Porous Polytetrafluoroethylene Membrane Research Articles

Quaternized polyepichlorohydrin/PTFE composite anion exchange membranes for direct methanol alkaline fuel cells

Novel composite anion exchange membranes have been prepared using polyepichlorohydrin (PECH) to avoid chloromethylation. PECH is first quaternized with N, N, N′, N′- tetramethyl-1,6-hexane diamine (TMHDA) and then combined with porous polytetrafluoroethylene (PTFE) membranes to form composite anion exchange membranes of quaternized PECH(QPECH)/PTFE. The membranes are characterized via scanning electron microscopy (SEM), Fourier transform infrared (FTIR), X-ray diffraction (XRD) and thermogravimetric analysis (TGA). Water uptake, ionic exchange capacity, ionic conductivity and methanol permeability are measured to evaluate their performance in a direct methanol alkaline fuel cell. SEM results indicate that QPECH has penetrated into the pores of the PTFE membranes. The membranes exhibit high ionic exchange capacity and ionic conductivity. The ionic conductivity is in the range 3.60–6.23×10−2Scm−1 at the temperature range 30–80°C. The membranes have good thermal stability under an air atmosphere and are stable in basic media with KOH concentration up to 8M at 30°C.

Carbon nanohorns accelerate bone regeneration in rat calvarial bone defect

A recent study showed that carbon nanohorns (CNHs) have biocompatibility and possiblemedical uses such as in drug delivery systems. It was reported that some kinds of carbonnanomaterials such as carbon nanotubes were useful for bone formation. However, theeffect of CNHs on bone tissue has not been clarified. The purpose of this study was toevaluate the effect of CNHs on bone regeneration and their possible application for guidedbone regeneration (GBR). CNHs dispersed in ethanol were fixed on a porouspolytetrafluoroethylene membrane by vacuum filtration. Cranial defects were created inrats and covered by a membrane with/without CNHs. At two weeks, bone formation underthe membrane with CNHs had progressed more than under that without CNHs andnumerous macrophages were observed attached to CNHs. At eight weeks, there was nosignificant difference in the amount of newly formed bone between the groups and theappearance of macrophages was decreased compared with that at two weeks. Newly formedbone attached to some CNHs directly. These results suggest that macrophages induced byCNHs are related to bone regeneration. In conclusion, the present study indicatesthat CNHs are compatible with bone tissue and effective as a material for GBR.

A Polytetrafluoroethylene/quaternized polysulfone membrane for high temperature polymer electrolyte membrane fuel cells

A polytetrafluoroethylene (PTFE)/quaternized polysulfone (QNPSU) composite membrane has been fabricated for use in proton exchange membrane fuel cells (PEMFCs). The composite membrane is made by immobilising a QNPSU solution into a hydrophobic porous PTFE membrane. The structure of the composite membrane is examined by SEM and EDX. The ionic conductivity of the PTFE/QNPSU membrane, at a relative humidity lower than 0.5% and a temperature of 180 °C, is greater than 0.3 S cm-1, when loaded with 400% H3PO4. A hydrogen fuel cell with this membrane operating at 2.0 atmosphere absolute (atma) pressure and 175 oC gives voltages > 0.4 V at current densities of 1.0 A cm-2 using oxygen.

A developed asymmetric PVDF hollow fiber membrane structure for CO 2 absorption

Carbon dioxide (CO 2), the main greenhouse gas, has been associated with global climate change. Therefore, it is important to develop technologies to mitigate this issue. In present study, porous hydrophobic polyvinylidene fluoride (PVDF) hollow fiber membranes with developed structure for CO 2 absorption were prepared via a wet spinning process. The prepared membranes were characterized in terms of morphology examination, gas permeability, critical water entry pressure (CEP w) and mass transfer resistance. From the morphology examination, the membrane showed an almost sponge-like structure with inner skinless layer and ultra-thin outer skin layer. Results of gas permeation test indicated that the membrane possess very small mean pore size (3.96 nm) with high surface porosity. The CO 2 absorption experiment demonstrated a significant improvement in the CO 2 flux of the prepared PVDF membrane compared to the commercial porous polytetrafluoroethylene (PTFE) hollow fiber membrane. At the absorbent flow rate of 200 ml/min, CO 2 flux of the PVDF membrane (4.10 × 10 −4 mol/m 2 s) was approximately 68% higher than the CO 2 flux of the PTFE membrane. In addition, the results indicated that an approximate 25% CO 2 flux reduction was gradually occurred at initial 26 h, then the CO 2 flux maintained constant over 140 h of the operation.

