Conventional Polytetrafluoroethylene Research Articles

Friction Characteristics and Lubrication Properties of Spherical Hinge Structure of Swivel Bridge

A spherical hinge structure is a key swivel bridge element that must be considered when evaluating friction characteristics and lubrication properties to meet the rotation requirement. Polytetrafluoroethylene (PTFE)-based spherical hinge sliders and lubrication coating have been employed for over 20 years, but with the growing tonnage of swivel bridge construction, their capacity to accommodate the required lubrication properties can be exceeded. In this manuscript, the optimal friction coefficient of the spherical hinge is obtained through the finite element analysis method. Four lubrication coatings and four spherical hinge sliders are prepared and tested through a self-developed rotation friction coefficient test, four-ball machine test, dynamic shear rheological test, and compression and shear performance test to evaluate the lubrication and friction properties of the spherical hinge structure. The results of the finite element analysis show that the optimum rotation friction coefficient of the spherical hinge structure is 0.031–1.131. The test results illustrate that the friction coefficient, wear scar diameter, maximum non-seize load, phase transition point, and thixotropic ring area of graphene lubrication coating are 0.065, 0.79 mm, 426 N, 14.6%, and 64,878 Pa/s. The graphene lubrication coating has different degrees of improvement compared with conventional polytetrafluoroethylene lubrication coating, showing more excellent lubrication properties, bearing capacity, thixotropy, and structural strength. Compressive and shear tests demonstrate that polyether ether ketone (PEEK) has good compressive and shear mechanical properties. The maximum compressive stress of PEEK is 87.7% higher than conventional PTFE, and the shear strength of PEEK is 6.07 times higher than that of PTFE. The research results can provide significantly greater wear resistance and a lower friction coefficient of the spherical hinge structure, leading to lower traction energy consumption and ensuring smooth and precise bridge rotation.

Characterization of Catalyst Layer Using Gas Diffusion Electrode Half-Cell System for High Temperature Polymer Electrolyte Membrane Fuel Cell

High-temperature polymer electrolyte membrane fuel cell (HT-PEMFC) is being developed for the heavy-duty vehicle which requires high power density and operation under extreme conditions. Conventional HT-PEMFC using phosphoric acid (PA) immersed PBI membranes and polytetrafluoroethylene (PTFE) binder faced issues such as unstable durability and low performance of membrane electrode assembly (MEA) due to PA leakage and uneven distribution within the catalyst layer.In recent years, ion-pair membranes and ionomers for high temperatures have been developed, which can reduce PA leakage in MEA and improve ionic conduction within the catalyst layer. Incorporation of a new material into the MEA requires further research to enhance electrode design, catalyst utilization, and performance for the appropriate ionomer, as this material exhibits different characteristics from the conventional PTFE binder.In this study, various gas diffusion electrode (GDE) was fabricated with the new ionomer, and GDE half-cell setups were introduced for rapid and efficient characterization of performance in the oxygen reduction reaction. This system serves as an intermediate step between rotating disk electrodes and single cells, providing a powerful tool for quickly screening and evaluating GDEs using small amounts of catalyst. Recent publications from Wilkinson [1] and Gasteiger [2] groups reviewed this new system, proposed new measurement protocols, and suggested improvements. Accordingly, GDE half-cell setups are designed to simulate HT-PEMFC operating conditions at 150 ℃ temperature with 85 wt.% PA electrolyte.Electrochemical characteristics were evaluated using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) following the protocols in previous papers with GDE half-cell. Resistance values obtained through EIS were further differentiated by peaks and frequency-based responses through the distribution of relaxation times transformation. Performance comparison between GDEs was carried out by measuring the voltage at 0.2 A/cm² and peak power density at 150 ℃, simulating a single cell-like environment. GDEs were fabricated with variables such as Pt loading, thickness, and porosity. And their physical properties were confirmed through mercury intrusion porosimetry and scanning electron microscopy. Ultimately, the study elucidated the correlation between the electrochemical data and physical properties.

