Non-porous Layer Research Articles

Low pressure high flux thin film nanofibrous composite membranes prepared by electrospraying technique combined with solution treatment

In this study, high flux thin film nanofibrous composite (TFNC) membrane consisting of a nonwoven nanofibrous supporting layer and a thin hydrophilic barrier layer was developed and used as an ultrafiltration media to separate an oil/water emulsion at low feeding pressure. Firstly, the hydrophilic barrier layer was fabricated by electrospraying polyvinyl alcohol (PVA) on nanofibrous polyacrylonitrile (PAN) substrate. Secondly, the deposited PVA top layer was swollen to merge imperceptibly into an integrated barrier film on the supporting layer by immersing PVA/PAN double-layer membranes into suitable solvent water and nonsolvent acetone mixture, and then chemically crosslinked by glutaraldehyde in water/acetone solution. The water content of water/acetone solution and the immersion time were optimized to achieve the integrated and nonporous PVA barrier layer. Filtration performance of the resulting PVA/PAN TFNC membranes was evaluated by the oil/water emulsions separation system. Results showed that the optimized TFNC membrane possessed high flux (347.8l/m2h) with high rejection rate (99.6%) at very low feeding pressure (0.2MPa). It is believed that the strategy for fabricating TFNC membranes described here can be extended easily to fabricate TFNC membranes from many other polymeric membrane materials simply by choosing the suitable solution system for post-treatment.

Influence of the Amount of Master Alloy on the Properties of Austenitic Stainless Steel AISI 316L Powder Sintered in Hydrogen

AISI 316L austenitic stainless steel powder was modified with four different amounts of boron (0.1; 0.2; 0.3; 0.4 of wt. %) in the form of MasterAlloy micro-powder, and was sintered in a pure dry hydrogen atmosphere in order to obtain high density sintered samples characterized by a thickened non-porous surface layer. We investigated the influence of the amount of boron on: density, hardness, grain microhardness, porosity, microstructure and surface quality. The study revealed that it is possible by a conventional compacting and sintering process to obtain near full-density sintered samples with a non-porous superficial layer without boride precipitations.

One-pot synthesis of silica core–shell particles with double shells and different pore orientations from their nonporous counterparts

Silica core–shell particles (CSPs) have been successfully synthesized from their nonporous counterparts under basic conditions in the presence of the cationic surfactant cetyltrimethylammonium chloride and NH4F using a new one-pot templated dissolution and templated redeposition hybrid method. This method leads to high yield (∼85%) CSPs with an extremely narrow particle size distribution (no particle aggregation or fine particles) and allows us to vary reaction time to rapidly and conveniently control shell thickness up to the radius of the core particles. The resultant porous shells possess a unique double ordered pore arrangement with the inner and outer shells consisting of wormhole-like and radially oriented pores, respectively. To the best of our knowledge, this is the first report describing the fabrication of double shells in one step with the ability to manipulate the shell thickness from preformed silica particles in the presence of a surfactant. A mechanism to account for the formation of porous shells with different pore morphologies is presented. The resultant CSP particles have the combined characteristics of narrow particle distribution, narrow pore size distribution, unique double shells, and controlled shell thickness, surface area, and pore volume. These properties make them ideal candidates for fast and highly efficient chromatographic separation applications. The ability to control shell thickness while not dissolving the entire nonporous silica protective layer is particularly important to prepare functional core–shell particles (e.g., quantum dot core–nonporous silica shell–porous silica shell) for biomedical applications while avoiding toxic nanoparticles being directly exposed to the body. It is expected that this new hybrid synthesis method could be extended to generate a superficially porous silica layer with a controlled shell thickness and dual mesopore structure from any materials with a sol–gel silica coating.

