Polytetrafluoroethylene Particles Research Articles

Dust proof properties of spinodal porous surfaces.

With an aim of dust proof in optical coating, contact force with spinodal porous surfaces was investigated by counting the number of particles after exposure to a practical circumstance and by directly measuring the contact forces with a probe of Au sphere using an atomic force microscope (AFM). The interaction between the oiled particles and the porous surface was also investigated on an antireflection coating using greases containing particles of polytetrafluoroethylene (PTFE). It was found that the porous structure played the role of adsorbing oil and lowering the contact force between the particles and the surface without deterioration of the antireflection. The contact force was treated based on the liquid bridges between the particles and the surface, and the contribution from the term of Laplace pressure is inferred to be lowered due to the reduced width of the silica skeletons.

Design and optimization of gradient wettability pore structure of adaptive PEM fuel cell cathode catalyst layer

The design of cathode catalyst layer (CL) is essential to improve the mass transfer capacity of proton exchange membrane (PEM) fuel cell and increase power density. In this work, cathode CL is divided into three sub-layers, and each sub-layer is added nano-particles with different wettability. The gradient CL with hydrophilic SiO2 particles at inner layer and hydrophobic polytetrafluoroethylene (PTFE) particles at outer layer significantly enhances the performance of membrane exchange assembly (MEA). Its performance is 895 mW/cm2@0.6 V, which is 24.1 %higher than CL without any particles (721 mW/cm2@ 0.6 V). Under operating conditions of high current density, high cathode humidity and high air stoichiometry, the gradient CL has only a little voltage loss. Through Electrochemical Impedance Spectroscopies (EIS) impedance analysis under high current density (1.8A/cm2), mass transfer resistance of gradient CL is 25.4 Ω, and is much smaller than the mass transfer resistance of the homogeneous CL of 35.1 Ω, which reflects the significant enhancement in mass transfer capacity of gradient CL. The gradient catalyst layer is suitable for a wider range of current density, humidity, and stoichiometry, but excessive cathode gas stoichiometry causes a decrease in performance, which is caused by excessive drainage capacity. In addition, 18 different gradient CLs are designed and manufactured, and the gradient CL with catalyst coated membrane (CCM) structure has the best performance. In gradient CL, increasing the capillary pressure difference between sublayers is the key to performance improvement. It is confirmed that the property of MEA with appropriate wettability gradient design can be significantly improved.

Reinforcement of Frictional Vibration Noise Reduction Properties of a Polymer Material by PTFE Particles.

The insufficient lubrication of the contact interface between moving parts can easily induce severe friction vibration and noise under extreme working conditions, which will threaten the service life and reliability of polymer moving components, including water-lubricated stern tube polymer bearings. Thermoplastic polyurethane (TPU) modified by polytetrafluoroethylene (PTFE) particles was developed. The effects of PTFE on the wear and vibration behaviors of modified TPU sliding against the ZCuSn10Zn2 ring-plates were investigated. The coefficients of friction (COFs), wear mass losses, wear morphologies, frictional vibration, and noise were analyzed synthetically. The results showed that a suitable mass content of PTFE reduced the COFs and wear mass losses of the TPU composites by more than 50% and 40%, respectively, while presenting an excellent friction reduction. The lower COFs of modified TPU showed a small fluctuation amplitude and eliminated vibration waveforms at high vibrational frequencies, which was useful for reducing frictional vibration and noise. The knowledge gained in this study is useful for a better understanding of the wear behaviors of polymer composites, as well as for the design a new polymer material with good self-lubricating and frictional vibration and noise reduction properties.

