Polytetrafluoroethylene Particles Research Articles

Water-repelling, vapor-resisting, self-cleaning, oil–water-separating, water-purifying, antibacterial Hanji cellulose papers coated with Teflon and ZnO particles via supersonic spraying

Cellulose-based Korean mulberry paper, called Hanji, has been used as a functional material in heaters, supercapacitors, sensors, and light-emitting diodes because of its low weight, high mechanical strength, antibacterial activity, and eco-friendliness. Imparting water resistance property to these functional papers is critical to protect them against potential moisture-associated damage and to ensure their longevity. This study applied supersonic spraying technique to deposit superhydrophobic Teflon and antibacterial ZnO particles on Hanji. The results show that functionalized Hanji deposited with Teflon/ZnO exhibited water-repelling, anti-fogging, and antibacterial properties. Furthermore, the photoinduced water purification and self-cleaning features of functionalized Hanji has been demonstrated. Hanji enabled the passage of purple-colored hexane; however, blue-colored water could not permeate the Hanji filter, demonstrating the oil–water separation capability of Hanji.

Contact-electro-catalysis for Direct Synthesis of H2 O2 under Ambient Conditions.

Hydrogen peroxide (H2 O2 ) is an indispensable basic reagent in various industries, such as textile bleach, chemical synthesis, and environmental protection. However, it is challenging to prepare H2 O2 in a green, safe, simple and efficient way under ambient conditions. Here, we found that H2 O2 could be synthesized using a catalytic pathway only by contact charging a two-phase interface at room temperature and normal pressure. Particularly, under the action of mechanical force, electron transfer occurs during physical contact between polytetrafluoroethylene particles and deionized water/O2 interfaces, inducing the generation of reactive free radicals (⋅OH and ⋅O2 - ), and the free radicals could react to form H2 O2 , yielding as high as 313 μmol L-1 h-1 . In addition, the new reaction device could show long-term stable H2 O2 production. This work provides a novel method for the efficient preparation of H2 O2 , which may also stimulate further explorations on contact-electrification-induced chemistry process.

Contact‐electro‐catalysis for Direct Synthesis of H2O2 under Ambient Conditions

AbstractHydrogen peroxide (H2O2) is an indispensable basic reagent in various industries, such as textile bleach, chemical synthesis, and environmental protection. However, it is challenging to prepare H2O2 in a green, safe, simple and efficient way under ambient conditions. Here, we found that H2O2 could be synthesized using a catalytic pathway only by contact charging a two‐phase interface at room temperature and normal pressure. Particularly, under the action of mechanical force, electron transfer occurs during physical contact between polytetrafluoroethylene particles and deionized water/O2 interfaces, inducing the generation of reactive free radicals (⋅OH and ⋅O2− ), and the free radicals could react to form H2O2, yielding as high as 313 μmol L−1 h−1. In addition, the new reaction device could show long‐term stable H2O2 production. This work provides a novel method for the efficient preparation of H2O2, which may also stimulate further explorations on contact‐electrification‐induced chemistry process.

Sustainable charged composites with amphiphobic surfaces for harsh environment–tolerant non-contact mode triboelectric nanogenerators

In this work, the sustainable charged composites with amphiphobic surfaces are reported regarding harsh environment tolerance and robust contactless mode triboelectric nanogenerators (TENGs). SiO2 and polytetrafluoroethylene (PTFE) particles are well dispersed in thermoplastic polyurethane (TPU) and polydimethylsiloxane (PDMS), respectively. Both surfaces become very rough after a chemical etching method and the surface of PTFE-PDMS is fluorinated using a fluorinated alkylsilane, resulted in the formation of amphiphobic surfaces. This significantly enhances the environment tolerance of the contactless mode TENGs as well as the charge retention characteristics of the composites. As a practical non-contact mode application, a speed sensor fabricated using two composites can stably detect a low vehicle speed less than 3.75 km/h when exposed to high humidity (∼ 99%) and various chemical oils. Over 50% of initial output voltage are still generated after 2 weeks with no more decrease after 5 days, showing a 1.4 times slower charge decay rate, compared with the reference Ni-PTFE based TENG.