Polymethylhydrosiloxane-modified gas-diffusion cathode for more efficient and durable H2O2 electrosynthesis in the context of water treatment

On-site H2O2 electrosynthesis via two-electron oxygen reduction reaction (ORR) is attracting great interest for water treatment. The use of carbon black-based gas-diffusion electrodes (GDEs) is especially appealing, but their activity, selectivity and long-term stability must be improved. Here, a facile GDEs modification strategy using trace polymethylhydrosiloxane (PMHS) allowed reaching a outstanding H2O2 production, outperforming the conventional polytetrafluoroethylene (PTFE)-GDE (1874.8 vs 1087.4 mg L−1 at 360 min). The superhydrophobicity conferred by PMHS endowed the catalytic layer with high faradaic efficiencies (76.2%−89.7%) during long-term operation for 60 h. The electrochemical tests confirmed the high activity and selectivity of the PMHS-modified GDE. Moreover, the efficient degradation of several micropollutants by the electro-Fenton process demonstrated the great potential of the new GDE. An in-depth understanding of the roles of PMHS functional groups is provided from DFT calculations: the −CH3 groups contribute to form a superhydrophobic interface, whereas Si-H and as-formed Si-O-C sites modulate the coordination environment of active carbon centers.

Colored reflectors to improve coincidence timing resolution of BGO-based time-of-flight PET detectors

Time-of-flight (TOF) positron emission tomography (PET) detectors improve the signal-to-noise ratio of PET images by limiting the position of the generation of two 511 keV gamma-rays in space using the arrival time difference between the two photons. Unfortunately, bismuth germanate (BGO), widely used in conventional PET detectors, was limited as a TOF PET scintillator due to the relatively slow decay time of the scintillation photons. However, prompt Cerenkov light in BGO has been identified in addition to scintillation photons. Using Cerenkov photons for timing has significantly improved the coincidence timing resolution (CTR) of BGO. Based on this, further research on improving the CTR for a BGO-based TOF PET system is being actively conducted. Wrapping materials for BGO pixels have primarily employed white reflectors to most efficiently collect scintillation light. White reflectors have customarily been used as reflectors for BGO pixels even after Cerenkov light began to be utilized for timing calculations in pixel-level experiments. However, when the arrival-time differences of the two 511 keV annihilations photons were measured with pure Cerenkov radiators, painting the lateral sides of the radiators black can improve CTR by suppressing the reflection of Cerenkov photons. The use of BGO for TOF PET detectors requires simultaneously minimizing scintillation loss for good energy information and suppressing reflected Cerenkov photons for better timing performance. Thus, reflectors for BGO pixels should be optimized for better timing and energy performance. In this study, colored polytetrafluoroethylene (PTFE) tapes with discontinuous reflectance values at specific wavelengths were applied as a BGO reflector. We hypothesized that CTR could be enhanced by selectively suppressing reflected Cerenkov photons with an optimum colored reflector on the BGO pixel while minimizing scintillation photon loss. CTRs were investigated utilizing white and three colors (yellow, red, and green) PTFE tapes as a reflector. In addition, black-painted PTFE tape and enhanced specular reflector film were investigated as reference reflector materials. When 3 × 3 × 20 mm3 BGO pixels were wrapped with the yellow PTFE reflector, the CTR was significantly improved to 365 ± 5 ps from 403 ± 14 ps measured with the conventional white PTFE reflector. Adequate energy information was still obtained with only 4.1% degradation in light collection compared to the white reflector. Colored reflectors show the possibility to further improve CTR for BGO pixels with optimum reflectance design.

Wettability of polytetrafluoroethylene surfaces by plasma etching modifications.