Performance and penetration of laccase and ABTS inks on various printing substrates

Introduction of an enzyme and a colour-forming reagent into paper enables the development of an authenticity indicator. The purpose of this work was to study the performance of Trametes versicolor laccase, TvL, and ABTS, 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulphonic acid) diammonium salt, in various printing substrates when printed with inkjet. The printing substrates included pre-coated mechanical paper additionally coated with PVA, silica and latex. The focus was on the bioanalytical performance and ink penetration. The setting of the printed TvL and ABTS ink was studied visually, with optical and confocal microscopy and with a so-called tape laminating technique. Technical properties of the printing substrates and effect of the surface chemistry were discussed and related to the bioanalytical properties. TvL activity persisted well during the printing. The best colour response was attained using the PVA-coated base paper. The film-forming ability of the PVA was found to be the main contributor to the colour reaction. The uniform, dense and non-porous PVA layer retains the ABTS and TVL molecules on top of the printing substrate. The high local ink concentration on the PVA coating layer combined with the absorptive paper substrate suggests that the PVA film acts as a filtering layer which retains TvL and ABTS molecules in the coating layer but allows most of the ink solvents to penetrate into the paper structure. TvL and ABTS molecules are also trapped in the PVA polymer network due to swelling effect of water. Electrostatic attractions between the PVA and ABTS and TvL molecules do not contribute to the colour reaction.

Gd 2O 3:Eu 3+@mesoporous SiO 2 bifunctional core–shell composites: Fluorescence label and drug release

A novel kind of core–shell nanocomposite Gd 2O 3:Eu 3+@mesoporous SiO 2 was successfully fabricated, which consisted of a solvothermal synthesized Gd 2O 3:Eu 3+ nanospheres core, a thin nonporous silica midterm layer and an ordered mesoporous silica shell. The XRD, SEM, TEM, FTIR, N 2 adsorption/desorption and PL spectra were employed to characterize the composites. The cytotoxicity of Gd 2O 3:Eu 3+@mesoporous SiO 2 and Gd 2O 3:Eu 3+ was assessed by the standard MTT assay. The composites had spherically monodisperse morphology and a narrow size distribution around 180 nm in diameter. Furthermore, they also demonstrated the strong photoluminescence of 5D 0– 7F J emissions. In addition, the composites exhibited good property of sustained drug release by using ibuprofen (IBU) as model drug in the drug delivery process. Therefore, the drug release process could be easily tracked and identified through photoluminescence. Overall, the present composites have potential significant biomedical application as ideal bifunctional materials.

Effect of varying solvents compositions on morphology and gas permeation properties on membranes blends for CO 2 separation from natural gas

Asymmetric polysulfone/polyimide (PSF/PI) blended membranes were developed at compositions of 80/20, 50/50 and 20/80 for N-methyl-2-pyrrolidone/dichloromethane (DCM/NMP) solvent mixtures, in order to understand the mechanism of membrane formation for CO 2/CH 4 separation performance. Scanning electron microscopy (SEM) investigations showed that the membrane surfaces for all compositions were homogenous and their cross-sections showed non-porous top layer and porous substructure. Morphological analysis was further correlated with solubility parameter approach and coagulation value. Results showed that for NMP/DCM solvent mixtures, the solubility parameter difference to ethanol and polymeric membranes was in the order of 80/20 < 50/50 < 20/80. Among various compositions of NMP/DCM solvent mixtures, membranes prepared from (20/80) composition showed the lowest coagulation value. The compatibility of all the membrane blends was confirmed by using differential scanning calorimetry (DSC). Thermogravimetric analysis (TGA) showed that thermal stability was improved with PI addition in the membranes blends and PSF/PI-20% exhibited the maximum thermal degradation value ( T d ) of 549 °C. While gas permeation results showed maximum CO 2/CH 4 selectivity values in the range of 28.70–28.22 at 2–10 bar feed pressure respectively for PSF/PI-20% prepared from NMP/DCM with solvent composition of (80/20).