Direct observation of the wetting state of Cassie and Wenzel

In order to directly observe the solid–liquid-gas three-phase interface, we prepared the superhydrophobic coatings and high adhesion coatings respectively. The surface structure of the two coatings were observed by scanning electron microscopy. The superhydrophobic coating has good micro-nano structure, while the high adhesion coating has only micrometer structure due to the lack of nanometer Polytetrafluoroethylene particles. The wetting state of water droplets on the surface of the two coatings was observed by polarizing microscope and goniometer respectively. The results show that the water droplets in the superhydrophobic coating are in Cassie wetting state, while the water droplets in the high adhesion coating are in Wenzel wetting state. The experimental results provide direct observational evidence for the wetting state of Cassie and Wenzel.

Thermal Properties of Carbon Nanofiber Sheet for Thermal Interface Materials under High Temperature and Humidity

In this study, polyvinyl alcohol (PVA) - polytetrafluoroethylene (PTFE) - vapor grown carbon fiber (VGCF) sheets are fabricated as a new paper-like thermal interface material (TIM), which is a potential substitute for traditional TIMs. Two types of PVA-PTFE-VGCF sheets were fabricated by using 120 nm and 300 nm PTFE particles. The microstructure shows that the VGCFs were arranged in random directions inside the sheet and interconnected via the aggregate of PVA. 300 nm PTFE particles were well distributed within the sheet, while 120 nm PTFE particles aggregated partially and formed pores nearby. The fabricated sheets have a low thickness of 31.2 um and 28.2 um, and lightweight properties with a density of 0.79 × 106 g·m−3 and 0.91 × 106 g·m−3, respectively. With the addition of 300 nm PTFE particles, the fabricated sheet has higher thermal conductivities of 9.81 W·m−1·k−1 in the in-plane direction and 2.11 W·m−1·k−1 in the through-plane direction. In the high temperature and humidity test, the thermal conductivities of the fabricated sheet were increased due to the rearrangement of PVA and PTFE particles.

Deviation from linear relationship between adhesion strength and surface free energy on a low energy surface

The deviation from the linear relationship between the adhesion strength and surface free energy on a low energy surface was observed for the first time. Although the linear relationship between the adhesion strength and surface free energy in the adhesion between epoxy resin and polymer was previously reported, it was only observed for the region of surface free energy greater than 20 mN/m. In particular, no data were previously reported for the region of surface free energy less than 20 mN/m. The aim of this study was to investigate the existence of the linear relationship in the region of surface free energy less than 20 mN/m. The linear relationship was investigated for the case wherein the epoxy resin adhesive was diluted. No data were previously reported due to the difficulty associated with the preparation of the low surface free energy adherend. In this study, the low surface free energy adherend was prepared by coating the adherend with a low surface energy layer such as a polytetrafluoroethylene particle dispersion composite. The lower limit of the linear relationship between the adhesion strength and surface free energy extended from the conventional value of 20 mN/m to 15.3 mN/m. In the region of surface free energy less than 15.3 mN/m to 2.3 mN/m, the adhesion strength was almost constant, which represents a deviation from the linear relationship. The abovementioned phenomena were observed when the epoxy resin was diluted by egg white by up to 40 vol.%.

Pool boiling performance of TiO2 superhydrophilic and Teflon superhydrophobic surfaces on evenly deposited copper frustums