Superhydrophobic surfaces (SHS) are attracting attention in many fields owing to their excellent advantages such as anti-freezing, corrosion prevention, and self-cleaning. However, to modify the surface structure, environmental pollution caused by complex processes and chemical treatment must be considered. In this study, the surface of polytetrafluoroethylene (PTFE) was plasma-treated using oxygen and argon plasma to change the surface structure without a complicated process. The PTFE surface was treated in two ways: plasma etching (PE) and reactive ion etching (RIE). The contact angle of the conventional PTFE surface was 113.8 ± 1.4°, but the contact angle of the manufactured surface was 152.3 ± 1.7° and 172.5 ± 1.2°. The chemical composition and physical structure of the samples produced were compared. The treated specimens had the same chemical composition as the specimen before treatment and exhibited differences in their surface structures. Therefore, it was determined that the change in the water repellency was due to the surface structure. After PE treatment, the specimen surface had a mountain range-like structure, and the RIE specimen had a more detailed structure than the PE specimen. The contact rate of water droplets decreased due to the difference in the structure of the specimen before and after treatment, and the increase in the surface contact angle was manifested. In order to confirm that the plasma treatment reduces surface energy, the shape of the liquid collision was observed using a high-speed camera, and the contact time was calculated to confirm water repellency. The contact time of the PE and RIE specimen was 24 milli-second (ms) and 18 ms, respectively. The high contact angle and low sliding angle of the RIE specimen made it easy to restore surface cleanliness in a self-cleaning experiment using graphite.

Robust polytetrafluoroethylene (PTFE) nanofibrous membrane achieved by shear-induced in-situ fibrillation for fast oil/water separation and solid removal in harsh solvents

Facing the severe pollution in modern industry, membrane separation is widely used to treat the wasted solvents owning to its low cost, high efficiency, and scalability. Microporous polytetrafluoroethylene (PTFE) membranes have been proved to be an ideal choice for waste separation owing to its excellent chemical resistance and low adhesion, but there are still challenges due to the poor processability of PTFE. Herein, we proposed an innovative shear-induced in-situ fibrillation methodology to prepare PTFE nanofibrous membranes, which successfully solve the dilemma between high porosity and ultrafine pore sizes of conventional microporous PTFE membranes. The achieved ultrafine nanofibrous membrane simultaneously has high porosity of 75%, fine pore size of 0.16 μm, and thin thickness of 10 μm. Consequently, the membrane not only shows outstanding mechanical properties with an ultrahigh tensile strength of up to 27.4 MPa, but also exhibits super-hydrophobicity/oleophilicity, chemical resistance, and anti-fouling behavior for fast separation or filtration in harsh solvents. For both oil/water emulsion and solid/liquid solution, a separation efficiency of more than 99.9% can be obtained, while permeate fluxes as high as 5197 L⋅m−2⋅h−1 and 36,929 L⋅m−2⋅h−1⋅bar−1 were achieved driven by gravity and pressure, respectively. This study opens promising avenues for the fabrication of robust and anticorrosive PTFE nanofibrous membranes with high separation efficiency by using a facile, green, and cost-effective in-situ fibrillation strategy.

Increasing in the heat resistance efficiency of filters using hydrophobic PVA/PEO/PTFE/SA nanofiber and PTFE nanoparticle composite

In this study, a conventional polytetrafluoroethylene (PTFE) foam-coated glass fabric filter (PG) was coated with a nanoparticle (NP)-decorated nanofiber (NF) filter to improve the surface and filtration performance and super water-repellent properties of the baghouse system used in industrial sites. Accordingly, a filter prepared by electrospinning PPPS and electrospraying PTFE NPs (PNP/PNF/PG filter) and a filter without PTFE NPs (PNF/PG filter) were manufactured using 0.005 L/m2 of the NF and a coated PTFE concentration of 0.002 L/m2. The samples were sintered at 320 °C, and a comparative analysis was performed on the samples. The surface of the PNP/PNF/PG filter had a higher surface roughness and contact angle than the PNF/PG filter, confirming that the hydrophobic surface characteristics of the existing PNF/PG filter were improved and maintained. Furthermore, based on the filter performance evaluation, the PNP/PNF/PG filter outperformed the PG and PNF/PG filters. In the particle range of 0.5 to 10.0 µm or more, the efficiency and QF were 98.79 % and 0.006. The PNP/PNF/PG filter improves filter performance while maintaining the surface characteristics of the PNF/PG filter.