New Double-Band-Electrode Channel Flow Differential Electrochemical Mass Spectrometry Cell: Application for Detecting Product Formation during Methanol Electrooxidation

We present a new double-band-electrode channel flow DEMS (differential electrochemical mass spectrometry) cell and demonstrate its application in mechanistic studies with particular relevance to fuel cells. The cell is composed of two band electrodes, which serve as working and detecting electrodes, respectively, separated by a porous Teflon membrane. The Teflon membrane serves as the interface between the aqueous solution and vacuum, through which gases and volatile species can be transported. The hydrodynamic electrochemical characteristics and mass spectrometric behavior have been characterized. With this DEMS cell, gaseous and volatile electrochemical products formed at the working electrode are monitored by mass spectrometry, while nonvolatile products can be selectively detected at the detecting (downstream) electrode. Thus, this system can be considered as the DEMS analogue of a rotating ring/disk electrode. As test cases, the electrooxidation of formaldehyde and methanol on carbon supported Pt nanoparticle catalysts have been studied using this new channel flow DEMS cell.

Evaluation of the Sensitivity of Hydrogen Sensors Covered with Polytetrafluoroethylene as a Protective Membrane for Humidity

Environmental factors such as dust adsorption effects and humidity generally result in drifts of the sensor output signal and lead to malfunctions of the sensor and/or reduction in sensitivity. So a sensor package is necessary to protect hydrogen sensors in order to operate the sensors in an actual use environment. In this study, a Pt-FET hydrogen sensor covered with a polytetrafluoroethylene (PTFE) porous membrane was developed. The PTFE porous membrane with different pore sizes of 5 μm, 20 μm, and 30 μm was applied and the effects of humidity on sensor sensitivity were evaluated. The results indicate the effects of humidity on the sensitivity were reduced in the relative humidity range between 20% and 80% for the sensor with the 5-μm porous membrane.

A chemical ionization mass spectrometer for continuous underway shipboard analysis of dimethylsulfide in near-surface seawater

Abstract. A compact, low-cost atmospheric pressure, chemical ionization mass spectrometer ("mini-CIMS") has been developed for continuous underway shipboard measurements of dimethylsulfide (DMS) in seawater. The instrument was used to analyze DMS in air equilibrated with flowing seawater across a porous Teflon membrane equilibrator. The equilibrated gas stream was diluted with air containing an isotopically-labeled internal standard. DMS is ionized at atmospheric pressure via proton transfer from water vapor, then declustered, mass filtered via quadrupole mass spectrometry, and detected with an electron multiplier. The instrument described here is based on a low-cost residual gas analyzer (Stanford Research Systems), which has been modified for use as a chemical ionization mass spectrometer. The mini-CIMS has a gas phase detection limit of 220 ppt DMS for a 1 min averaging time, which is roughly equivalent to a seawater DMS concentration of 0.1 nM DMS at 20°C. The mini-CIMS has the sensitivity, selectivity, and time response required for underway measurements of surface ocean DMS over the full range of oceanographic conditions. The simple, robust design and relatively low cost of the instrument are intended to facilitate use in process studies and surveys, with potential for long-term deployment on research vessels, ships of opportunity, and large buoys.

Modification of polytetrafluoroethylene porous membranes by electron beam initiated surface grafting of binary monomers

Polytetrafluoroethylene (PTFE) porous membranes were pre-irradiated by electron beam in vacuum. And then the hydrophilic sulfonate groups were introduced by the single step grafting method with binary monomer solution of acrylic acid (AAc) and sodium 4-styrenesulfonate (SSS). The effect of monomer concentration and irradiation dose on degree of grafting, the surface morphological and chemical changes after grafting reaction, as well as the surface hydrophilicity of the modified membrane, were investigated. The surface chemical change was determined by Fourier transform infrared attenuated total reflection spectroscopy (FTIR-ATR) and X-ray photoelectron spectroscopy (XPS). Morphological changes on the film surface were described using field emitting scanning electron microscopy (SEM). The surface hydrophilicity of the modified film was characterized through water contact angle measurement. The degree of grafting changed with different AAc contents in binary monomers and irradiation doses, and the water contact angle of the film surface reduced significantly when compared with the original one. These results indicated that the grafted polymer layer introduced hydrophilic groups to PTFE membrane and improved the hydrophilicity of the porous membrane.

