Porous Polytetrafluoroethylene Research Articles

Measurement of bidirectional transmittance distribution function in the visible and near-infrared spectral range

This work characterizes a facility for bidirectional transmittance distribution function (BTDF) measurements in the visible and near-infrared (NIR) wavelength range. The facility includes an absolute reference gonioreflectometer, with an extended capability for BTDF measurements, and a commercial instrument, Cary 7000, using a goniometer extension, Universal Measurement Accessory. The facility characterization includes measurements of two quasi-Lambertian diffusers for their BTDF. The diffuser samples include a piece of porous polytetrafluoroethylene (PTFE) and a piece of fused synthetic silica, HOD-500. The samples are measured for their spectral BTDF in the wavelength range from 450 nm to 1650 nm in 50 nm steps, and in the viewing zenith angle range from −35° to 35° in 5° steps. Measurements are performed in-plane, using an incident zenith angle of 0°, while rotating the samples around their surface normal from 0° to 180° in 90° steps. Rotation of the sample serves the dual purpose of checking the sample rotational symmetry in azimuth angles and for averaging the measurement results. The characterization results show that both samples exhibit Lambertian characteristics across the visible and NIR wavelength range. Furthermore, both samples show a smooth increase in their spectral BTDF as a function of wavelength. Notably, the PTFE sample demonstrates a steeper slope in its spectral BTDF and a higher signal above 650 nm. The facility capability for measurements of spectral BTDF is validated by a rigorous uncertainty analysis and by comparing the difference in measurement results between the absolute gonioreflectometer and the commercial instrument. Characterization results indicate that the absolute reference gonioreflectometer has a standard uncertainty ranging from 0.29% to 0.42%, dependent on the BTDF measurement wavelength. Experimental results show that the devices of the facility deviate in their BTDF within their combined expanded uncertainty, affirming the capability and reliability of the facility for BTDF measurements.

Tribological properties of oil-impregnated porous PTFE composites using CA as a novel pore-forming agent

PurposeThis paper aims to prepare an oil-impregnated porous polytetrafluoroethylene (PTFE) composite with advanced tribological properties using citric acid as a novel pore-forming agent.Design/methodology/approachCitric acid (CA) was used to form pores in PTFE, and then oil-impregnated PTFE composites were prepared. The pore-forming efficiency of CA was evaluated. The possible mechanism of lubrication was proposed according to the tribological properties.FindingsThe results show CA is an efficient pore-forming agent and completely removed, and the porosity of the PTFE increases with the increase of the CA content. The oil-impregnated porous PTFE exhibits an excellent tribological performance, an increased wear resistance of 77.29% was realized in comparison with neat PTFE.Originality/valueThis study enhances understanding of the lubrication mechanism of oil-impregnated porous polymers and guides for their tribological applications.

Ultra–thin ePTFE–enforced electrolyte and electrolyte–electrode(s) assembly for high–performance solid–state lithium batteries

Challenges including low stability, excessive thickness, a low ionic conductivity of current solid–state electrolytes, and large interfacial resistance in solid–state lithium batteries (SSLBs) hinder their application. Herein, an ultra–thin electrolyte (∼20 μm) was prepared by using expanded porous polytetrafluoroethylene (ePTFE) as a framework and filling the pores with a hybrid electrolyte; it exhibited a high stability, mechanical strength, flexibility, and ionic conductivity (0.27 mS cm−1). A new mechanism for fast lithium-ion conduction in the composite electrolyte was creatively proposed, whereby the interface orients and concentrates lithium ions to accelerate ion transport. An electrolyte–electrode(s) assembly (EEA) was developed by directly spraying active material(s) with highly dispersed electrolytes on the electrolyte. EEA–based copper– and aluminum–free SSLBs with or without a low-dose liquid electrolyte achieved an excellent performance at room temperature. Furthermore, EEA–series–connected pouch batteries demonstrated high voltage, safety, and performance, making our ultra–thin electrolyte and EEA promising for the development of SSLBs.