Performance of proton exchange membrane fuel cells with microporous layer hydrophobized by polyphenylene sulfide at conventional temperature and cold start

Polyphenylene sulfide (PPS), a thermoplastic polymer with excellent chemical and thermal stability, has properties similar to those of polytetrafluoroethylene (PTFE) but is less expensive. In this study, the feasibility of using PPS to replace conventional PTFE as a hydrophobic agent for microporous layers (MPLs) in proton exchange membrane fuel cells (PEMFCs) is explored. First, PTFE-MPL and PPS-MPL with 30 wt% hydrophobic agent were prepared. The pore size, porosity, contact angle, and microstructure of the two MPL samples were measured and analyzed. Subsequently, PEMFCs with the two MPL samples were tested for their operational performance at a conventional temperature of 70 °C and cold-start capability at −10 °C. The performances of PTFE-MPL and PPS-MPL at conventional temperatures were similar, but PPS-MPL showed obvious advantages in cold-start performance. In addition, the operating performance of PEMFC at the conventional temperature and cold-start capability at −10 °C were investigated for PPS mass fractions of 10%, 20%, and 30% in MPL, and for PPS particle sizes of 10 and 30 μm. The results indicate that the optimal performance can be attained when the PPS particle size is 10 μm and the mass fraction is 20%.

Polytetrafluoroethylene fiber fabrication from the continuous melt-spinning process and its properties

Polytetrafluoroethylene (PTFE) has high thermal stability and chemical resistance, and hence is gaining great attention in the industrial field of high-performance filters, membranes, and medical applications. However, since PTFE possesses a narrow gap between melting (330°C) and decomposition temperatures (350°C), the melt-spinning process that is required to satisfy industrial needs for mass production has been limited. Here, perfluoro(propyl vinyl ether) (PPVE) was introduced to decrease the melting point of PTFE then fiber fabrication was performed with the melt-spinning process using a single-screw extruder, enabling the PTFE fiber to fabricate continuously. We selected an optimal melt-spinning condition and obtained PTFE fiber from the melt-processable PTFE/PPVE copolymer. The as-spun PTFE fiber showed low mechanical strength (0.90 g/denier or 89.1 MPa of tenacity). A post-thermal drawing process was performed to increase the mechanical strength of the PTFE as-spun. It demonstrated that the thermally drawn PTFE fiber showed higher mechanical strength (1.84 g/denier or 220.0 MPa of tenacity) due to the increased degree of crystallinity. Also, the other trial, thermal stabilization under N2, suggested as a future modification method to increase mechanical strength further, preventing thermal constriction of the PTFE fiber. The melt-spun and thermally drawn PTFE fibers were knitted and it was confirmed that the fiber has high chemical resistance and similar surface chemistry to conventional PTFE fibers. This study developed a method to enable a melt-processable PTFE fiber fabrication and opens up opportunities for mass production that is crucial in the industrial aspect.