Spraying pressure-tuning for the fabrication of the tunable adhesion superhydrophobic coatings between Lotus effect and Petal effect and their anti-icing performance

The tunable adhesion behavior of superhydrophobic surfaces has received much attention due to its unique properties to control the wetting state of water droplets. Herein, we report a facile and scalable spraying pressure-tuning method to control surface morphology by adjusting the spraying pressure to fabricate the tunable adhesion superhydrophobic coating (TASC). The superhydrophobic suspension prepared by fluorinated epoxy resin and polytetrafluoroethylene particles is sprayed on the glass substrate by altering the spraying pressure between 0.25 bar and 2.0 bar to control surface morphology, line profile, and surface roughness of TASCs. The water contact angles of TASCs are greater than 150°, while the water sliding angles of these surfaces are found from 2.6° (Lotus effect) to 180° (Petal effect) with the decrease of spraying pressure, which are attributed to the transformation of the wetting state on their surface from Cassie-Baxter state to Cassie impregnating state caused by the change of line profile and the decrease of surface roughness. We have proved that TASCs with different spraying pressure can be used in the droplet transportation, selection, and microreaction platform. Furthermore, the anti-icing performance of TASCs with different surface morphology and roughness was investigated by the freezing time and the ice adhesion strength. TASC-2.0 exhibited excellent anti-icing performance with freezing time at 392 s and the ice adhesion strength at 51 kPa than TASC-0.25 exhibited relatively flat surface, which is attributed to the air pocket captured by rough structure to reduce the solid/liquid contact area and has great potential for anti-icing applications.

Micro/nano-structured electrospun membranes with superhydrophobic and photodynamic antibacterial performances

Bacterial infection has been a major cause of morbidity and mortality worldwide, which gives rise to numerous disasters in humans. General superhydrophobic surface displays remarkable bacterial repellence, but generally lack essential antimicrobial activity, and is hard to get a totally bacteria-free surface. In this study, we report a micro/nano-structured electrospun membrane with both superhydrophobic and photodynamic antibacterial performances. Through a facile and convenient electrospinning method, a series of composite membranes consisting of poly(vinylidene) fluoride (PVDF) nano-sized fiber, micro-sized polytetrafluoroethylene (PTFE) particles and photosensitizer Chlorin e6 (Ce6) are prepared, which can be transformed into superhydrophobic membranes after a surface fluorination. The optimized superhydrophobic membrane demonstrates remarkable bacterial repellence with very low bacterial adhesion (~3.6% for S. aureus and ~4.3% for E. coil), and also possesses effective photodynamic antimicrobial activities, under vis-light illumination, even can get a totally bacterial-free surface against S. aureus. Additionally, the membrane also showed no obvious hemolysis as well as low-level cytotoxicity. This work may inspire the development of novel antibacterial membrane surfaces with both bacterial repellence and bactericidal performances for high-efficient and safe bacterial disinfection.

Recyclable fluorous-tag assisted two-directional oligosaccharide synthesis enabled by interrupted Pummerer reaction mediated glycosylation.

Herein, we report a novel fluorous-tag assisted two-directional oligosaccharide assembly strategy, which maintained the high coupling efficiency of solution-phase synthesis and featured the advantage of an easy purification process comparable to solid-phase synthesis. A well-designed fluorous tag was decorated on the latent anomeric leaving group in interrupted Pummerer reaction mediated (IPRm) glycosylation. The high efficiency of the in-solution phase glycosylation and the unique affinity of the fluorous tag towards polytetrafluoroethylene (PTFE) particles allowed flexible assembly from the reducing end to the non-reducing end and fast purification by PTFE-assisted filtration. Moreover, the fluorous-tagged latent anomeric leaving group could be activated by oxidation and cleaved by IPRm glycosylation, thus enabling the elongation of the carbohydrate chain from the non-reducing end to the reducing end as well as the recovery of the fluorous tag. The present two-directional synthetic strategy is used to assemble the repeating unit of Streptococcus pneumoniae type 14 capsular polysaccharide.

Water Repellent Modified Polyester Fabric Based Triboelectric Nanogenerator for Harvesting Human Mechanical Energies