Rational design of polymer-based insulating scaffolds for high-capacity lithium metal batteries

Lithium metal is a promising anode material for next-generation high-energy–density secondary batteries. However, the uncontrolled growth of Li dendrites leads to infinite volume expansion and poor cycling stability. Herein, we propose a designable insulating polydopamine (PDA)-coated porous polytetrafluoroethylene (PTFE) scaffold. A porous PTFE (pPTFE) scaffold with micron-sized pores was fabricated, which provided bottom-up Li deposition owing to its insulating nature. Furthermore, the PDA-coated porous PTFE (PDA-pPTFE) scaffold provided internal space for Li growth and homogenized the Li-ion flux with abundant polar functional groups in the PDA, enabling “bottom-up” Li deposition within the scaffold without dendrite growth. This uniquely designed scaffold demonstrated excellent performance in half and symmetric cells with a small voltage hysteresis and dendrite-free Li plating. Moreover, when coupled with high-loading NCM cathodes (∼4 mA h cm−2), the PDA-pPTFE-based full cells exhibited stable cycling and rate performance, even with a low NP ratio of 1.0 at a rate of 1/3C, and exhibited a high energy density of 801 W h L−1. These results indicated the potential of the PDA-pPTFE scaffold as an anode material for highly stable next-generation rechargeable batteries.

Unveiling zirconium phytate-heteropolyacids-ionic liquids membranes for PEM fuel cells applications up to 150 °C

In the context of escalating energy demands and the pressing issues of climate change, fuel cells emerge as a pivotal, economically feasible, and environmentally sound renewable energy alternative. This study highlights the importance of fuel cells, specifically focusing on high-temperature and Nafion-free membranes. Membranes composed of zirconium phytate, silicotungstic acid, polyethylene glycol, and ionic liquids employing porous polytetrafluoroethylene polymer for support are reported. Investigating varying ratios of silicotungstic acid, polyethylene glycol, and ionic liquids, electrochemical spectroscopy revealed heightened proton conductivity upon ionic liquids integration. Initially, the unmodified zirconium phytate membrane demonstrated a conductivity of 6.65 × 10−4 S/cm, escalating tenfold (2.23 × 10−3 S/cm) with silicotungstic acid addition. Further enhancements, such as incorporating polyethylene glycol, led to an increase in the conductivity to 3.81 × 10−2 S/cm. The maximum conductivity value obtained in this work (0.1 S/cm), comparable to Nafion, was achieved with 5.86 wt% of the 1-Hexyl-3-methylimidazolium tricyanomethanide. Testing at elevated temperatures up to 150 °C revealed a drop in conductivity by two orders of magnitude (10−3 S/cm), highlighting their remarkable conductive properties. Additionally, water uptake analysis demonstrated the membranes' ability to retain more than 60 wt% water molecules within their matrix. Furthermore, thermogravimetric analysis revealed the thermal stability of membranes at high temperatures up to 600 °C. These findings strongly indicate that these synthesized membranes possess considerable potential for high temperature proton exchange membrane fuel cell applications.

Secondary roughness effect of surface microstructures on secondary electron emission and multipactor threshold for PTFE-filled and PI-filled single ridge waveguides

Secondary electron yield (SEY) is a dominant factor in determining the multipactor threshold. In this study, we analyzed the secondary roughness effect of surface microstructures for plastic dielectric on SEY reduction and multipactor mitigation. A single ridge waveguide (SRW) operating in Ku-band, filled with polytetrafluoroethylene (PTFE) or polyimide (PI), was designed with a dielectric–metal multipactor gap. By employing a femtosecond laser, periodic microstructures were fabricated on PTFE and PI surfaces to suppress SEY. The SEY peak values of PTFE and PI decreased from 2.05 to 1.40 and 1.37 to 1.07 by the porous surface. The surface morphologies and cross-sectional images of the porous PTFE and PI demonstrated the existence of secondary roughness structures. Via simulation, we obtained multipactor thresholds of 8496 W, 12 374 W, and 9397 W for the SRWs filled with untreated PTFE surface, ideal porous surface (without secondary roughness), and real porous surface (with secondary roughness). Similar works were implemented for the PI-filled SRWs, resulting in simulated multipactor thresholds of 7640 W, 11 327 W, and 9433 W. The results indicate that the multipactor effect may not be effectively suppressed under the influence of secondary roughness structures such as plastic velvet and foam. Besides, simulation works indicated that the radio frequency electric field could extract secondary electrons from the microstructures, weakening the mitigation effect of microstructures on multipactor. The impact of surface charging on electron motion was also analyzed by considering energy distribution. It was suggested that the surface microstructures of plastic dielectrics lead to a decrease in the surface charge density and the electrostatic field strength, weakening the self-extinguishing effect and lowering the multipactor threshold. This study provides an in-depth analysis of the effect of secondary roughness on SEY and multipactor for organic dielectrics, which makes significant sense for the further investigation of dielectric multipactor.