Wear resistance effects of alumina and carbon nanoscale fillers in PFA, FEP, and HDPE polymers

Following numerous studies demonstrating the ability of nanostructured alpha-alumina filler to reduce the prohibitively high wear rate of polytetrafluoroethylene (PTFE) down to extremely small values (∼10−7 mm3/Nm) well below those of conventional PTFE micro-composites, alpha-alumina filler was also shown capable, in a couple recent studies, of imparting similar performance to another fluoropolymer, perfluoroalkoxy (PFA) copolymer, which otherwise was similarly lacking wear resistance in the unfilled state. In addition to duplicating such alpha-alumina performance in PFA, in this study such an extreme wear-reducing capability has also been demonstrated using nanocarbon powder, as an example representative of several other forms of nanoscale carbon filler that like alpha-alumina had been shown capable of providing extreme resistance to PTFE. Fluorinated ethylene propylene (FEP) copolymer, whose nanocomposites have not been tribologically explored previously, was thus more fully investigated here with not only alpha-alumina and nanocarbon, but also other nanotube (CNT) and mesoporous forms of nanoscale carbon fillers. In preliminary testing, only the alpha-alumina filler indicated an ability to impart its wear-reducing capability to FEP; a wear rate of ∼0.8 × 10−6 mm3/Nm was observed at 2 wt% alpha-alumina concentration. While this is an impressive reduction in wear rate, it is not quite as extreme a reduction as that observed in PTFE or PFA. The transport of the extreme wear resistance of nanocarbon powder in PTFE and PFA was even more partial and incomplete in FEP, with the ∼0.3 × 10−3 mm3/Nm unfilled FEP wear rate only reduced to ∼10−5 mm3/Nm, while the CNT and mesoporous carbon fillers were even less effective. Correspondingly, ATR-FTIR spectra from FEP wear surfaces displayed sizable peaks evident of the chelation of chemical interactions known to be associated with wear resistance for PTFE and PFA matrices only in the most wear-resistant alpha-alumina case and to a lesser extent for the nanocarbon. Finally, it is demonstrated that such fillers demonstrate such strongly beneficial effects only in polymers that otherwise lack wear resistance, and may actually be deleterious for polymers such as high density polyethylene (HDPE) already having some inherent wear resistance in their unfilled state.

Bifunctional Metal Meshes Acting as a Semipermeable Membrane and Electrode for Sensitive Electrochemical Determination of Volatile Compounds.

The monitoring of toxic inorganic gases and volatile organic compounds has brought the development of field-deployable, sensitive, and scalable sensors into focus. Here, we attempted to meet these requirements by using concurrently microhole-structured meshes as (i) a membrane for the gas diffusion extraction of an analyte from a donor sample and (ii) an electrode for the sensitive electrochemical determination of this target with the receptor electrolyte at rest. We used two types of meshes with complementary benefits, i.e., Ni mesh fabricated by robust, scalable, and well-established methods for manufacturing specific designs and stainless steel wire mesh (SSWM), which is commercially available at a low cost. The diffusion of gas (from a donor) was conducted in headspace mode, thus minimizing issues related to mesh fouling. When compared with the conventional polytetrafluoroethylene (PTFE) membrane, both the meshes (40 μm hole diameter) led to a higher amount of vapor collected into the electrolyte for subsequent detection. This inedited fashion produced a kind of reverse diffusion of the analyte dissolved into the electrolyte (receptor), i.e., from the electrode to bulk, which further enabled highly sensitive analyses. Using Ni mesh coated with Ni(OH)2 nanoparticles, the limit of detection reached for ethanol was 24-fold lower than the data attained by a platform with a PTFE membrane and placement of the electrode into electrolyte bulk. This system was applied in the determination of ethanol in complex samples related to the production of ethanol biofuel. It is noteworthy that a simple equation fitted by machine learning was able to provide accurate assays (accuracies from 97 to 102%) by overcoming matrix effect-related interferences on detection performance. Furthermore, preliminary measurements demonstrated the successful coating of the meshes with gold films as an alternative raw electrode material and the monitoring of HCl utilizing Au-coated SSWMs. These strategies extend the applicability of the platform that may help to develop valuable volatile sensing solutions.