A proton-exchange membrane prepared by the radiation grafting of styrene and silica into polytetrafluoroethylene films

A polytetrafluoroethylene (PTFE) based organic–inorganic hybrid proton-exchange membrane was prepared from simultaneous radiation grafting of styrene (St) into porous PTFE membrane with the in situ sol–gel reaction of tetraethoxysilane (TEOS) followed by sulfonation in fuming sulfonic acid. The effect of radiation on the sol–gel reaction was studied. The results show that radiation promotes the sol–gel reaction with the help of St at room temperature. Incorporated silica gel helps to produce higher degree of grafting (DOG). SEM analysis was conducted to confirm that the inorganic silicon oxide was introduced to produce hybrid membrane in this work. The proton conductivity of membrane evaluated using electrochemical impedance spectroscopy is much higher (14.3×10 −2 S cm −1) than that of Nafion ® 117 at temperature of 80 °C with acceptable water uptake 51 wt%.

Novel styrene/N-phenylmaleimidealternating copolymers with pendant sulfonimide acid groups for polymer electrolyte fuel cell applications

Alternating terpolymers, si-PPMSs, are synthesized from styrene, N-phenylmaleimide (PMI), and PMI with a sulfonimide acid group for polymer electrolyte fuel cell applications. The ion-exchange capacity (IEC) of si-PPMSs can be easily controlled by changing the feed ratios of the comonomers, and the resulting si-PPMSs (IEC = 0.89–1.19 meq g−1) exhibit good thermal and chemical stabilities. In order to fabricate mechanically strong membranes with a high IEC, polymer gels consisting of substituted PMI, styrene, and divinylbenzene are prepared using porous polytetrafluoroethylene membranes. A gel-filling membrane with an IEC of 1.70 meq g−1, si-PPMS gel, exhibits a proton conductivity of ca. 1.0 × 10−2 S cm−1 at 50 °C under 95% relative humidity; its proton conductivity is comparable to that of Nafion 112. A H2/O2fuel cell comprising a si-PPMS gel membrane could be operated at 1 A cm−2 and an open circuit voltage of 0.93 V.

Sulfonated polyimide/PTFE reinforced membrane for PEMFCs

A sulfonated polyimide (SPI)/PTFE reinforced membrane was synthesized by impregnating PTFE (porous polytetrafluoroethylene) membrane with a SPI/DMSO solution. The resulting composite membrane was mechanically durable and quite thin relative to traditional perfluorosulfonated ionomer membranes (PFSI). We expect the PTFE to restrict the swelling and dimensional change of the SPI when it is immersed into water. And the reinforcement with PTFE can increase the hydrolysis stability of the SPI due to the low swelling and low dimensional change. From ex-situ testing and a short term fuel cell “life” test, we conclude that the PTFE reinforced sulfonated polyimide had a higher hydrolytic stability than pure sulfonated polyimide. The thin SPI/PTFE membrane showed comparable fuel cell performance with the commercial NRE-212 membrane with H 2/O 2 at 80 °C under fully humidified conditions. The chemically modified membrane with Nafion layer showed good stability in a 120 h fuel cell test.

In situ gas generation for micro gas analysis system

This manuscript describes an easy, simple and small system for gas generation. The aim of this work was to establish gas generation for on-site checking or on-site calibration of a micro gas analysis system, μGAS. The new technology, μGAS, achieves real-time measurement of trace level gases in the field. To make the measurement more reliable and convenient, a small gas generation system has been developed. Source reagent solution and generator solution are made to flow by micropumps, mixed in a miniature coil, and then introduced into a microchannel gas desorber. The gas desorber is comprised of a honeycomb-shaped microchannel covered with a thin porous polytetrafluoroethylene membrane. A good generation factor is obtained due to the wide vaporization area and thin solution layer of the microchannel desorber. Generation of H 2S, SO 2, CH 3SH and NH 3 gases were examined. Concentrations of the gases are easily controlled by the source reagent concentration and the solution flow rates. At 100 μL min −1 flow rates for both the source and generator solutions, 30 ppbv to 2 ppmv concentrations are formed with a gas flow rate of 200 mL min −1. The gas concentration is proportional to the source concentration. The gas generation can be performed only when needed. The gas generation system is combined with μGAS for on-site calibration.