Robust poly(p‐phenylene oxide) anion exchange membranes reinforced with pore‐filling technique for water electrolysis

AbstractMechanical robustness and durability are crucial for anion exchange membranes to guarantee the longevity and consistent performance of AEM water electrolysis (AEMWE) systems. In this study, a composite membrane based on the quaternized poly(p‐phenylene oxide) (QPPO)/polytetrafluoroethylene (PTFE) was developed. This membrane was fabricated by enhancing the QPPO‐based AEM through a pore‐filling technique within a porous PTFE structure. The tensile strength of the composite membrane was increased significantly from 16.5 to 31 MPa. The conductivity of the composite membrane was 6.25 mScm−1 lower than 30 mScm−1 of the QPPO‐based membrane at 20°C, resulting from the low volume fraction of QPPO in the composite membrane. At 40% RH, the net change mass of the composite membrane is 1.59%, much lower than that of QPPO‐based membrane (10.98%) at 40°C. The composite membrane demonstrated a significantly increased lifetime in the working electrolyzer (>200 h) compared with an otherwise identical electrolyzer assembled with a QPPO‐based membrane (50 h).

Superwetting membrane-based strategy for highly efficient separation of dimethyl carbonate and methanol

Dimethyl carbonate (DMC) produced through transesterification, which involves the reaction of methanol (MeOH) with a suitable ester, has been considered as an attractive route for industrial production. Although high-purity DMC can be obtained from DMC/MeOH mixture by energy-intensive extractive distillation or time-consuming pervaporation (PV), it is still challenging to produce pure DMC in an energy-saving and high-efficiency manner. Here we demonstrate an energy-economy yet efficient superwetting membrane (SWM)-based strategy to produce pure DMC by combining porous polytetrafluoroethylene (PTFE) as the solid membrane and eco-friendly water molecules as the liquid inductive agent. The relatively low polar DMC can rapidly and selectively permeate the nonpolar PTFE membrane by nonpolar interaction between PTFE and DMC. Meanwhile, the high polar water molecules generate strong hydration with MeOH, which makes the relatively high polar MeOH/H2O being blocked by the nonpolar PTFE membrane. The SWM system exhibits outstanding separation flux of 1090 L m−2 h−1, with DMC purity higher than 93 wt%. Furthermore, taking advantage of the easy assembly of this SWM with conventional PV, we can produce DMC with purity of 99.4 wt%, showing great potential in practical DMC production.

Effect of Asymmetrically Reinforced Membrane on Anion Exchange Membrane Fuel Cell

