Simulation of water permeability and water vapor diffusion through hardened cement paste

The transport properties of cement-based materials significantly affect their durability. This results from the fact that most of the damaging reagents are transported, often solved in water, through the open pore space into the microstructure. This paper focuses on simulating water permeation (movement under a gradient of pressure) and water vapor diffusion (movement under a gradient of concentration) through hardened cement paste (hcp). The main goal is to derive the water permeability and the water vapor diffusion coefficient directly from the morphology of the 3D microstructure. For this purpose microtomographic images of a hcp made of ordinary Portland cement are used to represent the microstructure and especially the pore space through which the moisture transport will occur. With the use of a skeletonization algorithm, also known as “thinning algorithm”, the skeleton or centerline of the pore space is extracted. This skeleton is in a second step converted into a transportation network of cylindrical tubes. Bernoulli's law is applied to every tube for simulating water permeation. The permeability coefficient is then calculated by using Darcy's law. In the case of water vapor diffusion the diffusion coefficient is calculated using Fick's law. An erratum to this article is available at .     

Gas Permeation through Vacuum Materials

The aim of this research is to study the gas permeability of materials being used to create elements of unmanned aerial vehicles. The measurement system for gas permeation coefficients of composite materials is designed on the basis of a helium leak detector. Due to permeation through the Viton sealing the smallest flow that can be correctly measured by the system is 10^‐10 Pa · m³/s. Verification of the system was held on PTFE polymer sample with a known helium permeability value. Gas permeability of three composite materials was studied. The steadystate helium permeation coefficient in [Pa · m³/s] · [m/(m² · bar)] for high molecular weight polyethylene (HM‐WPE) with 100 nm copper coating is 3.1 · 10^‐8, for low pressure polyethylene (HDPE 209‐07) with 100 nm copper coating it is 1.9 · 10^‐7; for vacuum‐tight ceramics VK94‐1 with glue K400 layer it is 2.2 · 10^‐9. Authors will be glad to measure the gas permeability of new materials that can be provided by readers of this publication.     

Properties of Transglutaminase Crosslinked Whey Protein Isolate Coatings and Cast Films

Whey protein is an excellent barrier material, potentially providing the low oxygen permeability and water vapour transmission rate required for packaging materials for sensitive foods. A topical issue is how to reduce the permeability of the whey protein‐based layers. One possible strategy is to apply crosslinking agents. In the present study, the enzyme transglutaminase (TG) was used for this purpose, and the following properties have been measured: oxygen permeability, water vapour transmission rate, effective water vapour diffusion, sorption and permeation coefficients, swellability, light transmission and surface energy. The use of TG was found to reduce the oxygen permeability, reduce the water vapour transmission rate and reduce the effective water vapour diffusion coefficient of the whey protein layers. This study also showed that it was possible to use sorption experiments to approximate the water vapour transmission rates. This work is novel because it deals with the packaging‐related properties of whey films crosslinked with TG. Previous studies have focused on the influence of TG on protein formulations or on the measurement of film properties, which is of little relevance for packaging applications. Copyright © 2014 John Wiley & Sons, Ltd.     

Die Gasdurchlässigkeit von Vakuummaterialien

This work presents investigations on the gas permeability of materials for use in unmanned space vehicles. The measurement system for determining the gas permeation coefficients of composite materials is designed on the basis of a helium leak detector. Due to permeation through the Vi-ton sealing the smallest flow that can be correctly measured by the system is 10⁻¹⁰ Pa · m³/s. The system was assessed with a PTFE polymer sample with a known helium permeability value. Furthermore, the gas perme-abilities of three composite materials were studied. The steady-state helium permeation coefficient in [Pa · m³/s] · [m/(m² · bar)] for high molecular weight polyethylene (HM-WPE) with 100 nm copper coating is 3.1 · 10⁻⁸, for high density polyethy lene (HDPE 209-07) with 100 nm copper coating it is 1.9 · 10⁻⁷; for vacuum-tight ceramics VK94-1 with glue K400 layer it is 2.2 · 10⁻⁹. Authors will be glad to measure the gas permeability of new materials that can be provided by readers of this publication.     