Evaluation of Tubular Poly(Trimethylene Carbonate) Tissue Engineering Scaffolds in a Circulating Pulsatile Flow System

Tubular scaffolds (internal diameter approximately 3 mm and wall thickness approximately 0.8 mm) with a porosity of approximately 83% and an average pore size of 116 µm were prepared from flexible poly(trimethylene carbonate) (PTMC) polymer by dip-coating and particulate leaching methods. PTMC is a flexible and biocompatible polymer that crosslinks upon irradiation; porous network structures were obtained by irradiating the specimens in vacuum at 25 kGy before leaching soluble salt particles. To assess the suitability of these scaffolds in dynamic cell culturing for cardiovascular tissue engineering, the scaffolds were coated with a thin (0.1 to 0.2 mm) non-porous PTMC layer and its performance was evaluated in a closed pulsatile flow system (PFS). For this, the PFS was operated at physiological conditions at liquid flows of 1.56 ml/s with pressures varying from 80-120 mmHg at a frequency of 70 pulsations per minute. The mechanical properties of these coated porous PTMC scaffolds were not significantly different than non-coated scaffolds. Typical tensile strengths in the radial direction were 0.15 MPa, initial stiffness values were close to 1.4 MPa. Their creep resistance in cyclic deformation experiments was excellent. In the pulsatile flow setup, the distention rates of these flexible and elastic scaffolds were approximately 0.10% per mmHg, which is comparable to that of a porcine carotid artery (0.11% per mmHg). The compliance and stiffness index values were close to those of natural arteries.?In long-term deformation studies, where the scaffolds were subjected to physiological pulsatile pressures for one week, the morphology and mechanical properties of the PTMC scaffolds did not change. This suggests their suitability for application in a dynamic cell culture bioreactor.

Modeling of Aniline Removal by Reverse Osmosis Using Different Membranes

AbstractThe behavior of different reverse osmosis membranes, namely, HR98PP, SEPA‐MS05, and DESAL‐3B, was compared with the one predicted by a solution‐diffusion model. This model assumes that the membrane has a homogeneous, nonporous surface layer and uses two main parameters, permeate concentration Cp and volumetric permeate flux Qp, to characterize the membrane system. In order to calculate these parameters, the theoretical values of water and solute permeability constants, Aw and Bs, and the osmotic pressure coefficient, Ψ, were initially determined. Using the software Sigma Plot V 10.0, accurate values of Ψ, Qp, and Cp were only obtained for the DESAL‐3B membrane, i.e., the selected solution‐diffusion model can be applied to this membrane.

Investigation of direct carbon conversion at the surface of a YSZ electrolyte in a SOFC

Fuel cells offer a promising way to produce electricity efficiently. In this work, a direct carbon fuel cell (DCFC) based on a solid oxide fuel cell (SOFC) has been investigated, in which solid carbon has been used as fuel in form of a pellet. The DCFC is an interesting technology because it offers the possibility to use, as fuel source, available and abundant raw materials with only minor pretreatment. Moreover, the thermodynamic efficiency slightly exceeds 100% in a wide temperature range due to the positive near-zero value of reaction entropy change. As pure carbon dioxide is produced at the anode, it can be easily captured and sequestered. Direct carbon conversion is competed by the Boudouard reaction, which produces carbon monoxide at high operating temperatures. This reaction is endothermic and leads to a fuel loss. The present paper relates to the contribution of both reactions by a long-term run over about 12 h with a non-porous anode layer.

CuO-loaded nano-porous SnO 2 films fabricated by anodic oxidation and RIE process and their gas sensing properties

The fabrication of nano-porous SnO 2 films with 1-D nano-channels by anodic oxidation has been a challenge due to a collapse of pore structure during annealing process and an existence of non-porous upper barrier layer. A new approach is developed to synthesize the nano-porous SnO 2 films by employing Sn thin film instead of Sn foil and a reactive ion etching (RIE) process. The integrity of nano-porous structure was maintained by anodizing the Sn thin film deposited on SiO 2/Si substrate, and 1-D nano-channels were opened up by removing the non-porous layer by RIE. As a potential application to gas sensor, CuO was impregnated to the nano-porous SnO 2 films and their gas sensing properties were investigated. The nano-porous CuO–SnO 2 film sensors exhibited the enhanced sensitivity and selectivity toward H 2S gas, and their H 2S sensing mechanism was discussed in terms of the formation/disruption of resistive p-CuO/n-SnO 2 junction based on the variation of XPS binding energy and electrical resistance during gas exposure.