The miniaturization of electronic devices with ever-increasing functionalities inevitably results in greater thermal load on the devices. Hence, pool boiling, which utilizes the powerful latent heat of vaporization, is introduced as an effective method to manage severe thermal loads on miniaturized electronics. Hydrophobic surfaces tend to augment sufficient nucleation sites via roughening or low surface energy, while hydrophilic surfaces are prone to ample liquid supply, thus facilitating rapid bubble release and preventing surface dry-out. Herein, we compared the heat removal performance of TiO2-coated superhydrophilic and Teflon-coated superhydrophobic surfaces fabricated by aerosol deposition and supersonic spraying, respectively. TiO2 and Teflon particles were deposited on evenly patterned frustums. The resolution of the frustum is categorized as no-frustum, coarse, medium, or fine. We found that the surface wettability had little effect on the critical heat flux (CHF) for the no-frustum and fine cases. However, the CHF and effective heat transfer coefficient (heff) of the superhydrophilic surface increased considerably in the medium case. For the superhydrophobic surface, the presence of frustum deteriorated the pool boiling performance. Frustum texturing enhanced the pool boiling performance by increasing the number of nucleation sites and pathways of fresh liquid supply for the bare and superhydrophilic surfaces, but not for the superhydrophobic surface.

Polyaniline Nanoparticles: A Novel Additive for Augmenting Thermal Conductivity and Tribo-Properties of Mineral Oil and Commercial Engine Oil

The present work demonstrates the novel composition of nanoparticles (NPs) of polyaniline (PANI) solo and, in combination with particles of polytetrafluoroethylene (PTFE) ~230 nm, as a powerful additive (antiwear-AWA and extreme-pressure additive EPA) in lubricating oils. The concentration of PANI NPs varied from 1–4 wt.% in a base oil and commercial 5W30 engine oil. The tribo-performance was evaluated on a four-ball tester. The PANI-based oils significantly enhanced the load-bearing ability, and 3 wt.% of PANI NPs led to enhancement in EP properties by 220% in a base oil and 58% in engine oil. Additionally, hybrid combinations of NPs of PTFE with PANI in base oil were prepared by mixing in a ratio of 3:1 and 2:1 and were explored for possible tribo-synergism in EP properties. The hybrid nano-oils led to the highest reported ~ 535% enhancement in the load-carrying capacity of mineral oil. The lubrication mechanisms for enhanced tribo performance were linked with studies on a scanning electron microscope, an energy-dispersive X-ray analyzer, and with the use of Raman spectroscopy.

Novel Design of Superhydrophobic and Anticorrosive PTFE and PAA + β - CD Composite Coating Deposited by Electrospinning, Spin Coating and Electrospraying Techniques.

A superhydrophobic composite coating consisting of polytetrafluoroethylene (PTFE) and poly(acrylic acid)+ β-cyclodextrin (PAA + β-CD) was prepared on an aluminum alloy AA 6061T6 substrate by a three-step process of electrospinnig, spin coating, and electrospraying. The electrospinning technique is used for the fabrication of a polymeric binder layer synthesized from PAA + β-CD. The superhydrophilic characteristic of the electrospun PAA + β-CD layer makes it suitable for the absorption of an aqueous suspension with PTFE particles in a spin-coating process, obtaining a hydrophobic behavior. Then, the electrospraying of a modified PTFE dispersion forms a layer of distributed PTFE particles, in which a strong bonding of the particles with each other and with the PTFE particles fixed in the PAA + β-CD fiber matrix results in a remarkable improvement of the particles adhesion to the substrate by different heat treatments. The experimental results corroborate the important role of obtaining hierarchical micro/nano multilevel structures for the optimization of superhydrophobic surfaces, leading to water contact angles above 170°, very low contact angle of hysteresis (CAH = 2°) and roll-off angle (< 5°). In addition, a superior corrosion resistance is obtained, generating a barrier to retain the electrolyte infiltration. This study may provide useful insights for a wide range of applications.