Wearable triboelectric nanogenerators (TENGs) for converting human mechanical energies into electricity are being investigated widely, because of their potentially diverse applications that come from wearable power supplied to multifunctional self-powered sensing. However, external influences, such as water or high humidity, seriously degrade the electrical output of TENGs. Therefore, a simple method was implemented for fabricating a water repellent fabric-based TENG for harvesting human mechanical energies. Polytetrafluoroethylene (PTFE) or SiO2 modified by trichloro(octadecyl)silane (OTS) were sprayed onto a polyester (PET) fabric surface to increase hydrophobicity. The PTFE and SiO2/OTS coated polyester fabrics exhibited excellent water repellency with a high-water contact angle of ∼144° and ∼153°, respectively. The surface morphology of the coated fabrics showed roughness with a granular structure, which was responsible for air entrapment that prevented water from penetrating the fabric. Furthermore, electrical output of conventional PET fabric-based TENG was found to improve with the deposition of PTFE particles on the fabric surface. By pairing the PTFE coated fabric with aluminum (Al) tape, in order to fabricate TENG, the device generated a maximum voltage of 10.2 V and short-circuit current of 0.20 µA, with a power output of 0.23 W/cm2, which is 14 times greater than that of SiO2/OTS coated fabric-based TENG. The process for achieving water repellent fabric is simple, and the coating materials are available. Thus, a water repellent fabric-based TENG is promising for large-scale production of wearable harvesters from power supplied to multifunctional self-powered sensing.

Continuously harvesting energy from water and wind by pulsed triboelectric nanogenerator for self-powered seawater electrolysis

Due to deterioration of the environment and energy crises, exploring clean and renewable energy from ambient surroundings has become one of the most urgent concerns in our society. Herein, we report a pulsed cylindrical triboelectric nanogenerator (TENG) based on polytetrafluoroethylene (PTFE) particles. The as-designed TENG can harvest low-frequency mechanical energies from wind and water and convert them into electricity at low cost and high efficiency, which can not only lighten 475 green LED lamps in series, but also can be suitable for driving seawater electrolysis for hydrogen production. The constructed TENG based on the Maxwell’s displacement current provides a model for further development of self-powered seawater electrolysis for hydrogen production.Graphical Abstract [Display omitted]

Effect of particle characteristics on particle collision behaviors and heat transfer performance in a down-flow circulating fluidized bed evaporator

The effects of particle characteristics on particle collision behaviors and heat transfer are investigated based on standard deviation and kurtosis analysis in a down-flow circulating fluidized bed evaporator. Results show particle addition can enhance heat transfer for all types of particles. The maximum enhancing factor reaches 33.0% within the experimental range by adding polytetrafluoroethylene particles at ε=1.5%, V=5.16 m3/h and q = 8 kW/m2. For different types of particles, with increased amount of added particles, enhancing factor initially increases and then decreases; standard deviation increases but kurtosis decreases. With increased circulation flow rate, standard deviation and enhancing factor tend to increase but kurtosis decrease. With increased heat flux, standard deviation tends to increase but kurtosis and enhancing factor decrease. Density, sedimentation velocity and surface wetting performance obviously influence particle collision and heat transfer performance. High standard deviation and low kurtosis are beneficial to heat transfer.

Enhancing rate capability of graphite anodes for lithium-ion batteries by pore-structuring

For the development of high-performance lithium-ion batteries (LIBs), numerous studies on 3-dimensionalized electrode structures have been conducted to improve the ionic diffusion, rate performance, and electrolyte wetting ability. Due to the decrease in ionic polarization, structured electrodes show much higher capacity retention compared to typical electrodes, especially at high current rates. In this study, pore-structured graphite (Gr) electrodes were synthesized using pore-formation agent particles (polytetrafluoroethylene (PTFE)), which possess a unique thermal unzipping property. After the heat treatment, the PTFE particles were depolymerized to form micro-sized pores. The effect of the 3-dimensionalized electrode structure on the electrochemical properties was investigated in detail. As a result, it was observed that the rate capability and cycle life of pore-structured Gr electrodes enhanced owing to their improved physical properties, such as wetting ability and shortened ionic diffusion pathways. Because our approach does not require changes in the existing electrode chemistry and slurry process, it is one of the most cost-effective and applicable ways to improve fast charging capability.

Micro-nano-sized polytetrafluoroethylene (teflon) particles as a model of plastic pollution detection in living organisms.