Permeation and Sorption of Water and Gases Through EVA Copolymers Films

The transport of water and gases (pure oxygen and carbon dioxide) through poly(ethylene-co-vinyl acetate) (EVA) films of different VA contents and through a low density polyethylene LDPE (used as reference with 0 wt.% VA), was analysed by permeation and sorption measurements. In the case of water, for EVA of 70 wt.% VA, a plasticization effect on the material was observed. For EVA of 19 wt.% VA, there was no plasticization, while for EVA of 4.5 wt.% VA and for LDPE, the water diffusion coefficient decreases with increasing water. An empirical law was then found to account for the reduction of the water diffusivity. A negative plasticization effect was attributed to the formation of water clusters in these rather non polar polymers. This latter result was confirmed by sorption measurements and infra-red spectroscopy. The increase in water sorption extent with the VA content leads to a steady increase in the water permeability in the EVA copolymers. In the case of gas permeation, both for O₂ and CO₂ and whatever the VA content of the copolymer used, the experimental curves are characterized by a constant diffusion coefficient. This is confirmed by sorption experiments. In terms of gas permeability, EVA copolymers are characterized by low coefficients especially for oxygen. In the EVA rubbery copolymers, The O₂ solubility coefficient does not increase with the VA content due to the lack of polar interactions, while the CO₂ one increases due to the overall interactions between CO₂ induced dipoles and the polar the VA carbonyl groups. For these copolymers, the H₂O/CO₂ and H₂O/O₂ selectivities are very high. The experimental values of the selectivities indicate that these EVA copolymers appear as good candidates for applications using high perm-selectivity properties. Electronic Publication     

Water sorption and diffusion coefficient through an experimental dental resin

Polymeric composites have been widely used as dental restorative materials. A fundamental knowledge and understanding of the behavior of these materials in the oral cavity is essential to improve their properties and performance. In this paper we computed the data set of water absorption through an experimental dental resin blend using specimen discs of different thicknesses to estimate the diffusion coefficient. The resins were produced using Bisphenol A glycol dimethacrylate, Bisphenol A ethoxylated dimethacrylate and Triethylene glycol dimethacrylate monomers. The water sorption test method was based on International Standard ISO 4049 “Dentistry-Polymer-based filling materials”. Results show a diffusion coefficient around 6.38 × 10⁻⁸ cm²/s, within a variance of 0.01%, which is in good agreement with the values reported in the literature and represents a very suitable value.     

Polymer coating method developed for carbon stripper foils

The problem of handling the fragile carbon foils (mounting on the frame, placing in the stripper changer) that easily break when self-supporting has been solved by coating carbon foils with poly-monochloro-para-xylylene. It was found that the polymer-coating method could also be used to produce carbon foils thicker than 100 μg/cm² by alternated deposition of carbon and poly-monochloro-para-xylylene layers. Carbon foil of 500 μg/cm² thick and 10 cm in diameter was produced by this method and mounted to a foil holder. Results of lifetime measurement for singly coated foils are also presented.     

A Predictive Instrument for Sensitive and Expedited Measurement of Ultra-Barrier Permeation

The reliable operation of flexible display devices poses a significant engineering challenge regarding the metrology of high barriers against water vapor. No reliable results have been reported in the range of 10^–6 g∙(m²∙d)⁻¹, and there is no standard ultra-barrier for calibration. To detect trace amount of water vapor permeation through an ultra-barrier with extremely high sensitivity and a greatly reduced test period, a predictive instrument was developed by integrating permeation models into high-sensitivity mass spectrometry measurement based on dynamic accumulation, detection, and evacuation of the permeant. Detection reliability was ensured by means of calibration using a standard polymer sample. After calibration, the lower detection limit for water vapor permeation is in the range of 10^–7 g∙(m²∙d)⁻¹, which satisfies the ultra-barrier requirement. Predictive permeation models were developed and evaluated using experimental data so that the steady-state permeation rate can be forecasted from non-steady-state results, thus enabling effective measurement of ultra-barrier permeation within a significantly shorter test period.     