High-strength super-hydrophobic double-layered PBO nanofiber-polytetrafluoroethylene nanocomposite paper for high-performance wave-transparent applications

Poly(p-phenylene-2,6-benzobisoxazole) nanofiber (PNF) paper is facing unprecedented challenges in enhancing the interaction between the PNFs and improving its hydrophobicity. In this work, a sol–gel film transformation approach was developed to fabricate high-strength PNF paper. Iron ions formed coordination bonds between PNFs to obtain a preforming three-dimensional, interconnective nanofiber network. Subsequently, polytetrafluoroethylene (PTFE) particles were sprayed onto the surface of the paper, followed by thermal treatment to obtain double-layered PTFE-P/PNF nanocomposite paper. The nanocomposite paper presents incredible tensile strength (271.6 MPa, increased by 52.9%), folding endurance, super-hydrophobicity, and self-cleaning performances. Moreover, it exhibits low dielectric constant (2.06) and dielectric loss tangent (0.0133) values. According to the wave-transparent model for a double-layered dielectric established by Maxwell’s equations, the wave-transparent coefficients of electromagnetic waves incident from both sides of the paper are 97.6% (PNF side) and 96.0% (PTFE/P(S-co-BCB-co-MMA) side), respectively. The PTFE-P/PNF nanocomposite paper possesses great potential in the fields of wave-transparent applications.

Characterization and Tribological Behavior of Electroless-Deposited Ni-P-PTFE Films on NBR Substrates for Dynamic Contact Applications

The use of rubber in dynamic contacts often results in severe degradation and wear of the rubber surface, which is why dynamic rubber seal contacts are usually oil lubricated to ensure their functionality. However, the increasing demand for more convenient and environmentally friendly sealing solutions has prompted the development of dry low-friction rubber coatings. In this work, and for the first time, Ni-P and polytetrafluoroethylene (PTFE) particles were co-deposited by electroless plating on Nitrile Butadiene Rubber (NBR), as a low-cost solution to improve the NBR tribological behavior. A cationic surfactant, cetyltrimethylammonium bromide (CTAB), was added to the plating bath to ensure a homogeneous and efficient incorporation of PTFE into the Ni-P. The optimized PTFE incorporation reached 6.8%, and the composite coating adhesion to NBR was 20% higher than that of nickel-phosphorous (Ni-P) films. The tribological properties of the coatings evaluated by pin-on-disk tests showed a marginal decrease in the coefficient of friction (CoF) (10%, 1 N load), compared to that of Ni-P. However, the tested PTFE-based coatings displayed significantly smoother surfaces with less debris and cracks, clearly demonstrating the benefits of the PTFE in terms of wear resistance for loads up to 5 N.

Smart polydimethylsiloxane sponges with high piezoelectric responses

AbstractIn recent years, soft and stretchable electrets have drawn considerable attention for their wide applications in energy harvesters, sensors, and actuators. However, existing electrets struggle to attain both longevity and stretchability (softness), which means charge retention capability and stretchability (softness) of electrets conflict. In this article, one novel soft and stretchable electret (PPSE) with great electromechanical performance is demonstrated. The PPSE is composed of a polydimethylsiloxane (PDMS) sponge and polytetrafluoroethylene (PTFE) particles. The uniformly distributed pores obtained by the sugar leaching method inside the PPSE can not only accumulate macroscopic dipoles but also provide great stretchability, flexibility, and softness for the material. The resulting PPSE has a large value up to 477 pC/N and great charge stability. Moreover, by the virtue of stretchability and softness, it can output electric signals from twisting, bending, and other mechanical interactions without breaking apart. With these great performances, PPSE will potentially enable applications for actuation, sensing, and energy harvesting.

Enhanced-performance droplet-triboelectric nanogenerators with composite polymer films and electrowetting-assisted charge injection

Droplet-Triboelectric nanogenerators (droplet-TENGs) are a promising renewable energy resource. Enhancing the dielectric surface properties is a primary requirement to increase the output performance of TENG device. In this study, droplet-TENGs are fabricated on indium tin oxide glass substrates with either (1) a pure amorphous fluoropolymer (AF) dielectric film; (2) a composite AF film doped with silk powder (AF/Silk); or (3) a composite AF film doped with polytetrafluoroethylene (PTFE) particles (AF/PTFEp). The energy-harvesting performance of the three devices is examined experimentally with and without the application of electrowetting-assisted charge injection (EWCI). For the AF and AF/Silk devices, the output current increases by approximately 12 times following the application of EWCI. Furthermore, the composite AF/Silk device also improves the current stability. The AF/PTFEp TENG increases the output current by approximately 5 times compared to that produced by the TENG with a pure dielectric layer. Moreover, the performance improvement increases to around 25 times following the application of EWCI. For all three devices, the output current increases with a reducing dielectric layer thickness. The output current also increases with an increasing concentration of the droplet solution. Overall, the results presented in this study provide a useful general understanding of the mechanisms underlying the operation of droplet-triboelectric nanogenerators. This research explores, for the first time, the effect of EWCI on composite material used for droplet-TENG and suggests possible strategies for enhancing the performance of such devices through an appropriate design of the dielectric layer and operating conditions.

