Thermogravimetry appears to be a rapid method for the measurement of weight loss at constant temperature, allowing rapid characterization and recalibration of permeation tubes. A detailed study on toluene, chosen as a typical case, showed that there are variations of the permeation rate in the long term. The temperature dependence of the permeation coefficient was also explored and permeation rates were shown to display an Arrhenius behavior in the temperature range 304-324 K. Thermodynamic parameters influencing the permeation were discussed.     

Comparison between the pervaporation and vapor permeation performances of polycarbonate membranes

The pervaporation and vapor permeation performance of symmetrical and asymmetrical polycarbonate membranes, prepared via a dry-phase inversion and wet-phase inversion methods, respectively, were studied by measuring the permeation rate and separation factor. It was found that the polymer concentration effect on the pervaporation performance for the symmetrical polycarbonate membrane was lower than that for the asymmetrical polycarbonate membrane. Compared with pervaporation, vapor permeation has a significantly increased separation factor with a decreased permeation rate for the symmetrical polycarbonate membrane. Water molecules preferentially dissolve into the symmetrical polycarbonate membrane and diffuse easily through the membrane.     

Permeation of particle through a four-helix-bundle model channel

By using molecular dynamics simulation, the dynamic behaviors of particle permeation through a four-helix-bundle model channel are studied. The interior cavity of the four-helix-bundle provides the "routes" for particle permeation. The main structural properties of the model channel are similar to those that appear in natural four-helix-bundle proteins. It is found that the interior structure of the model channel may greatly influence the permeation process. At the narrow necks of the model channel, the particle would be trapped during the permeation. There is a threshold value for the driving force. When the driving force is larger than this threshold value, the mean first permeation time decreases sharply and tends to be saturated. Increasing the temperature of either the model channel or the particle reservoir can also facilitate the permeation. Enhancing the interaction strength between the particle and monomer on the four-helix-bundle model chain will hinder the permeation. Hence, the electrical current which is induced by the particle permeation is a function of the driving force and temperature. It is found that this current increases monotonically as the strength of the driving force or the temperature increases, but decreases as the interaction strength between the particle and monomer increases. It is also found that the larger the friction coefficient, the slower the permeation is. In addition, the multiparticle (or multi-ion) permeation process is also studied. The permeation of multiparticle is usually quicker than that of the single particle. The permeation of particle through a five-helix-bundle shows similar properties as that through a four-helix-bundle.     

Membrane permeation of testosterone from either solutions, particle dispersions, or particle-stabilized emulsions

We derive a unified model that accounts for the variation in extent and rate of membrane permeation by a permeating species with the type of donor compartment formulation (aqueous and oil solutions, particle dispersions, and oil-in-water and water-in-oil emulsions stabilized by particles) initially containing the permeant. The model is also applicable to either closed-loop or open-flow configurations of the receiver compartment of the permeation cell. Predictions of the model are compared with measured extents and rates of permeation of testosterone across an 80 μm thick polydimethylsiloxane (PDMS) membrane from donor compartments initially containing testosterone dissolved in either aqueous or isopropylmyristate (IPM) solutions, aqueous or IPM dispersions of silica nanoparticles or IPM-in-water or water-in-IPM emulsions stabilized by silica nanoparticles. Using a single set of input parameters, the model successfully accounts for the wide variations in permeation behavior observed for the different donor formulation types with either closed-loop or open flow configurations of the permeation cell receiver compartment.     