Anion Exchange Membrane Fuel Cells (AEMFCs) is promising for the generation of electric power from hydrogen, with the expected possible replacement of precious metal catalysts by Earth abundant ones.[1-2] Beyond the independent properties of core materials (AEM, anode and cathode catalysts), the water management during operation is key to achieving high power density, but also high longevity. Thin AEMs are critical to achieve high AEMFC power performance, as the back-diffusion of water from anode to cathode critically helps to mitigate anode flooding. [3] Due to the high swelling of hydrated AEMs, good mechanical durability of thin AEMs however typically requires the introduction of a reinforcement, often a porous polytetrafluoroethylene (PTFE) membrane filled with the anion exchange ionomer.Here, we investigated the structure of different commercial AEMs and their behavior in operating AEMFC. We identified that the position of the reinforced layer (PTFE or other) strongly differs from one type of AEM to another. In the case of strongly asymmetric through-plane position of the PTFE layer (Fig. 1a), the positioning of the PTFE reinforcement close to anode or to cathode has a significant impact on initial power performance (Fig. 1b). A better performance and improved stability was observed with the PTFE layer close to the anode, suggesting that the asymmetric structure can improve the water management in such configuration. The presentation will discuss the results obtained on different commercial AEMs, and whether the asymmetric structure of AEM can be combined with PTFE hydrophobized anodes for even improved performance. The effect of the reinforcement position on the water management was also studied operando by two techniques. With high energy X-ray diffraction technique on an AEMFC under current load, the water distribution profile across the MEA thickness could be obtained from phase deconvolution analysis. With the use of relative humidity sensors at the outlet of anode and cathode of a regular AEMFC setup, [4] the water balance at a given current load could be established and compared for the two different positionings of reinforced AEM.The results shed light on the importance of identifying the position of PTFE reinforcement in commercial or in-house AEM for AEMFC application, with potential implications also for AEM electrolyzers or water-CO2 co-electrolyzers.

Quantitative Analysis of CO2 Evolution in an Alkaline Electrolyte Solution By Differential Electrochemical Mass Spectroscopy

CO2 is involved in various main and side reactions of electrochemical energy devices, such as carbon corrosion reactions and alcohol oxidation reactions. Differential electrochemical mass spectroscopy (DEMS) has been intensively applied in acidic electrolyte solutions to analyze these reactions. DEMS is the in-situ electrochemical measurement technique to analyze volatile species with the mass spectrometer (MS). However, the applications of DEMS to alkaline electrolyte solutions have been limited due to the high solubility of CO2 in alkaline solutions. While "conventional DEMS cells," where porous thin-film working electrodes are formed onto polytetrafluoroethylene (PTFE) membrane interface, can quantitatively analyze CO2 that has not dissolved into the electrolyte yet [1], the working electrode materials are limited to those that can be deposited on porous PTFE membrane as porous thin-films. Recently, Möller et al. have developed the DEMS system, which can detect CO2 from general planer electrodes coated by catalyst powders by combining a neutralizer and "dual thin-layer flow cell" [2]. However, due to the relatively low detection limit, quantitative analysis of evolved CO2 has not been accomplished. In this study, we attempt to use high surface area electrodes to enhance the MS signal of CO2 to enable quantitative analysis of evolved CO2. To suppress the in-plane reaction distribution in the flow cell, we integrated an anion exchange membrane into the cell and arranged the counter electrode opposing the working electrode [3] (Fig. 1 (a)).CO-stripping voltammetry was performed to evaluate the CO2 detectability of the constructed DEMS system. The DEMS cell was composed of a commercial Pt/C electrode as the working electrode, a commercial Hg/HgO electrode as the reference electrode, a Pt mesh as the reference electrode, 1 mol dm–3 KOH aq as the electrolyte solution, and 1 mol dm–3 H2SO4 aq as the neutralizer. Figure 1 (b) shows the CO-stripping voltammogram and corresponding MS signal of CO2 (m/z = 44). MS signal of CO2 accompanied by the anodic CO oxidation current is clearly observed from 0.6 to 1.2 V vs. RHE. The calibration constant, which correlates the MS signal of CO2 to partial current for CO2 evolution reaction, is successfully obtained as 2.2 × 10–10, which shows that the DEMS system established in this study can quantitatively analyze CO2. Applications to the carbon corrosion reactions are also presented at the site.

Application of Nanoconfinement Technology for Highly Effective Monitoring of Chemical Exposure During Military Service.