Fluorinated epoxy based superhydrophobic coating with robust self-healing and anticorrosive performances

Superhydrophobic surfaces are promising candidates for alleviating notorious corrosion phenomena due to their excellent water repellence. However, superhydrophobic surfaces often possessed with fragile structure stability as well as relatively complex fabrication processes, severely hindering their great potential for broad practical applications in various conditions. Herein, through a facile one-step spray process, a self-healing superhydrophobic coating with excellent anticorrosion performances were developed, by mixing fluorinated epoxy resin (FEP) matrix with polytetrafluoroethylene (PTFE) particles and ceresine wax. The surface maintains robust superhydrophobicity even under harsh conditions (e.g., physical impact, acid, alkali or salt solutions), hence effectively preventing corrosive ions from approaching the surface. Moreover, the superhydrophobic coating also displays remarkable self-healing performances stemming from the introduced ceresine wax, and exhibits excellent recovery of anti-corrosion performance in damaged areas after a rapid heating treatment. The combination of a superhydrophobic performance and self-healing function can significantly enhance the anticorrosion performances of coatings to provide a long-term protection for metals. Therefore, this coating may find promising applications in long-term metal corrosion protection under harsh working conditions.

Probing the state of water in oil-based drilling fluids

Oil-based drilling fluids, also referred to as “invert emulsion drilling fluids”, have been widely accepted as mixtures of water-in-oil (W/O) emulsions and inorganic particles, in which the water droplet–particle interaction has not been considered. Probing the state of water plays an important role in optimizing the performance of oil-based drilling fluids. In this work, hydrophilic BaSO4 and hydrophobic polytetrafluoroethylene (PTFE) particles were added to W/O emulsions. The microstructures of the water droplets and particles in the oil phase were studied using an optical microscope. The state of water was characterized by T2 nuclear magnetic resonance (NMR) and low-temperature differential scanning calorimetry (LT-DSC). Finally, the state of water in actual invert emulsion drilling fluids was verified by two-dimensional T1-T2 NMR. The results showed that the water droplets bound to the hydrophilic BaSO4 particles formed hydrated particle aggregates in the oil phase, while the water droplets and hydrophobic PTFE particles were suspended individually in the oil phase. Thus, the so-called invert emulsion drilling fluids are in fact colloidal suspensions of hydrated particle aggregates in continuous oil phase, rather than W/O emulsions. The findings of this work provide new insights into the formulation and utilization of oil-based drilling fluids.

Effects of defect sizes at different locations on compressive behaviors of 3D braided composites

This paper reports the effects of defect sizes at different locations on the compressive behaviors of 3D braided composites. A polytetrafluoroethylene (PTFE) particle was embedded into the composite to form a defect. Low-velocity impact compression tests, high-speed photographic observations and micro-computed tomography (micro-CT) analyses were performed. Finite element analysis (FEA) models were developed to reveal stress distributions. We found that the compressive strength decreases and damages deteriorate with the defect size. The size effect of the defect in the center region is more significant than that in the surface region. FEA results show that there is a stress concentration around the defect, where the stress magnitude increases with the defect size. The decrease in compressive strength is attributed to stress changes in the shear region caused by defects. We expect such an investigation could be applied to characterize compressive strength in various composites with defects in different sizes and locations.