Cr3C2-25NiCr Cermet Coating: Preparation, PTFE Sealant, Wear and Corrosion Resistances

In this study, Cr3C2-25NiCr cermet coatings were fabricated by atmospheric plasma spraying on 304 stainless steel substrate. Then, the coatings were sealed with a Polytetrafluoroethylene (PTFE) emulsion by using two methods: conventional impregnation and ultrasonic vibration. The phase composition, surface morphology, porosity, permeability of PTFE emulsion into the coating, wear and corrosion resistance of the coatings were investigated. The results showed that in the PTFE sealed coatings, besides carbide phases, a PTFE phase with an hexagonal crystal structure was formed. The PTFE covered the surface of the coating. The ultrasonic vibration method increased the permeability of the PTFE emulsion into the coating by more than 2 times that of the conventional impregnation method. The PTFE sealed coating by ultrasonic vibration method had a lower porosity, higher wear and corrosion resistances in 3.5 wt.% NaCl solution than the PTFE coating sealed by conventional impregnation method and PTFE unsealed coating.

Anisotropic Polytetrafluoroethylene Cardiovascular Conduits Spontaneously Expand in a Growing Lamb Model

Background Insertion of conduits from the right ventricle (RV) to the pulmonary artery (PA) is a commonly used technique for repair of congenital heart defects. The vast majority of infants and children will require reoperation and/or re-intervention to replace the conduit. Some children may require multiple reoperations, with the risk of death and morbidity increasing significantly with each subsequent operation. We evaluated the feasibility and performance of a relatively novel anisotropic conduit for cardiovascular repair in the growing lamb model. Materials and Methods Lambs were allocated into a control (n = 3) or test (n = 4, anisotropic) conduit group. Control conventional polytetrafluoroethylene (PTFE) conduits or test anisotropic expanded PTFE (ePTFE) based test conduits measuring 10–11 mm in diameter were sewn as interpositional grafts in the main pulmonary artery (MPA) and followed up to 6 months. Clinical and echocardiographic evaluations were performed monthly with hemodynamic and angiographic assessment at 3 and 6 months. Results Control conduits did not expand, all 3 animals developed one or more adverse events including tachypnea, ascites, inappetence, lethargy, and mortality due to severe right heart failure and significantly higher peak trans-conduit gradients (48.5 ± 5.1 p = 0.02). The test conduits spontaneously expanded up to 14.8 ± 0.8 mm in diameter, no adverse events were observed in any animals and trans-conduit gradients were significantly lower (27.0 ± 8.3, p = 0.02). Conclusions Anisotropic ePTFE conduits can be safely implanted in growing lambs with stable hemodynamics. This spontaneously expanding anisotropic conduit may represent a novel approach to congenital heart repairs that would avoid the need for reoperation or multiple operations.

Electrophoretic deposition of a supercapacitor electrode of activated carbon onto an indium-tin-oxide substrate using ethyl cellulose as a binder

A transparent energy storage device is an essential component for transparent electronics. The increasing demand for high-power devices stimulates the development of transparent supercapacitors with high power density. A transparent electrode for such supercapacitors can be assembled via the electrophoretic deposition of an active material powder with a binder onto a transparent substrate. The properties of the binder critically influence the electrochemical behavior and performance of the resulting electrode. Ethyl cellulose (EC) is known as an eco-friendly, transparent, flexible, and inexpensive material. Here, we fabricated an electrode film with EC binder via electrophoretic deposition on an indium tin oxide (ITO) substrate instead of using the conventional polytetrafluoroethylene (PTFE) binder. The assembled electrodes with EC and PTFE were compared to investigate the feasibility of EC as a binder from different perspectives, including homogeneity, wettability, electrochemical behavior, and mechanical stability. The EC enabled the formation of a homogeneous film composed of smaller particles and with a higher specific capacitance compared with films prepared with PTFE. The annealing improved the adhesion strength of the EC because of its glass transition; however, its hydrophobic nature limited utilization of the active material for charge storage. Subsequent electrochemical activation improved the wettability of the electrode, resulting in an increased capacitance of 60 F g−1. Furthermore, even with the lower wettability of EC compared with that of PTFE, better rate performance was possible with the EC electrode. The increased mechanical stability after the annealing process ensured an excellent cycle life of 95 % capacitance retention for 15,000 cycles.