Systemic enhancement of papaverine transdermal gel for erectile dysfunction

To enhance the systemic transdermal delivery of papaverine for the treatment of erectile dysfunction, several factors that influence transdermal delivery of papaverine HCl were studied. The effects of membrane types for in vitro permeation study, human skin layers, solvent/cosolvent systems and the penetration enhancers on the transdermal permeation of papaverine HCl were investigated. A combination of caproic acid, ethanol and water in the volume ratio of 50%:30%:20% was chosen as penetration enhancer and incorporated in two gel bases: 18% Pluronic F-127 and 2% Carbopol 940. In vivo skin permeation studies were performed with two loading doses (0.6% and 2%) in rabbits. The flux and permeability coefficient of papaverine HCl through different human skin layers suggested that the major barrier layer for papaverine HCl was residing primarily in the stratum corneum. However, the viable epidermis and dermis layer also contributed certain degrees of diffusion resistance. Differential Scanning Calorimetry study showed that penetration enhancer exhibited a counter effect with papaverine HCl on the temperature and enthalpy in both gels. In vitro drug release study demonstrated significant increases in the steady-state flux, permeability coefficient and enhancement ratio in these gels. Faster drug transports and higher bioavailability were also observed in rabbits. Skin irritation test performed in rabbits demonstrated a mild skin reaction with mean PII scores of 2 and below; however the recovery was fast. In conclusion, caproic acid, ethanol and water in the volume ratio of 50%:30%:20% is an effective penetration enhancer to deliver papaverine HCl transdermally for systemic absorption.     

Salt diffusion in brick structures Part II The effect of temperature, concentration and salt

This is our second article concerning salt diffusion measurements in porous brick materials. In the first article a method for measuring the rate of diffusion of salt in ceramic material was presented and applied to the measurement of diffusivity of NaCl in different brick materials. In this work the same method was applied to other water-soluble salts commonly found in building materials. The binary diffusion coefficients were measured for KCl, NaNO₃, CaCl₂, Na₂SO₄, MgCl₂ and Na₂CO₃. The result for the diffusivity of 0.05 molar salts in water in new Finnish red brick varied between (0.271–0.544)*10^–5 cm²/s at a temperature of 25 ± 0.05°C. The effect of temperature and concentration on the diffusivity of NaCl in new red brick was also measured. The rate of change of diffusivity as a function of temperature, concentration and the type of salt was very similar to that in free solutions. However, the values of the diffusion coefficients were lower in the porous medium than in solution. A mutual relation between the binary diffusion coefficient and the viscosity of the salt-water solution was observed in the porous brick.     

Measurement of permeability for packaging films to d-limonene vapour at low levels

A method that utilizes permeation cells in conjunction with gas chromatography was developed to measure permeation of d-limonene vapour through packaging materials at very low gradient concentrations. The same method, when properly adjusted, can be used to determine the effect of temperature and relative humidity on permeation. The suitability of the method for its intended use was demonstrated by generating permeation data for polyester (Mylar) and oriented polypropylene (OPP) films at d-limonene vapour concentration gradients as low as 0.54 ppm. The ability to measure permeability at such low concentration levels, where the permeability coefficient approaches a virtually constant value, is of considerable importance. The permeation behaviour of packaging materials at even lower concentrations, most typical of foods, can be obtained by extrapolation. Thus, flavour loss through the package and shelf-life can be estimated in a more reliable manner.     