EXPERIMENTAL AND NUMERICAL INVESTIGATION OF EPOXY HYBRID POLYMER COMPOSITE REINFORCED WITH ZrB2 AND PTFE PARTICLES USING A PIN-ON-DISC TRIBOMETER

Thermal and mechanical performance evaluations of sliding systems are required to avoid the failure of surfaces due to high temperature and a stress focus on a small contact area. This work investigates the thermal and tribological performance of an epoxy composite reinforced with zirconium diboride (ZrB2) and polytetrafluoroethylene (PTFE) particles. Three-dimensional thermal and mechanical finite-element models are used to study the heat generated (heat flux), the temperature field, the stresses, and the deformation of a pin-on-disc system during sliding. These finite-element (FE) results help to study the effect of the coefficient of friction, load, and sliding speed on the contact temperature and stress distribution, which in turn affect the wear. The contact temperature for the epoxy hybrid composite is decreased by 38.9 % due to the addition of fillers. When the load is incremented by 10 N, the contact temperature and stress increase by 25 % and 92 %, respectively. Accurate calculations of the heat generation and stress distribution are considered the key to predicting the sliding system’s performance, the wear characteristics, and the stability of the contacting surfaces.

Particle collision behavior and heat transfer performance in a Na2SO4 circulating fluidized bed evaporator

• Time-domain statistical analysis is used to investigate particle collision behavior. • Polytetrafluoroethylene particles can enhance the heat transfer of Na 2 SO 4 solution. • Effect of operating variables on collision intensity and heat transfer are studied. • Standard deviation and enhancement factor increase with amount of added particles. • Particle collision behavior and heat transfer in Na 2 SO 4 and H 2 O are compared. The particle collision behavior and heat transfer performance are investigated to reveal the heat transfer enhancement and fouling prevention mechanism in a Na 2 SO 4 circulating fluidized bed evaporator. The particle collision signals are analyzed with standard deviation by varying the amount of added particles ε (1%–3%), circulation flow velocity u (0.37–1.78 m·s −1 ), and heat flux q (7.29–12.14 kW·m −2 ). The results show that the enhancement factor reach up to 14.6% by adding polytetrafluoroethylene particles at ε = 3%, u = 1.78 m·s −1 , and q = 7.29 kW·m −2 . Both the standard deviation of the particle collision signal and enhancement factor increase with the increase in the amount of added particles. The standard deviation increases with the increase in circulation flow velocity; however, the enhancement factor initially decreases and then increases. The standard deviation slightly decreases with the increase in heat flux at low circulation flow velocity, but initially increases and then decreases at high circulation flow velocity. The enhancement factor decreases with the increase in heat flux. The enhancement factor in Na 2 SO 4 solution is superior to that in water at high amount of added particles. The empirical correlation for heat transfer is established, and the model results agree well with the experimental data.

Tribocatalysis of homogeneous material with multi-size granular distribution for degradation of organic pollutants

Recently, tribocatalysis driven by mechanical energy has been developed by rubbing two kinds of different materials. In this work, we firstly demonstrated that the friction of the single material also could initiate the tribocatalysis for degrading organic dyes. Under magnetic stirring, the multi-size granular polytetrafluoroethylene (PTFE) particles were triboelectrically charged, among which the collision between large and small particles would cause high energy electrons on large particles to transfer to small ones. These triboelectric charges on PTFE particles could react with adsorbed oxygen molecules or water to generate reactive oxygen species, and then promoted the degradation process of organic dyes together with oxidant holes. We further investigated the experimental parameters, such as stirring speed, size and quantity of stirring bar, to optimize the tribocatalytic performance. What’s more, the PTFE tribocatalysis possessed high durability for multiple recycling runs with > 90% degradation efficiency of Rhodamine B, as well as well universality for eliminating other pollutants. Finally, we proposed a plausible tribocatalytic mechanism of multi-size granular PTFE according to the detected reactive oxygen species and the determined intermediates. This study provides new insights into tribocatalysis, and demonstrates that the single material with different particle sizes can also be used as catalyst to drive tribocatalytic process.