Low temperature polytetrafluoroethylene (PTFE) coating improves the appearance of orthodontic wires without changing their mechanical properties.

A strong esthetic demand exists for white-colored rather than metallic-colored dental appliances. Polytetrafluoroethylene (PTFE), which is chemically stable with extremely low friction, is a suitable white-colored coating for dental appliances. In the conventional PTFE coating process, base materials are heated to approximately 400°C, which could change their mechanical properties. Examination of the PTFE-coating of stainless steel, nickel titanium (Ni-Ti), and β-titanium (Ti-Mo and Ti-Nb) revealed that the conventional 380°C coating, but not the newly developed low temperature coating at 200°C, reduced elasticity and bendability, and changed the crystal structure, especially in Ni-Ti and Ti-Nb wires. PTFE-coating at 200°C resulted in less discoloration, microbial adhesion, and friction against brackets, and higher tolerance of wear than did the conventional 380°C coating. These results suggest that low temperature PTFE coating is an excellent method for improving the metallic appearance of orthodontic wires without changing their mechanical properties.

Largely enhanced triboelectric nanogenerator for efficient harvesting of water wave energy by soft contacted structure

Triboelectric nanogenerator (TENG) is a new emerging and cost-effective technology for harvesting water wave energy because of its unmatchable performance in low frequency and randomly directed motions. Here, we report an approach that significantly increased the output power of spherical TENGs by optimizing both materials and structural design. Fabricated with an acrylic hollow sphere as its shell and a rolling flexible liquid/silicone as the soft core, the soft-contact spherical triboelectric nanogenerator (SS-TENG) presents up to 10-fold enhancement to the maximum output charge compared to that of a conventional Polytetrafluoroethylene (PTFE) based hard-contact one, which is resulted from the significantly increased contact area. Besides, the output is tunable through controlling the softness of the liquid/silicone core. Our finding provides a new optimization methodology for TENGs and enable its more promising usage in harvesting large-scale blue energy from water wave in oceans as well as feeble but ubiquitous wind energy.

Membrane Distillation Trial on Textile Wastewater Containing Surfactants Using Hydrophobic and Hydrophilic-Coated Polytetrafluoroethylene (PTFE) Membranes.

Treating wastewater from textile plants using membrane distillation (MD) has great potential due to the high-salinity wastes and availability of waste heat. However, textile wastewaters also contain surfactants, which compromise the essential hydrophobic feature of the membrane, causing membrane wetting. To address this wetting issue, a custom-made membrane consisting of a hydrophilic layer coated on hydrophobic polytetrafluoroethylene (PTFE) was tested on textile wastewater in a pilot MD setup, and compared with a conventional hydrophobic PTFE membrane. The test was carried out with a feed temperature of 60 °C, and a permeate temperature of 45 °C. The overall salt rejection of both membranes was very high, at 99%. However, the hydrophobic membrane showed rising permeate electrical conductivity, which was attributed to wetting of the membrane. Meanwhile, the hydrophilic-coated membrane showed continually declining electrical conductivity demonstrating an intact membrane that resisted wetting from the surfactants. Despite this positive result, the coated membrane did not survive a simple sodium hydroxide clean, which would be typically applied to a membrane process. This brief study showed the viability of membrane distillation membranes on real textile wastewaters containing surfactants using hydrophilic-coated hydrophobic PTFE, but the cleaning process required for membranes needs optimization.

How arteriovenous grafts could help to optimize vascular access management.