Micro- and nano-sized particles of polytetrafluoroethylene (PTFE) were used as model (reference) particles to study the biological effects of plastic pollution. Since the PTFE molecule contains fluorine, considered as an "atomic marker" sharply distinguishing it from other common plastics, micro- and nano-particles of PTFE have a specific crystalline structure and are, therefore, well identified by the methods of polarized light microscopy (POL), Raman microspectroscopy (micro-Raman), and energy-dispersive spectroscopy (EDS). Examples of PTFE particles detection in hemolimph of the cockroach Blatella germanica, in hemolimph of the larva and in faecal pellets of imago of a fly Lucilia sp., in the stomach and hingat of brine shrimp Artemia salina, and in association with cell wall of green unicellular alga Chlorococcus sp. are provided. The presented results strongly suggest that PTFE particles can be detected and identified in the biological medium using the method of "atomic markers", polarization microscopy and Raman spectroscopy.

Combination of nano-particles of graphite and PTFE in the right amount for synergism as anti-wear and extreme pressure additive in oil

Solid lubricants (SLs) are known to enhance the tribo-performance of oils significantly. Polytetrafluoroethylene (PTFE) particles have proved as an excellent extreme-pressure additive (EPA) but not as so good anti-wear additive (AWA). In contrast, the graphite nano-particles (NPs) are known as very good AWA but not so promising EPA. In this context, graphite and PTFE particles with different shapes (graphite-laminar and PTFE- spherical) and sizes (graphite- 60–120 nm and PTFE- 11–13 μm) were used in combination in different amounts for exploring possible synergism as AWA and EPA. A series of oils based on Group III (Gr III) with polyisobutylene succinimide (PIBSI) dispersant (1 wt%) along with an increasing amount of graphite NPs (0%–4%) and a simultaneous decrease in PTFE NPs (4%–0%) was prepared. The tribo-performance of oils was evaluated on Four ball tester for EP (weld-load) and anti-wear performance. Formulations were characterized for density, viscosity, and viscosity index. Also, the stability of oils was monitored through visual observation, and it was more than two months. Combo-oils showed improvement in anti-wear (AW) performance up to 54% for the concentration of 2 wt% each. For AW, synergism was observed, while for extreme pressure (EP) property, PTFE particles in isolation proved best, showing almost 350% improvement for group III oil. The inclusion of graphite particles step by step deteriorated the performance. The SEM (Scanning electron microscopy) and EDAX (Energy-dispersive X-ray) were used to analyze worn surfaces of ball and film formation mechanism.

Polymer Pressure‐Sensitive Adhesive with A Temperature‐Insensitive Loss Factor Operating Under Water and Oil

AbstractLoss factor tan δ determines the viscoelasticity of a material. Higher or lower loss factor tanδ (>1 or <1) suggests a viscous or elastic material. Most polymer pressure‐sensitive adhesives (PSAs) possess a limited operational temperature range (near room temperature), above which the PSAs trend to be more viscous (un‐crosslinked) or more elastic (crosslinked), and below which PSAs become more elastic. These properties are unfavorable for PSA operation. Herein, an underwater PSA possessing short hydrophobic side chains and weak hydrogen bond interactions are described. Proper modulus and stable loss factor close to 1 contributes to an efficient adhesion underwater over a temperature range of 0–100 °C. Moreover, by introducing Teflon particles, the adhesion can be operated under silicon oil from room temperature to 150 °C due to the formation of a drainage surface structure and its temperature insensitivity.

Aqueous dispersion and tuning surface charges of polytetrafluoroethylene particles by bioinspired polydopamine-polyethyleneimine coating via one-step method.

We propose a surface modification of poorly dispersive polytetrafluoroethylene (PTFE) particles via bioinspired polydopamine–polyethyleneimine (PDA–PEI) which conferred PTFE particles a uniform dispersion in aqueous medium. With increasing dopamine concentration in the reaction solution, dispersity of PTFE particles improved and the surface charges of particles changed from negative to positive due to an increase of surface coverage of PDA–PEI layers. Simplicity of the method here outlines an attractive route for surface modification of inert surfaces useful for large-scale applications.