球体吸收法测量建筑材料水蒸气扩散系数的研究

以典型多孔建筑材料加气混凝土为例,搭建了球体吸收法测量水蒸气扩散系数的实验台,通过不确定度分析及方法验证,探究了球体吸收法测量建筑材料水蒸气扩散系数的可行性与准确性。得到结论:球体吸收法适用于测量多孔建筑材料的水蒸气扩散系数,且具有测量时间短、测量结果较准确等优点;对于加气混凝土来说,使用半时法计算水蒸气扩散系数比使用矩量法更加准确;加气混凝土的水蒸气扩散系数在相对湿度45%～80%之间逐渐增大,而在更高湿度中,由于液态水的出现,使得水蒸气扩散系数逐渐减小。     

High-Throughput Evaluation of Non-Swellable Controlled Release Matrix Tablets

Abstract

Drug release from controlled-release (CR) matrix tablets involves the permeation and diffusion of water through the system. In this study, a new methodology is proposed for the measurement of water permeation and simultaneous drug release from the inert, non-swellable CR matrix tablet of diltiazem (DLT) and a correlation is made between these two processes. Cylindrical matrices were readily prepared by direct compression of pellets obtained by extrusion-spheronization. Water transport was studied using tritiated water (HTO) as a permeant in a Franz-diffusion cell and simultaneously drug release was measured. Further, dissolution was performed on USP XXI/XXII dissolution apparatus I using demineralized water. Matrices showed a steady water-uptake up to 6 h and the steady state for HTO permeation lasting from 6-h to 24-h Flux of water permeated and flux of drug released correlated well. Thus, HTO permeation through the matrix tablet and the proposed methodology can be used as a tool and/or surrogate marker for evaluation of controlled release matrix tablets. This methodology can be coined as “high-throughput” in terms of amount of labor and resources required in comparison to that of dissolution.     

Systemic enhancement of papaverine transdermal gel for erectile dysfunction

To enhance the systemic transdermal delivery of papaverine for the treatment of erectile dysfunction, several factors that influence transdermal delivery of papaverine HCl were studied. The effects of membrane types for in vitro permeation study, human skin layers, solvent/cosolvent systems and the penetration enhancers on the transdermal permeation of papaverine HCl were investigated. A combination of caproic acid, ethanol and water in the volume ratio of 50%:30%:20% was chosen as penetration enhancer and incorporated in two gel bases: 18% Pluronic F-127 and 2% Carbopol 940. In vivo skin permeation studies were performed with two loading doses (0.6% and 2%) in rabbits. The flux and permeability coefficient of papaverine HCl through different human skin layers suggested that the major barrier layer for papaverine HCl was residing primarily in the stratum corneum. However, the viable epidermis and dermis layer also contributed certain degrees of diffusion resistance. Differential Scanning Calorimetry study showed that penetration enhancer exhibited a counter effect with papaverine HCl on the temperature and enthalpy in both gels. In vitro drug release study demonstrated significant increases in the steady-state flux, permeability coefficient and enhancement ratio in these gels. Faster drug transports and higher bioavailability were also observed in rabbits. Skin irritation test performed in rabbits demonstrated a mild skin reaction with mean PII scores of 2 and below; however the recovery was fast. In conclusion, caproic acid, ethanol and water in the volume ratio of 50%:30%:20% is an effective penetration enhancer to deliver papaverine HCl transdermally for systemic absorption.     

Dynamic permeation method to determine partition coefficients of highly hydrophobic chemicals between poly(dimethylsiloxane) and water

Measurement of partition coefficients between poly(dimethylsiloxane) (PDMS) and water (KPDMSw) becomes more and more difficult as the hydrophobicity of the compound increases. Experimental challenges include long extraction times, sorption to various surfaces and materials, and incomplete dissolution of the compound in the aqueous phase. In order to avoid these artifacts and to shorten experimental time, a dynamic permeation method was developed. According to steady-state diffusion theory, KPDMSw is inversely proportional to the permeation rate through the aqueous boundary layer (ABL) from the donor PDMS to the acceptor PDMS. A simple ABL permeation reactor can thus be applied to determine KPDMSw values of hydrophobic chemicals within a few days. The obtained values were in good agreement with those obtained using a conventional shaking method and the partition controlled delivery system. A good linear correlation was obtained between the logarithm of the 1-octanol/water partition coefficient (log Kow) from the literature and log KPDMSw over 6 orders of magnitude.     