A one-size-fits-all approach to vascular access for dialysis may be prejudicial. Arteriovenous fistulae (AVF) have high primary failure, failure to mature rate, and late-stage complications making them unsuitable choice for many patients. Aging of population with chronic kidney disease (CKD) coupled with venous injury during CKD stages depletes suitable superficial veins for AVF creation. The National Institutes of Health consortium demonstrated the difficulty in attaining a functional AVF in hemodialysis patients. Recognition of flaws in AVF and the quest to reduce catheter use bring to the fore the benefits of arteriovenous grafts (AVG). Advances in catheter technologies, flow, care, and antibiotic locks have resulted in significant improvement in catheter-related infections. However, widespread recognition of catheter-related complications like central vein stenosis, metastatic infections, and exhaustion of venous access sites preclude their being a viable alternative to AVF, furthering the need to explore AVG as a substitute. Placement of "early cannulation" AVG is a catheter sparing option in patients who are likely to have inadequate fistula maturation. Advances in biohybrid technology and tissue-engineered grafts are providing a robust opportunity to develop biocompatible graft materials with minimal tissue reactivity and thrombogenicity. Xenografts (bovine carotid artery grafts) are proving to be comparable and, in many cases, better than conventional polytetrafluoroethylene material. Older age, dialysis dependence, and smaller vein size are related to the appropriateness of AVG creation. An individualized approach in selecting optimal upper extremity vascular access option using patient-specific factors while incorporating the benefits of an AVG would greatly aid in achieving low catheter usage in the dialysis population.

Characteristics of a non-volatile liquid propellant in liquid-fed ablative pulsed plasma thrusters

In the past several decades, the use of electric propulsion in spacecraft has experienced tremendous growth. With the increasing adoption of small satellites in the kilogram range, suitable propulsion systems will be necessary in the near future. Pulsed plasma thrusters (PPTs) were the first form of electric propulsion to be deployed in orbit, and are highly suitable for small satellites due to their inherent simplicity. However, their lifetime is limited by disadvantages such as carbon deposition leading to thruster failure, and complicated feeding systems required due to the conventional use of solid propellants (usually polytetrafluoroethylene (PTFE)). A promising alternative to solid propellants has recently emerged in the form of non-volatile liquids that are stable in vacuum. This study presents a broad comparison of the non-volatile liquid perfluoropolyether (PFPE) and solid PTFE as propellants on a PPT with a common design base. We show that liquid PFPE can be successfully used as a propellant, and exhibits similar plasma discharge properties to conventional solid PTFE, but with a mass bit that is an order of magnitude higher for an identical ablation area. We also demonstrate that the liquid PFPE propellant has exceptional resistance to carbon deposition, completely negating one of the major causes of thruster failure, while solid PTFE exhibited considerable carbon build-up. Energy dispersive X-ray spectroscopy was used to examine the elemental compositions of the surface deposition on the electrodes and the ablation area of the propellant (or PFPE encapsulator). The results show that based on its physical characteristics and behavior, non-volatile liquid PFPE is an extremely promising propellant for use in PPTs, with an extensive scope available for future research and development.

A reference material with close to Lambertian reflectance and fluorescence emission profiles

Fluorescent brightening agents are widely used in various industries to enhance the appearance of materials. The angular profiles of emission and reflectance of fluorescent surfaces have been shown to deviate from Lambertian behaviour, however, in industry and calibration facilities single geometry measurements are often used, which requires assumptions to be made on the angular distributions. In addition, the angular distribution of reflectance has been shown to deviate from that of fluorescence. In this work, it is shown that the angular distribution of reflectance is dependent on the excitation wavelength and the effect is explained by qualitative and quantitative models. These angular and spectral effects may cause measurement errors when single geometry bidirectional measurements are carried out. The angular distributions can be taken into account by using goniometrical measurements, which however, result in increased calibration time and cost. Alternatively, a reference material could be used where the angular dependencies are minimised. In this work, a novel material is presented which demonstrates more Lambertian emission and reflectance profiles than conventional polytetrafluoroethylene (PTFE) based materials and a smaller dependence of angular reflectance on the absorbance of the sample.