Preparation of Compact Micro-Arc Oxidation Coatings on Aluminum Alloys

In this paper, a hard and thin coating with no loose layer was formed on the surface of the aluminum LC4 by bipolar micro-arc oxidation power, and the influence of ratio J of the negative current density to the positive current density on the thickness h and the hardness H of micro-arc oxidation coatings was studied. By SEM and other modern materials testing and analyzing techniques, the microstructures of the micro-arc oxidation ceramic coatings were tested and analyzed. It was showed that the micro-structure is compact, and the ceramic coating almost has non-porous layer.

Improvement of high temperature stability of Pd coating on Ta by HfN intermediate layer

Hafnium nitride (HfN) was chosen as a material for non-porous intermediate layer to improve the high temperature stability of Pd–Ta composite membranes for hydrogen separation. A layer of dense HfN (70 nm) was prepared between Ta substrate and thin Pd film (300 nm), and the high temperature stability of Pd coating was examined by hydrogen absorption experiments at 573 K after the heat treatments at 873 and 973 K. The HfN layer showed obvious hydrogen permeability, though the permeation rate in HfN appeared to be smaller than that in Pd and Ta. In addition, the degradation in coating effects of Pd at elevated temperatures was substantially retarded by HfN layer. Such improved stability was ascribed to retardation of open porosity development in Pd films and interdiffusion between Pd and Ta. It was concluded that HfN is a potential candidate material for intermediate layer to improve high temperature stability of Pd-group 5 metal composite hydrogen separation membranes.

Properties of A Metal Clad Waveguide Sensor Based on A Nanoporous-Metal-Oxide/Metal Multilayer Film

A metal-clad waveguide (MCWG) sensor comprised of a nanoporous waveguiding layer on a metal cladding layer is advantageous in sensing of biomolecules because of a high surface area of nanopores and a sharp dip in the reflection spectrum due to characteristics of the MCWG mode. Here, a porous anodic alumina (PAA)/aluminum (Al) film was fabricated on a glass substrate as a MCWG sensor with the Kretschmann geometry, and the sensor response was examined for both colorless bovine serum albumin (BSA) and colored metal complexes by measurements of reflection spectra and Fresnel calculations. The BSA adsorption on the PAA layer induced a parallel redshift of the waveguide coupling dip in the reflection spectrum. The experimental results were well simulated by the five-phase Fresnel calculations which indicated that the redshift of the dip was linearly dependent on the adsorbed amount of BSA. When the response of a MCWG sensor with a PAA layer was compared with that of a MCWG sensor with a nonporous alumina layer, the former showed larger redshift than the latter, due to a large adsorbed amount of BSA in the PAA layer with high surface area. For the adsorption of colored Ru[Bphen(3)](2+) and Fe[Phen(3)](2+), the effect of both the real and imaginary parts of the complex refractive index on the sensor response was examined. As a result, a redshift of the waveguide coupling dip was observed for both metal complexes irrespective of the wavelength region examined; this could be ascribed to the changes in the real part of the refractive index due to the adsorption of metal complexes on the PAA layer. Meanwhile, an increase in the reflectivity was observed when the coupling wavelength was close to that of the absorption bands of the metal complexes; this could be ascribed to the changes in the imaginary part of the refractive index of the PAA layer. Using the sensor response caused by the changes in the imaginary part, absorption spectral profiles of metal complexes could be reproduced.