There is myriad of volatile compounds to which military personnel are exposed that can potentially have negative effects on their health. Military service occurs in a broad array of environments so it is difficult to predict the hazardous compounds to which the personnel might be exposed. XploSafe is developing passive diffusive samplers to facilitate the sampling and quantification of a wide range of chemical vapor exposures that personnel may be exposed to in the workplace. Passive diffusive samplers were constructed by filling porous Teflon tubes with OSU-6, a nanoporous silica sorbent, to produce sampler tokens. Three of these tokens were placed within a badge to fabricate passive samplers. Absorption experiments were performed to determine linear exposure regimes, sampling rates, and limits of quantification for 11 compounds, representing 8 chemical classes. The sampling rates were determined for 11 compounds representing 8 chemical classes. The measured linear ranges for the studied compounds are sufficiently large to allow effective sampling for 8 hours or longer. Accurate dosimetry is possible even with exposure times of days or weeks. The samplers were able to detect the presence of five airborne compounds in a paint booth of a military contractor located in Bristow, Oklahoma, and determine their average exposure concentrations. OSU-6 based sampler badges were able to detect the presence and quantify the average exposures of five airborne compounds in a paint booth of a military contractor located in Bristow, Oklahoma. Experiments show that these samplers can adsorb and quantify a broad array of different volatile organic compounds whose high sampling rates coupled with high capacity provide both sensitivity and the ability to quantify over a large range of exposures. This technology can meet the requirements for personal samplers to create Individual Longitudinal Exposure Record for each military person.

Robust superwetting polytetrafluoroethylene membranes with interlayer-bridged inorganic nanocoating for efficient oil/water separation

Treating oily wastewater is of great importance and urgency worldwide. The superhydrophilic and underwater superoleophobic (SUS) membrane is an effective alternative to realize such a goal. However, most SUS membranes are vulnerable in harsh environments, such as strong acidic/alkaline solutions or physical abrasion, resulting in a limited lifespan. In this work, a robust SUS membrane was developed by depositing in situ a TiO2 nanocoating onto the polytetrafluoroethylene (PTFE) porous membrane with (3-[(perfluorohexyl sulfonyl) amino] propyltriethoxy silane) (PFSS) as an intermediate layer. In the preparation process, the fibrils and nodes of the PTFE membrane were integrally enclosed with the chemical networks generated by hydrolysis and self-condensation of the PFSS. Then, the nano-TiO2 was in situ bonded with the sulfonyl amide group of the PFSS via bidentate coordination. As a result, an ultrathin and continuous nano-TiO2 coating (∼20 nm) was created, and the coating covered throughout the porous PTFE matrix. The resultant PTFE membranes demonstrated typical SUS characteristics, while their pore structure was almost unchanged. The PTFE SUS membranes exhibited a high emulsion permeance (up to 18,700 L m–2h−1 bar−1) with a separation efficiency above 99.3%. Attributed to the soldering effect of the PFSS between TiO2 nanoparticles and the PTFE membrane, the developed SUS membranes exhibited excellent stability against strong acid/alkali washing and hydraulic shearing, all of which outperformed the majority of current SUS membranes.

Janus membranes with simultaneous flux enhancement and fouling/wetting resistance prepared by a modified interfacial polymerization process for membrane distillation

Conventional membrane distillation (MD) membranes are hydrophobic and challenged by severe membrane fouling and wetting. Current surface modification strategies for anti-fouling and anti-wetting purposes, usually complex and time-consuming, often compromise the MD flux. Herein, we propose a modified interfacial polymerization (mIP) approach to fabricate Janus membranes with rapid and robust MD performance. In the mIP process, a dry hydrophobic substrate is first immersed in an oil-phase monomer solution and then in contact with an aqueous monomer solution to trigger the mIP reaction. The as-fabricated Janus membrane (e.g., IP2@PTFE) comprised an ultrathin, underwater oleophobic, and defect-free polyamide (PA) layer and a porous polytetrafluoroethylene (PTFE) substrate. Compared with the unmodified PTFE membrane, the vacuum MD flux of the IP2@PTFE membrane held a 177.4 % increase when tackling a NaCl solution (3.5 wt%) at 60 °C. When the NaCl solution contained sodium dodecyl sulfate (SDS) surfactant or/and mineral oil, the IP2@PTFE membrane exhibited fouling and wetting resistance simultaneously; conversely, severe oil fouling and quick SDS-induced wetting occurred on the pristine PTFE membrane. The mIP process does not require any pretreatment of the hydrophobic substrate, so it is facile and scalable. We believe that this study will facilitate the design of robust MD membranes.

