FEP Films Research Articles

Chemical Activation Boosted Interface Interaction between Poly(tetrafluoroethylene-co-hexafluoropropylene) Film and Silver Coating.

To enhance the interfacial adhesion between poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP) film and functional coatings, such as silver (Ag) coating, among others, the surface activation of FEP film has to be performed. Among various activation strategies, chemical activation, such as using naphthalene sodium system, is one of the most efficient methods. However, the effect of chemical activation on the interface interaction between the activated FEP and functional coating is rarely investigated. Herein, the FEP film was activated by naphthalene sodium solution under different conditions, and then the Ag layer was coated onto its surface by vacuum Ag deposition. Based on experimental results and density function theory (DFT) calculation, it is indicated that oxygen-containing functional groups (such as C=O and C-OH groups), introduced onto the surface of FEP by the chemical activation, play a key role in boosting the interface interaction, which is due to the strong interaction between the oxygen-containing functional groups and Ag atoms. In addition, the concentration of naphthalene sodium solution, activation time, and winding speed of Ag- deposition can have a significant impact on the microstructures of Ag coating and the interfacial adhesion between the activated FEP and Ag coating. Under the conditions of high concentration (0.9 M), medium activation time (15 min), and high winding speed (0.8 m min-1), there is the best interface adhesion.

An air-triggered contact-separation rotating triboelectric nanogenerator based on rotation-vibration-pressure conversion

Energy harvesting using triboelectric nanogenerators (TENGs) has demonstrated great potential in powering sensor network nodes and become a promising alternative for battery-free portable and wireless electronics. Unlike most existing rotational sliding-mode TENGs, an air-triggered contact-separation rotating triboelectric nanogenerator (AT-TENG) based on rotation-vibration-pressure conversion is proposed to reduce the violent collision of triboelectric materials and enhance the durability in this paper. The distinguishing feature of the AT-TENG was indirectly-excited contact separation mode along with the air-film interaction, where the rotational motion was converted into an elastic sheet vibration via the magnetic coupling and then the periodic contact or separation between the FEP film and aluminum plate was induced by the alternating air pressure. The feasibility of the presented AT-TENG was verified by theoretical analysis, fabrication and experiments. The results indicated that the distance of PVC to aluminum, radius ratio of the FEP to PVC, chamber volume (denoted by the acrylic ring height), magnet coefficient and rotational speed brought a significant effect on the output behaviors of the AT-TENG. There was an optimal PVC-aluminum distance of 0.1 mm as well as the maximum output voltage increased firstly and then decreased with the enhancement of radius ratio. Also, the output voltage was roughly enhanced with the increasing ring height except a maximum value occurred at h = 3.6 mm and demonstrated a reducing trend as the magnet coefficients was increased. In addition, the AT-TENG could achieve a maximum voltage of 367 V, maximum average power of 128.7 μW, and highest charging electricity of 14.45 mJ in the experiments. Besides, a parallel 200 LEDs could be efficiently powered by the AT-TENG. Furthermore, the AT-TENG demonstrated a long-term durability and stability through the 106444-excitation testing. It is expected that this work can offer a useful reference for further improvements of the rotational TENGs.

Ozonolysis of Terpene Flavor Additives in Vaping Emissions: Elevated Production of Reactive Oxygen Species and Oxidative Stress.

The production of e-cigarette aerosols through vaping processes is known to cause the formation of various free radicals and reactive oxygen species (ROS). Despite the well-known oxidative potential and cytotoxicity of fresh vaping emissions, the effects of chemical aging on exhaled vaping aerosols by indoor atmospheric oxidants are yet to be elucidated. Terpenes are commonly found in e-liquids as flavor additives. In the presence of indoor ozone (O3), e-cigarette aerosols that contain terpene flavorings can undergo chemical transformations, further producing ROS and reactive carbonyl species. Here, we simulated the aging process of the e-cigarette emissions in a 2 m3 FEP film chamber with 100 ppbv of O3 exposure for an hour. The aged vaping aerosols, along with fresh aerosols, were collected to detect the presence of ROS. The aged particles exhibited 2- to 11-fold greater oxidative potential, and further analysis showed that these particles formed a greater number of radicals in aqueous conditions. The aging process induced the formation of various alkyl hydroperoxides (ROOH), and through iodometric quantification, we saw that our aged vaping particles contained significantly greater amounts of these hydroperoxides than their fresh counterparts. Bronchial epithelial cells exposed to aged vaping aerosols exhibited an upregulation of the oxidative stress genes, HMOX-1 and GSTP1, indicating the potential for inhalation toxicity. This work highlights the indirect danger of vaping in environments with high ground-level O3, which can chemically transform e-cigarette aerosols into new particles that can induce greater oxidative damage than fresh e-cigarette aerosols. Given that the toxicological characteristics of e-cigarettes are mainly associated with the inhalation of fresh aerosols in current studies, our work may provide a perspective that characterizes vaping exposure under secondhand or thirdhand conditions as a significant health risk.