A permeation theory for single-file ion channels: one- and two-step models

How many steps are required to model permeation through ion channels? This question is investigated by comparing one- and two-step models of permeation with experiment and MD simulation for the first time. In recent MD simulations, the observed permeation mechanism was identified as resembling a Hodgkin and Keynes knock-on mechanism with one voltage-dependent rate-determining step [Jensen et al., PNAS 107, 5833 (2010)]. These previously published simulation data are fitted to a one-step knock-on model that successfully explains the highly non-Ohmic current-voltage curve observed in the simulation. However, these predictions (and the simulations upon which they are based) are not representative of real channel behavior, which is typically Ohmic at low voltages. A two-step association/dissociation (A/D) model is then compared with experiment for the first time. This two-parameter model is shown to be remarkably consistent with previously published permeation experiments through the MaxiK potassium channel over a wide range of concentrations and positive voltages. The A/D model also provides a first-order explanation of permeation through the Shaker potassium channel, but it does not explain the asymmetry observed experimentally. To address this, a new asymmetric variant of the A/D model is developed using the present theoretical framework. It includes a third parameter that represents the value of the "permeation coordinate" (fractional electric potential energy) corresponding to the triply occupied state n of the channel. This asymmetric A/D model is fitted to published permeation data through the Shaker potassium channel at physiological concentrations, and it successfully predicts qualitative changes in the negative current-voltage data (including a transition to super-Ohmic behavior) based solely on a fit to positive-voltage data (that appear linear). The A/D model appears to be qualitatively consistent with a large group of published MD simulations, but no quantitative comparison has yet been made. The A/D model makes a network of predictions for how the elementary steps and the channel occupancy vary with both concentration and voltage. In addition, the proposed theoretical framework suggests a new way of plotting the energetics of the simulated system using a one-dimensional permeation coordinate that uses electric potential energy as a metric for the net fractional progress through the permeation mechanism. This approach has the potential to provide a quantitative connection between atomistic simulations and permeation experiments for the first time.     

Study on permeation behavior and chemical degradation of PA66 in acid solution

In many polymers under corrosive liquids, degradation followed after permeation of environmental solution for a long period. The permeation rate of environmental solution, in many cases, is very low in corrosion-resistant polymeric materials. Therefore, the observation of the permeation of environmental solution and degradation of polymeric materials are very difficult in practical application. A simulation of permeation of solution is required in order to understand the permeation behavior of environmental solution and polymer degradation. A detailed analysis of the permeation behavior of solution accompanied by chemical reaction is important to study for improving the lifetime of polymers. Polyamide 66 (PA66) and sulfuric acid solution were used to investigate the quantitative study of permeation of environmental solution and its relation to degradation of polymeric materials. Correlation between diffusion process and degradation of PA66 related to the decrease of weight average molecular weight was defined. The diffusion rate of sulfuric acid solution was found to increase by decreasing weight average molecular weight of PA66 due to the established chain scission by hydrolysis reaction. The permeation of sulfuric acid solution that affected the decomposition reaction was modeled and quantitative evaluation of permeation of sulfuric acid was established.     

Probing the mobility of supercooled liquid 3-methylpentane at temperatures near the glass transition using rare gas permeation

We study the diffusivity of three-methylpentane (3MP) using the permeation of inert gases (Ar, Kr, Xe) through the supercooled liquid created when initially amorphous overlayers are heated above T(g). We find that the permeation rates for all of the gases have non-Arrhenius temperature dependences that are well described by the Vogel-Fulcher-Tamman equation. Comparison with the literature viscosity shows that the Stokes-Einstein equation breaks down at temperatures approaching T(g). The fractional Stokes-Einstein equation, D ∝ (T∕η)(n), does fit the permeation data, albeit with different values of n for each gas. There is qualitative agreement with the Stokes-Einstein equation in that the permeation rate decreases with increasing radius of the rare gas probe, but the small differences in radii significantly underestimate the observed differences in the permeation rates. Instead the permeation rates are better correlated with the rare gas-3MP interaction energy than with the atomic radius.     

Differential permeation and absorption of water vapor in polyacrylamide film

An investigation has been made of successive differential absorption and differential permeation of water vapor in polyacrylamide a t 30°C. The successive differential ab sorptions showed two types of non-Fickian anomalies: sigmoid type and two-stage type curves. The experimental data have been analyzed in terms of the Fick diffusion equation assuming a time-dependent approach of the surface concentration. The calculated family of absorption curves agreed with the experimental results. The permeation curves in the region of high and low pressure increments were apparently normal, but at medium pressures they showed anomalous behavior. It was found that in the differential type of permeation experiment the stress effect induced by a concentration gradient between the surfaces of the film was eliminated. By assuming the time-dependent approach of the equilibrium surface concentration, we calculated the time lag as a function of film thickness and applied the theory to the data for permeation through polyacrylamide film with different film thicknesses a t relatively small pressure intervals. The rate parameter calculated from permeation data was found to be in good agreement with that from successive differential absorption data.     