Miniaturized liquid extraction cartridge with a functional porous polytetrafluoroethylene membrane for the determination of formaldehyde in gaseous samples

Miniaturized liquid extraction cartridge with a functional porous polytetrafluoroethylene membrane for the determination of formaldehyde in gaseous samples

Sulfonated poly(p-phenylene)-based ionomer/PTFE composite membrane with enhanced performance and durability for energy conversion devices

Proton exchange membranes (PEMs) have to be fabricated as thin as possible to minimize the ohmic loss in the cell voltage of proton exchange membrane fuel cells (PEMFCs) and water electrolyzers (PEMWEs). Additionally, the dimensional and mechanical stabilities of the PEMs must be maintained because they are critical for prolonging the cell lifespan in energy conversion devices that are used in moist environments. Herein, a sulfonated poly(p-phenylene)-based (SPP) multiblock ionomer is impregnated into a porous polytetrafluoroethylene (PTFE) substrate as a practical strategy for fabricating a mechanically robust and thin membrane. A five-layered structure is fabricated using two PTFE substrates as the composite membrane to increase the interfacial area between the SPP ionomer and PTFE; PTFE is treated with n-propyl alcohol to mediate the interfacial interactions between the two incompatible components. The composite membrane exhibits enhanced dimensional stability and mechanical properties compared with those of the pristine membrane owing to the SPP ionomer interlocking with PTFE. Regarding the electrochemical properties, the cell performance of the composite membrane displays a high current density of 1.52 A/cm2 at 0.5 V and 7.90 A/cm2 at 1.9 V for PEMFC and PEMWE, respectively; these densities are 32% and 16% greater, respectively, than that of Nafion212.

Optimization of Device Parameters for Back‐Contact Transparent Conductive Oxide–Less Dye‐Sensitized Solar Cells Fabrication

Transparent conductive oxide–less (TCO‐less) dye‐sensitized solar cell (DSSC) has been constructed and characterized employing mesoporous TiO2‐coated stainless‐steel mesh (S‐S‐mesh or Mesh) as a bendable photoanode and iodine‐based redox electrolyte. Efforts have been directed toward optimizing electronic parameters to enhance the power conversion efficiency (PCE) of TCO‐less DSSC to equalize its TCO‐based DSSC counterpart. It is found that protection of Mesh is essential for increasing the PCE of TCO‐less DSSCs employing iodine electrolyte as assured by suppressed reverse saturation current and better diode factor. The PCE of 5.6% is obtained with TCO‐less DSSC compared with TCO‐based DSSC with PCE of 6.09%. A bit of decrease in PCE with TCO‐less DSSC is due to larger resistance in TiO2/dye/electrolyte as well as within electrolyte as evident by electrochemical impedance spectroscopy (EIS) study owing to the Mesh having perforated holes and larger thickness of electrolyte absorbing sheet of the porous polytetrafluoroethylene film (35 μm) compared to TCO‐based DSSC without any barriers and lower electrolyte layer thickness of 25 μm.

Imidazole and imidazolium functionalized poly(vinyl chloride) blended polymer membranes reinforced by PTFE for vanadium redox flow batteries

A novel blended polymer membrane is prepared by a facile route for using as the diaphragm in vanadium redox flow batteries (VRFBs). The polymers polyvinylchloride (PVC) and polyvinylpyrrolidone (PVP) are first blended in a 1.2:1 mol ratio to give a PVP-PVC mixture, and the PVC in the mixture is then functionalized with 1-(3-aminopropyl)-imidazole (APIm). The functionalized polymers are impregnated into the porous polytetrafluoroethylene (PTFE) to fabricate membranes. The obtained membranes possess superior affinity to sulfuric acid mainly due to acid-base interactions between APIm groups and sulfuric acid molecules. The presence of hydrophobic PTFE restricts the deterioration of mechanical strength of membranes by doped acids. Moreover, the prepared membranes exhibit high oxidation stability and low vanadium permeability. The VRFB assembled with the proposed diaphragm displays energy efficiency above 82 % at a current density range of 20 to 120 mA cm−2. The membrane-based VRFB demonstrates stable performance after over 50 charge–discharge cycles.