Electrochemical synthesis of N 2O 5 by oxidation of N 2O 4 in nitric acid with PTFE membrane

Electrochemical synthesis of dinitrogen pentoxide (N 2O 5) by oxidation of dinitrogen tetroxide (N 2O 4) in a plate-and-frame electrolyzer was investigated. As the separator, different porous polytetrafluoroethylene (PTFE) membranes were tested in this process and the effects of hydrophilicity and of hydrophobicity on the electrolysis were discussed. The transport of N 2O 4 and water from catholyte to anolyte through membrane occurred in the electrolysis, especially at the end of the electrolysis. The water transport had a much more effect on the electrolysis than that of the N 2O 4 diffusion. The hydrophobic PTFE membranes had better performance on control of water transport from catholyte to anolyte than that of the hydrophilic ones. Hydrophobicity can increase the chemical yield of N 2O 5. The membranes with a low hydrophobic surface were preferred. All the hydrophobic PTFE membranes with low resistance have the specific energy of 1.1–1.5 kWh kg −1 N 2O 5. The current efficiency of 67.3–80.2% and chemical yield of 58.9–60.9% were achieved in production of N 2O 5. The technique of replacing the catholyte with fresh nitric acid can minimize the transport of N 2O 4 and water to a great extent, it can further improve the chemical yield and reduce the specific energy.

Investigation of an Ozone Membrane Contactor System

Ozone mass transfer rates were determined for nine expanded porous Teflon membranes that had different pore size, thickness, and pore volume, a nonporous Teflon membrane, and a PVDF membrane. The mass transfer coefficient was 7.6 ± 0.5 × 10−5 m/s at Re of 2000 for all membranes tested even though pore sizes ranged from 0.07 to 6 μm and thickness from 0.076 to 0.25 mm. Mass transfer increased with liquid side Reynolds number. Therefore, it is likely that ozone mass transfer is liquid phase controlling and not membrane limited. For a hypothetical case of 4000 m3/d and 2 mg/L ozone transferred, plate and frame membrane and hollow fiber contactors are approximately one and two orders of magnitude smaller, respectively, than fine-bubble diffusers.

Limited penetration of anticancer drugs to cells in solid tumors: A neglected and modifiable cause of drug resistance

9563 Background: Regardless of the drug sensitivity of tumor cells, treatment of solid tumors will only be effective if drugs delivered in the blood penetrate tissue to achieve adequate concentration in the tumor microenvironment. Here we report studies of the penetration of anticancer drugs through tumor tissue in a model system and in solid tumors of mice. Methods: Tumor cells were grown on collagen-coated porous teflon membranes to form multicellular layers (MCL) up to 200μm thick, that resemble tissue in solid tumors. We studied the time-dependent penetration through MCL of several anticancer drugs. Immunohistochemistry was used to study distribution of fluorescent doxorubicin in murine tumors and human tumor xenografts in relation to blood vessels (stained with anti CD-31) and hypoxic regions (identified by uptake of EF-5). Results: Penetration of drugs through MCL is slow compared with that through the teflon membrane, especially for the weak bases doxorubicin and mitoxantrone (<10% penetration relative to the teflon membrane alone). Weak bases are sequestered in acidic endosomes, and strategies to raise endosomal pH leads to less drug uptake into cells without loss of cytotoxicity and improved penetration of tissue. Modification of extracellular matrix also influences penetration in MCL. Doxorubicin has very poor penetration in solid tumors of mice, with a decrease in mean concentration to ∼50% of that in blood over about 3 cell layers. The concentration of doxorubicin remains at background in large areas of viable tumor tissue following a single i.v. injection into mice. Conclusions: Limited distribution of drugs from blood vessels in solid tumors is an important and neglected cause of drug resistance. Several strategies might be used to improve drug penetration and hence therapeutic index. Supported by a grant from CIHR. No significant financial relationships to disclose.