Influence of Citric and Ascorbic Acids on Electrodeposited Au/FeAu Multilayer Nanowires

AuFe electrodeposits onto a rotating disk electrode were examined to assess the composition and current efficiency behavior when citric acid, ascorbic acid, or a combination of both is present in the electrolyte. Nanowires were subsequently fabricated with pulsed current deposition to create compositionally, multilayered Au/FeAu nanowires. The FeAu layer of the nanowires was porous in a citrate electrolyte, but the porosity decreased with the addition of ascorbic acid in the electrolyte. Comparatively higher side reaction partial current densities in the citric acid electrolyte generated local alkaline conditions, inducing the chemical precipitation of Fe ions in the form of iron oxide nanoparticles inside the recess, which manifested as the regions of high porosity. Nonporous layers observed in the ascorbic acid bath, in combination with decreased and increased current efficiency of the deposits, suggested that a similar mechanism of Fe precipitation inside the nanorecess is less likely.

Ti-Rich Barrier Layers Self-Formed on Porous Low-k Layers Using Cu(1 at.% Ti) Alloy Films

To investigate the applicability of the technique of barrier self-formation using Cu(Ti) alloy films on porous low-k dielectric layers, Cu(1 at.% Ti) alloy films were deposited on porous SiOCH (low-k) dielectric layers in samples with and without ~6.5-nm-thick SiCN pore seals. Ti-rich barrier layers successfully self-formed on the porous low-k layer of both sample types after annealing in Ar for 2 h at 400°C to 600°C. The Ti-rich barrier layers consisted of amorphous Ti oxides and polycrystalline TiC for the samples without pore sealing, and amorphous TiN, TiC, and Ti oxides for the pore-sealed samples. The amorphous TiN originated from reaction of Ti atoms with the pore seal, and formed beneath the Cu alloy films. This may explain two peaks of Ti segregation at the interface that appeared in Rutherford backscattering spectroscopy (RBS) profiles, and suggests that the Ti-rich barrier layers self-formed by the reaction of Ti atoms with the pore seal and porous low-k layers separately. The total molar amount of Ti atoms segregated at the interface in the pore-sealed samples was larger than that in the samples without pore sealing, resulting in lower resistivity. On the other hand, resistivity of the Cu alloy films annealed on the porous low-k layers was lower than that annealed on the nonporous low-k layers. Coarser Cu columnar grains were observed in the Cu alloy films annealed on the porous low-k layers, although the molar amount of Ti atoms segregated at the interface was similar in both sample types after annealing. The cause could be faster reaction of the Ti atoms with the porous dielectric layers.

Kinetics of sphalerite bioleaching by Acidithiobacillus ferrooxidans

In the present study, the effect of some important parameters including particle size, pulp density and temperature on the rate of Zn dissolution from sphalerite concentrate by Acidithiobacillus ferrooxidans was investigated. The highest rate of sphalerite bioleaching was obtained at particle size, pulp density and temperature of 38–150 μm, 4% wt/vol and 33 °C respectively. The formation of a product layer over sphalerite concentrate particles was confirmed by SEM images whereas XRD, EDS and BET analysis showed that this layer is composed of elemental sulfur and is non-porous. Based on these results, it was decided that a kinetic model in which the rate of Zn dissolution is limited by diffusion of ions through a non-porous product layer is appropriate to describe the sphalerite bioleaching process. Determinations of ferrous iron ion concentration during bioleaching showed that the concentration of this ion varies significantly during bioleaching and hence the kinetic model was revised to take account of this fact. The predictions of this model had a good compatibility with the experimental data and the value of activation energy was determined as 39 kJ/mol.