Penetration of radionuclides across the skin: Rat age dependent promethium permeation through skin in vitro

The composition and the permeation properties of the skin are dependent on age. In the animal models for permation studies, age affects the mechanical as well as the permeation properties significantly. The time dependence of permeation of ¹⁴⁷Pm³⁺ from aqueous solution was established by the animal skin model and the age dependence of promethium permeation through the skin was examined. The aim was to find the optimum rat skin age model for radionuclide permeation studies and to assess the relative importance of the main permeation pathways: transepidermal and transfollicular permeation. The skin from 5-day-old rats (5DR) was found to represent the optimum animal model to study transepidermal permeation of ions. The skin from 9-day-old rats (9DR) was selected to study transfollicular permeation of ions. Comparison of the permeated amounts of promethium through the skin without hairs (3 DR to 6 DR) and with hairs (7DR to 12DR) showed that the additional permation mode via follicles significantly contributed to the permeation rate and extent.     

Surface processes in hydrogen permeation through metal membranes

The phenomenon of hydrogen permeation through metals is considered as a complex of interphase and diffusion processes. Basic principles of application of the hydrogen permeation technique to studies of various stages of hydrogen interaction with metals are formulated. An analysis is made of possible errors of the permeation technique when used to measure the characteristics of hydrogen diffusion through metals originating from the finite rate of the interphase processes. The permeation of nonequilibrium and corrosion-produced hydrogen through metal membranes, and the hydrogen permeability of multilayer systems are considered.     

Long-term stability of sulfur dioxide permeation tube standard reference materials

Summary A series of NIST (National Institute of Standards and Technology) sulfur dioxide permeation tubes from several Standard Reference Materials (SRMs 1625 and 1627) were studied for their long-term permeation characteristics at temperatures of 20, 25 and 30°C. It was found that contrary to previous reports the steady-state permeation rate was not constant, but showed a very slight downward trend with time. During the day-to-day use of such devices the downward trend in permeation rate is small enough to go unnoticed. In addition, the permeability at 30°C and permeability activation energy of SO₂ in FEP-Teflon are also evaluated for tubes that were part of the National Institute of Standards and Technology permeation tube SRM inventory from 1982 to 1989.     

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.     

Gas permeation processes in biogas upgrading: A short review

Biogas upgrading is a widely studied and discussed topic. Many different technologies have been employed to obtain biomethane from biogas. Methods like water scrubbing or pressure swing adsorption are commonly used and can be declared as well established. Membrane gas permeation found its place among the biogas upgrading methods some years ago. Here, we try to summarize the progress in the implementation of gas permeation in biogas upgrading. Gas permeation has been already accepted as a commercially feasible method for CO₂ removal. Many different membranes and membrane modules have been tested and also some commercial devices are available. On the other hand, utilization of gas permeation in other steps of biogas upgrading like desulfurization, drying, or VOC removal is still rather rare. This review shows that membrane gas permeation is able to compete with classical biogas upgrading methods and tries to point out the main challenges of the research.     

The use of permeation tube device and the development of empirical formula for accurate permeation rate

A series of laboratory experiments were conducted to assess the accuracy of permeation tube (PT) devices using a calibration gas generator system to measure permeation rate (PR) of volatile organic compounds (VOCs). Calibration gas standards of benzene, toluene, and m-xylene (BTX) were produced from PTs at varying flow rates (FR) of 20-1200 mL min(-1) and constant temperature (30°C). Results indicate that changes in flow rate greatly affected the permeation rate of each VOC at this temperature. This paper presents experimental approaches to accurately measure actual permeation rate (APR) and the derivation of empirical equations for predicted permeation rate (PPR). If the magnitude of bias is defined as the difference between PPR and the manufacturer's permeation rate (MPR), the bias was typically 19-40% for toluene (T) and 31-54% for m-xylene (X). Benzene (B) exhibited the least bias of 1.4-18.8%, nevertheless our PPR values for benzene were more reliable at lower flow rates (0.75-1.20%). This study highlights the importance of flow rate and associated pressure changes as a key to accurate permeation rate estimation from permeation tube devices.