Characterization of coatings on materials for components in fission and fusion reactors

With regard to applied materials fission and fusion reactors show corresponding properties: iron- and nickel-based alloys resistant to high temperatures are used as well as graphites, and in both systems special precautions have to be taken to minimize uncontrolled tritium release; in fission reactors, especially in high temperature gas-cooled reactors, corrosion of the metallic components plays a life-limiting role whereas in fusion reactors erosion, by chemical and physical processes, is of similar or still higher importance. A possible way to overcome some of the materials problems arising in both fission reactors and fusion reactors is to use materials coated with protecting layers optimized for the special problem. Here, one example will be discussed to highlight the application of coated materials in reactor technology for the reduction of hydrogen isotope permeation through metallic walls.For this purpose, a coating process is used for the production of the layers by which the hydrogen isotope permeation will be reduced. In this case, the alloys are subjected to an oxidation process—either by special pre-oxidation or in situ. Thus a surface oxide layer is formed. This layer is suitable for the reduction of tritium permeation when its structure and chemical composition fulfils certain conditions. The structural and chemical characterization of the oxide layer is discussed, and the conditions under which a convenient surface oxide layer can grow are described. The permeation-impeding factors achieved are specified for the different types of oxide scale.     

多道环氧涂层在NaCl溶液中的电化学阻抗谱

采用电化学阻抗谱(EIS)方法研究了环氧涂层的厚度与涂装道数对水传输行为的影响结果表明,水分子在具有良好阻挡作用的多道环氧涂层的初始阶段的传输符合Fick定律,求得了水在涂层中的表观扩散系数值,与之相应的干环氧涂层的介电常数εd为4.2.涂层越厚,涂装的道数越多,介质在涂层中的传输越困难,涂层的抗渗透性能越好多道环氧涂层的涂层电容-时间曲线类似于理想情况下单道涂层在水溶液中的涂层电容与浸泡时间的关系曲线.     

Electrical conductivity of Pd47Ni47Si6 amorphous membrane while hydrogen permeation

Hydrogen diffusion through an amorphous membrane causes local disorders in the structure which can be detected through the measurement of changes of the electrical conductivity. Detecting these changes and comparing them directly with the amount of the permeated hydrogen provides information on the efficiency of separation, which can be used in hydrogen sensor and analyzer technology. This paper presents the results of electrical resistivity measurement of Pd₄₇Ni₄₇Si₆ alloy amorphous membrane while hydrogen permeation flux was being changed along with the temperature. It was found that hydrogen changes the nature of the resistivity and the temperature coefficient of resistivity is negative, however, starting from the temperature of 365 K, its value becomes smaller. In order to explain this phenomenon thorough and detailed measurements of phase transitions were made with the use of differential scanning calorimetry and X-ray diffractometry. On the basis of the research an attempt was made to explain the recorded changes of electrical conductivity.     

A study of very thin DLC foils as a gas barrier

Measurements of vacuum tightness and mechanical strength of diamond-like carbon (DLC) foils in the thickness range of 1–7 μg cm⁻² have been performed with a purpose to evaluate suitability of foils as a gas barrier. Hydrogen and argon at pressures from 10⁻² Pa to 20 kPa were used as test gases. The permeation rate specified as conductance density was found for the best sample of self-supporting foil to be around 1.5×10⁻³ l and 3.3×10⁻⁴ l s⁻¹ cm⁻² for H₂ and Ar, respectively. Conductance density of the same foils mounted on the frames with a mesh along the apertures as support was about twice higher than that for the self-supporting ones, likely due to the mechanical imperfections of the foil assemblies of the first ones. On the other hand, mesh-supported foils as thin as 3 μg cm⁻² and of 5 mm in diameter were withstanding the pressure of up to 18 kPa, while self-supporting foils of the same thickness ruptured at around 1.2 kPa. There was no observed relation between thickness of the foil and its mechanical properties and permeation rate. This suggests that rather tears and pinholes present in foils are the limiting factors of the foil–vacuum tightness and strength. Results obtained in the studies, presented in this work, demonstrate the ability of very thin DLC to isolate a high vacuum beam line from a gas cell in a variety of applications and ability to withstand the gas pressure relevant, in particular, to some gas-filled ionization chambers.