Membrane-introduced infrared spectroscopic chemical sensing method for the detection of volatile organic compounds in aqueous solutions

A novel membrane-introduced infrared (IR) chemical sensing method has been developed for the detection of volatile organic compounds (VOCs) in aqueous solutions. In this method, a porous Teflon membrane was used to eliminate the problems associated with conventional IR spectroscopic sensing methods. The porous Teflon membrane was sealed below an IR spectroscopic sensing element pre-coated with a hydrophobic film and a two-channel flow cell configuration was established. In this configuration, the aqueous sample was allowed to pass through the lower channel and the VOCs that penetrated through the membrane to the upper channel were detected by the IR sensor. In this manner, the performance of the sampling at the headspace was improved while the problems caused by the presence of water were eliminated. Meanwhile, using a purging channel allowed the sensing element to be regenerated rapidly and enabled automation of the detection process. The parameters that influenced the analytical signals were studied, such as the sampling flow rate, the pH and ionic strength of the sample solutions, the effect of the volatilities of the VOCs, and the regeneration efficiency of the sensing element. The results indicated that the analytical signals were insensitive to the sampling flow rate and to the pH and ionic strength of the sample solutions. The results obtained from the detection of seven different volatile compounds indicated that this method is highly suitable for the detection of organic compounds that have vapor pressures >1 Torr and that it is potentially usable for organic compounds that have vapor pressures between 20 mTorr and 1 Torr. The regression analysis of the standard curves indicated that a regression coefficient (R(2)) > 0.99 was obtainable in the concentration range from 1 to 100 microg mL(-1). The detection limits for the tested compounds were around a few hundred ng mL(-1).

Influence of charging conditions on permeability for the membrane of porous polytetrafluoroethylene (PTFE) film electret

In this paper, the influence of charging conditions on permeability of porous PTFE membranes is studied by constant voltage corona charging at room and elevated temperatures and by measuring the flow rate in water when porous PTFE electret films are used as a filter membrane. We found that charging field and charging temperature strongly affect the flow rate of water, but charging time does not influence the flow rate markedly. The structure of porous PTFE film, investigated by a scanning electron microscope, is important for understanding the influence of charging conditions on the membrane permeability. The increase of the ratio of the bulk charge density to the surface charge density of the porous electret films is performed by thermal treatment during charging. Such porous films may be employed as electret filter membranes with high efficiency to purify dielectric liquids.

Differential electrochemical mass spectrometry

Differential electrochemical mass spectrometry (DEMS) can be used not only to identify products or intermediates of continuous faradaic reactions, but also to characterize submonolayer amounts of adsorbates on polycrystalline and single crystal electrode surfaces by means of their desorption, because of its high sensitivity. One possibility to achieve this is to oxidize a carbonaceous species to CO(2), which is quantitatively detected in the mass spectrometer. Many adsorbates can also be desorbed at certain potentials as such, or as the hydrogenated product, allowing a more direct characterization of the adsorbate. In some cases, a nonreactive desorption can be induced by displacement with a second adsorbate, yielding additional information. Interfacing an electrochemical cell to a mass spectrometer via a porous Teflon membrane can be achieved with a variety of cells. These will be described together with their specific advantages and characteristics.

Chemical Sensors – from Molecules, Complex Mixtures to Cells – Supramolecular Imprinting Strategies

Methods of modern chemistry are a powerful tool in generating functional materials suitable as chemically sensitive layers to be combined with a variety of transducer principles. Molecular pits in polymers are formed by molecular imprinting, by suitable double-imprinting e.g. PAHs can be detected down to the sub-μg/l level. The resulting selectivity patterns depend both on the polymerization temperature and the template/mononomer composition. Organic contaminants in water can be either directly assessed in liquid phase or separated from the matrix by a porous Teflon membrane. Thus the detection limits can be reduced to the ppm-level due to the a much lower noise level in gaseous phase. Even complex processes such as engine oil degradation can be followed by suitably imprinted polymers. Pits on the nm- to μm scale are reached by surface templating polymers with microorganisms. The resulting layers show reversible, antibody-like interactions and thus are optimal sensor layers. The successful on-line detection of tobacco mosaic viruses (TMV) can be achieved by these surface imprinted layers.

Coating of TiO 2 photocatalysts on super-hydrophobic porous teflon membrane by an ion assisted deposition method and their self-cleaning performance

By means of an ion assisted deposition method, a TiO 2 photocatalyst was prepared at relatively lower temperature on porous Teflon sheets (PTS) that are good candidates for the coating materials with super-hydrophobic surfaces. UV light irradiation of TiO 2 photocatalyst on PTS led to the photocatalytic degradation of organic pollutants (self-cleaning), which wear off the water-repellent property of the original PTS surface. The PTS surface loading of a small amount of TiO 2 photocatalyst can keep the super-hydrophobic properties of PTS for a long time because of the photocatalytic degradation of the accumulated pollutants.