Failure behaviors of 3D braided composites with defects in different locations under low-velocity impact compression

This paper aims to investigate the effects of the impurity defects in different locations on the transverse compressive behaviors of three-dimensional (3D) braided carbon fiber/epoxy composites under low-velocity impact. The composites with defects in different locations were prepared by placing polytetrafluoroethylene particles at the bottom surface, corner and center parts, respectively. The compression test was implemented with the drop-weight impact method. The failure morphologies were characterized using high-speed photography and micro computed tomography (Micro-CT). A mesoscale finite element model considering the defect was developed to enhance the physical understanding of the compression process. It is found that defects located at the corner zone and the central zone have a greater impact on the compression behavior of the 3D braided composite than the defect located at the bottom surface part. The defects at the corner and center zones reduce the compressive strength of the composite, increase the failure area, and cause severe damage to both the yarn and resin. In addition, the defect causes local stress concentration on the surrounding yarns. The defects in different locations cannot change the main shear failure mode of the 3D braided composite. It is shown that great attention should be given during the manufacturing or detection process to avoid such a deterioration effect of defects located in those zones on composite strength.

Nonionic surfactant stabilized polytetrafluoroethylene dispersion: Effect of molecular structure and topology

Polytetrafluoroethylene (PTFE) is a kind of fluoropolymer with many critical applications. Nonionic surfactant stabilized concentrated PTFE aqueous dispersions are widely used to prepare corresponding products via dipping, spraying, spinning, or film casting, as these surfactants exert a negligible effect on the properties of the products. Although many nonionic surfactants have been used to stabilize PTFE dispersions in industry, the effects of molecular structure and topology are not well-documented; thus, currently, there is no basis for selecting or designing suitable novel surfactants to enhance dispersion stability. In this work, five nonionic surfactants with different topological structures including Tween 20, Tween 60, Tween 80, Brij L23, and Brij O20, were used to prepare concentrated PTFE dispersions. The variation of particle morphology before and after concentration was examined by scanning electron microscopy, and the static stability of the dispersions was quantitatively and objectively characterized using a Turbiscan analyzer based on multiple light scattering. Then the effect of surfactant molecular structure and topology on dispersion stability was discussed. We found that, after the enrichment process, the PTFE microspheres were tightly packed, and some were deformed. Brij surfactants which bears a linear hydrophilic oxyethylene (EO) chain can form a thicker hydration layer on the surface of PTFE particles than those of Tween surfactants which contains a branched hydrophilic EO chain. Accordingly, PTFE dispersions with Brij surfactants show better static stability. Moreover, in comparison with the saturated hydrophobic tail, the unsaturated hydrophobic chain is more flexible, so it can adhere to the surface of PTFE particles better, improving the stability. In addition, the increase of surfactant concentration contributes to the increase of micelles density and viscosity of the bulk dispersion, which can also enhance the stability. These findings are beneficial to design or choose suitable surfactants for high stability and high-quality concentrated PTFE dispersions.

Magnetorheological Characterization of PTFE-Based Grease With MoS2 Additive at Different Temperatures

Thermorheological characterizations of magnetorheological (MR) grease thickened with polytetrafluoroethylene (PTFE) and molybdenum disulphide (MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) used as an additive for two different greases prepared with 50% (MRG50) and 70% (MRG70) weight fractions of spherical carbonyl iron (CI) particles, respectively, are presented. The magnetic properties and glass transition temperature of prepared MR greases (MRGs) have been measured using vibrating sample magnetometer (VSM) and differential scanning calorimetry (DSC), respectively. The MR properties are investigated at different temperatures ranging from 25 °C to 65 °C at magnetic fields ranging from 0 to 0.75 T under rotational and oscillatory sweep tests using a magnetorheometer. It is observed that for MRG70, the shear stress and apparent viscosity increase with increasing temperature. This is explained based on the formation of monolayers of MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> as it interacts with MRG and the effect of thermal conductivity on magnetorheology. Yield stress of PTFE-based MRG has been shown to increase with temperature and magnetic field. Formation of PTFE particle clusters decreasing the localized heat dissipation has been explained to be the reason for this. With increasing magnetic field strength, the flow properties show an increasing trend. ON-state storage and loss modulus are studied to understand the effect of temperature and magnetic field on the viscoelasticity of PTFE-based MRG.