Ellipsometry porosimetry (EP): Thin film porosimetry by coupling an adsorption setting with an optical measurement, highlights on diffusion results

Ellipsometry porosimetry (EP) is an emerging technique that is dedicated to porous thin films analysis; it is non-contact and non-destructive. EP tools developed at SOPRALAB, allows us to obtain adsorption isotherms with many different adsorptives at an ambient temperature. EP leads to the same results as classical adsorption experiments (e.g. porosity and pore size distribution), but it also has some particular features leading to new information. For instance, our optical setup (Spectroscopic Ellipsometry) allows us to determine the variation of the thickness of the samples during the adsorption experiment. It is also very sensitive to interfaces; it is thus possible to detect a porosity gradient or to study a bi-layer sample and plot the two corresponding adsorption isotherms at the same time [A. Bourgeois, A. Brunet-Bruneau, V. Jousseaume, N. Rochat, S. Fisson, B. Demarets, J. Rivory, Description of the porosity of inhomogeneous MSQ films using solvent adsorption studied by spectroscopic ellipsometry in the visible range, Thin solid films 455–456 (2004) 366]. For porous thin films with a non-porous barrier layer deposited on top, it is also possible to study the lateral diffusion phenomenon in the film (see figure below). In this paper, we will illustrate a part of the different features of EP for adsorption on porous thin films and more particularly for diffusion phenomenon.

Mechanisms of transfer of ionic solutes through composite polymer nano-filtration membranes in view of their high sulfate/chloride selectivities

A number of nano-filtration membranes exhibit quite high rejections of sulfates (98–99%) accompanied by quite moderate rejections (sometimes as low as 10–20% and even less) of chlorides from highly concentrated electrolyte solutions like sea water or various brines. In this communication, it is shown that this phenomenon can hardly be explained within the scope of commonly accepted model of nano-filtration where the barrier layer is considered a nano-porous medium, and, accordingly, there is a considerable convective coupling between the transfers of solutes and solvent. The very high experimentally observed sulfate/chloride selectivities turn out hardly reconcilable with the quite moderate values of rejection of NaCl. It is suggested that this phenomenon can be explained by the solution-diffusion mechanism of solute transfer across very thin and practically non-porous barrier layers. The approach of rejection to non-100% apparent saturation values observed experimentally can be explained by the concentra...

Structural change and improvement of the mechanical properties of a lotus-type porous copper by wire-brushing

The surface of lotus-type porous copper plates that had cylindrical open pores in the thickness direction (porosity 50.4%, average pore diameter 144.4 μm) were processed by wire-brushing. Open pores on the surface of the lotus copper are closed by a newly formed nonporous thin layer. Electron backscatter diffraction patterns of the processed plate cross section show that the deformed surface consists of ultra-fine grains and that a nonporous layer was formed on the deformation of the surface layer. The Vickers hardness of the wire-brushed lotus copper is higher than that of the wire-brushed non-porous copper. The Vickers hardness increases with the increase in the rate of revolution of the wire–brush due to grain refinement. The increment of the ultimate tensile strength of lotus copper by wire-brushing is larger than of non-porous copper. The increment of ultimate tensile strength of the lotus copper reaches maximum when the newly deformed layer closes all the pores on the surface. These results show that wire-brushing is an effective process for the improvement of mechanical properties for lotus metals.

Preparation of pilot-scale inner skin hollow fiber pervaporation membrane module: Effects of dynamic assembly conditions

The purpose of this study is to provide some fundamental understanding for the design of industrial hollow fiber pervaporation membrane module. Inner skin hollow fiber pervaporation membrane modules were fabricated by a dynamic negative pressure layer-by-layer (LbL) technique. The influences of dynamic negative pressure and recycling velocity of polyelectrolyte solutions on the formation of non-porous selective layer were firstly investigated using mini-modules during the dynamic assembly process. Since none of reported works dealt with the effects of packing density of hollow fiber module, pilot-scale modules (diameter × length = 1 in. × 20 cm) were therefore prepared by filling different amounts of hollow fibers into a membrane shell. The experimental results show that the higher packing density of 500 m 2/m 3 rendered both total flux and selectivity to decrease significantly. As for a 1 m long module that has been commonly used in industry, further investigations were conducted using a 1-m long hollow fiber module. The vacuum drop along the axial direction of hollow fibers was noted, especially near to the vacuum suction opening. Despite of this, the relatively high and stable selectivity could be obtained even the fiber length increased to 1 m.