Modeling of CO2 absorption in a membrane contactor containing 3-diethylaminopropylamine (DEAPA) solvent

Among the pollutants known as greenhouse gasses, carbon dioxide (CO2), although it is less toxic than the others, has by far the most significant amount of pollution in the earth's atmosphere. Also, it is one of the typical components of natural gas, which is removed due to the increase in fuel value and the adjustment of pipeline standards to prevent acid corrosion. There are various techniques for CO2 removal, among which membrane processes are a new and applied technology with many advantages in industrial separation. 3-diethylaminopropylamine (DEAPA) is a new amine absorbent with good interaction with CO2 molecules and increased absorption capacity, which shows good potential for CO2 separation. This study aims to investigate the performance potential of CO2 absorption by an aqueous solution of DEAPA as an absorbent in a hollow fiber membrane contactor (HFMC) with hydrophobic porous polytetrafluoroethylene (PTFE) fibers. A two-dimensional mathematical model was presented and solved based on the finite element method (FEM) to evaluate the CO2 removal efficiency. The effect of different parameters such as amine concentration, liquid and gas flow rate, liquid temperature, CO2 partial pressure, membrane tortuosity, number of hollow fibers, and packing density on CO2 absorption performance was investigated. The model results showed that increasing the gas flow rate and membrane tortuosity has a negative effect on CO2 removal. Also, increasing the amine concentration, packing density, the number of hollow fibers, DEAPA concentration, liquid temperature, and CO2 partial pressure improve the CO2 separation efficiency.

Developing a Novel Terahertz Fabry-Perot Microcavity Biosensor by Incorporating Porous Film for Yeast Sensing.

We present a novel terahertz (THz) Fabry-Perot (FP) microcavity biosensor that uses a porous polytetrafluoroethylene (PTFE) supporting film to improve microorganism detection. The THz FP microcavity confines and enhances fields in the middle of the cavity, where the target microbial film is placed with the aid of a PTFE film having a dielectric constant close to unity in the THz range. The resonant frequency shift increased linearly with increasing amount of yeasts, without showing saturation behavior under our experimental conditions. These results agree well with finite-difference time-domain (FDTD) simulations. The sensor's sensitivity was 11.7 GHz/μm, close to the optimal condition of 12.5 GHz/μm, when yeast was placed at the cavity's center, but no frequency shift was observed when the yeast was coated on the mirror side. We derived an explicit relation for the frequency shift as a function of the index, amount, and location of the substances that is consistent with the electric field distribution across the cavity. We also produced THz transmission images of yeast-coated PTFE, mapping the frequency shift of the FP resonance and revealing the spatial distribution of yeast.

Miniaturized liquid extraction cartridge with a functional porous polytetrafluoroethylene membrane for the determination of formaldehyde in gaseous samples

AbstractA new miniaturized liquid extraction cartridge equipped with a functional porous polytetrafluoroethylene membrane was developed for the determination of formaldehyde in gaseous samples. The functional polytetrafluoroethylene membrane allows gas to pass through while repelling both water‐based and organic‐based liquids. A derivatization reagent for formaldehyde, 2,4‐dinitrophenylhydrazine, was placed in the cartridge and gaseous samples are collected through the cartridge at 20 ml/min for 30 min. Formaldehyde in the gaseous sample is captured as the corresponding 2,4‐dinitrophenylhydrazine hydrazone, and an aliquot of the sample collection solution can be directly subjected to high‐performance liquid chromatographic analysis. The limit of quantification for the developed method was 5 ng/L formaldehyde in gas with a sampling volume of 600 ml. Proof‐of‐concept for formaldehyde determination in an aqueous sample was demonstrated using the developed cartridge in a purge‐and‐trap extraction setup.