The Effect of Polytetrafluoroethylene (PTFE) Particles on Microstructural and Tribological Properties of Electroless Ni-P+PTFE Duplex Coatings Developed for Geothermal Applications

The selection of electroless nickel-phosphorus plating (ENP) has been inclined towards their properties and advantages with complex geometry applications. These properties include coating uniformity, low surface roughness, low wettability, high hardness, lubricity, and corrosion- and wear-resistance. Materials used in geothermal environments are exposed to harsh conditions such as high loads, temperature, and corrosive fluids, causing corrosion, scaling, erosion and wear of components. To improve the corrosion- and wear-resistance and anti-scaling properties of materials for geothermal environment, a ENP duplex coating with PTFE nanoparticles was developed and deposited on mild steel within the H2020 EU Geo-Coat project. ENP thin adhesive layer and ENP+PTFE top functional layer form the duplex structure of the coating. The objective of this study was to test the mechanical and tribological properties of the developed ENP-PTFE coatings with varying PTFE content. The microstructural, mechanical and tribological properties of the as-deposited coating with increasing PTFE content in the top functional layer in the order: ENP1, ENP2 and ENP3 were evaluated. The results showed maximum wear protection of the substrates at the lowest load; however, increasing load and sliding cycles increased the wear rates, and 79% increased lubrication was recorded for the ENP2 duplex coating. The wear performance of ENP3 greatly improved with a wear resistance of 8.3 × 104 m/mm3 compared to 6.9 × 104 m/mm3 for ENP2 and 2.1 × 104 m/mm3 for ENP1. The results are applicable in developing low friction, hydrophobic or wear-resistive surfaces for geothermal application.

Characterization and Determination of the Biocompatibility of Porous Polytetrafluoroethylene Membranes Fabricated via Electrospinning

The structure and properties of polytetrafluoroethylene (PTFE) polymeric membranes obtained by electrospinning from a suspension of PTFE in a solution of polyvinyl alcohol (PVA) with subsequent thermal treatment were presented. The effect of the PTFE suspension ratio in spinning solutions on the morphology, crystal structure, chemical composition, strength, and cytotoxicity of the formed PTFE membranes was evaluated. We found that a decrease in the PTFE suspension content in spinning solutions leads to a decrease in the number of defects in the membrane fibers, which increasing the strength and elongation. Membranes made from spinning solutions with a lower content of PTFE suspension have a higher degree of crystallinity and a more perfect crystal structure. It has been suggested that the products of PVA destruction during the heat treatment of PTFE/PVA membranes are capable of plasticizing effects on PTFE particles, improving the strength of PTFE membranes. The membranes after thermal treatment were not cytotoxic regardless of the PTFE suspension content in the spinning solutions. High biocompatibility of membranes was established during implantation into soft tissues.

Effect of Hot Rolling on the Intrinsic Properties of Aluminium-Titanium Bonded by PTFE/ C -Cyanoacrylate

The concern of this study shows the effect of hot rolling on the properties of a composite sheet prepared from aluminium bonded to titanium metals sandwiching PTFE (Du Pont)/graphite emulsion in perfluoro kerosene. The metals were soaked in hot oxygenated water and dried at 80 °C for 5 - 10 minutes to create a thin film of oxide. The metals were bonded with cyanoacrylate blended to the polymer emulsion that applied to the oxidized surface of the clean metals. Two coated surfaces sandwich the polytetrafluoroethylene (PTFE)/graphite emulsion followed by ‎hot-rolling. The rolling process was matched at 500- 560 °C (≈ 150 °C, over the melting point of the PTFE) under a pressure of 150-200 KPa. The obtained composite sheet was annealed at 550 °C to remove any residual stresses. Results revealed that upon cooling, the mix microphase would separate with the OH radicals on the metal surface and the CF displaced away. The temperature and time of cyanoacrylate application enhanced the extent of adhesion to create a homogeneous composite metal sheet. The effect of the hot rolling conditions was ascribed to the PTFE underactivity and incompatibility. Rolling imparts squeezing of the metals and changes the intrinsic properties. Linear thermal expansion coefficient of the composite sheet confirms partial diffusion of the soft metal in the harder one across the adhesive. The applied technique deforms the PTFE particles without inhibiting the adhesion strength of the cyanoacrylate. The prepared sheet has physical properties that would be suitable for bailiwick and structural ‎application.