Self-Aligned InGaZnO Thin-Film Transistors and Circuits on Transparent Thin Glass and FEP Film

Self-Aligned InGaZnO Thin-Film Transistors and Circuits on Transparent Thin Glass and FEP Film

Changes in optical properties of polymeric materials due to atomic oxygen in very low Earth orbit

Atomic oxygen (AO) is the dominant constituent of the residual atmosphere in low Earth orbit (LEO). AO collides with spacecraft at a velocity of 8 km/s, causing oxidation and erosion of polymeric materials. Particularly in very low Earth orbit (VLEO) at altitudes below 300 km, the AO density is at least ten times that at 500–700 km, and the concentration of molecular nitrogen (N2) is 10% or more. Such high-flux AO and N2 can cause nonlinear processes and mass losses for polymers. This study aims to clarify the optical property changes for polymeric materials exposed to LEO and VLEO in the Material Degradation Monitor (MDM) mission onboard the Super-Low-Altitude Test Satellite (SLATS). The AO and N2 fluences and the UV irradiances were estimated using the NRLMSISE-00 atmospheric and solar radiation models. The relationships were investigated between the changes in CCD images and the estimated fluences of the samples. For silsesquioxane (SQ)-coated polyimide film, the diffuse reflection of visible light increased noticeably with an AO fluence above 1 × 1021 atoms/cm2. The formation of a silica layer on the coating induces cracks. For silver-coated FEP films, the diffuse reflection increased entirely at AO fluences above 3 × 1021 atoms/cm2. The AO and N2 collisions would erode and roughen the FEP surfaces. Visible transmission through silver-coated FEP films also increased locally with increasing AO fluence, indicating that some AO oxidized the silver layer despite the presence of an Inconel (Ni alloy) layer. The visible reflection from Beta Cloth was decreased by its reaction with UV. Further, the competitive reactions with UV and AO resulted in two-step changes in the visible reflection from the ETFE polymer (cable covering).

Effect of Chemical Activation on Surface Properties of Poly(tetrafluoroethylene-co-hexafluoropropylene) Film.

Due to their low surface energy, poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP) films must be treated by chemical or physical activation methods before using. Among these activation strategies, using sodium naphthalene solution is a popular one. However, the effect of this strategy's chemical activation conditions on the surface properties of the FEP film is rarely discussed. In this study, FEP films were chemically activated by the sodium naphthalene solution with adjusting concentration, solvent, and activation time. With increasing concentration and activation time, many granular substances appeared on the surface of the FEP film. When tetrahydrofuran was used as a solvent, the color of the film gradually turned brown; when 1,3-dimethyl-2-imidazolidinone was chosen as the solvent, the color change was not very significant. The contact angle was significantly reduced from 112° before activation to 26° after activation, and the surface energy was greatly enhanced from 34 mN m-1 before activation to 66 mN m-1 after activation. In addition, compared with the FEP samples treated by Ar plasma, the sodium naphthalene system showed a stronger activation ability. Activated FEP films that suffered from the Ar plasma treatment could still maintain a higher energy surface than that of the pristine FEP.

Multi-Tube Helmholtz Resonator Based Triboelectric Nanogenerator for Broadband Acoustic Energy Harvesting

Acoustic energy, especially broadband low-frequency sound energy is part of the environmental mechanical energy acquisition cannot be ignored. Herein, a multi-tube parallel Helmholtz resonator-based triboelectric nanogenerator (MH-TENG) is investigated to reap sound energy in low-frequency noise environments. The designed MH-TENG consists of a modified Helmholtz resonator and a thin-film TENG transducer. The core materials of the TENG transducer are aluminum, FEP film, and carbon. To further clarify the influence of the modified Helmholtz resonator on the conversion performance of MH-TENG, the acoustic characteristics of the improved resonators are systematically studied. A series of experiments show that the multi-tube parallel Helmholtz resonator structure has a better sound wave collection effect. Meanwhile, the flexible film TENG can reduce the optimal output frequency of the device. The power generation performance and the bandwidth of the MH-TENG are significantly improved by adopting a multi-tube Helmholtz resonator. Within the frequency bandwidth range of 230 Hz, MH-TENG can effectively improve the efficiency of acoustic energy harvesting. 110 LEDs and an electronic thermometer can be powered by the sound-driven MH-TENG. In addition, the MH-TENG has a good capacitor charging performance, which is conducive to its application in ambient sound energy harvesting.

Tilting separation simulation and theory verification of mask projection stereolithography process

Purpose This study aims to accurately simulate the tilting separation process of mask projection stereolithography (MPSL) and verify the tilting theory. Design/methodology/approach The finite element separation models of MPSL 3D printing process were established. The established models simulated both tilting and pulling-up separation process by changing the constraints and boundary conditions. The bilinear cohesive curves were used to define the separation interface. The stress distribution of the cured part and FEP film at different times during the whole separation process was extracted. Different orientations of pulling-up and tilting were also compared for stress distribution. The stress change was analyzed for the center and edge points of the upper surface of cured part. Findings The results showed that the stress increased with the separation speed, and the stress at the edge position of exposure area was greater than the internal position. The tilting traction stress distribution was affected by the exposure area function and the velocity distribution. Alternation of the exposure area function changed the cohesive stiffness. The non-coincidence of the calculated traction stress with the input bilinear cohesive curve reflected the influence of the material properties and the separation methods. The high-speed side of tilting had fast separation and high traction stress. Originality/value This study proposes a technical method for simulation tilting separation and verified the tilting theory. The cohesive zone model was proved applicable to the tilting traction stress calculation.

Space Charge Distribution Measurement in FEP Film Irradiated by Proton

Space Charge Distribution Measurement in FEP Film Irradiated by Proton

Electrodeposition of iron phosphide film for hydrogen evolution reaction

The hydrogen evolution reaction (HER) by electrochemical water splitting is part of a sustainable and scalable process to produce H2. Hence, the design of a highly efficient and low-cost electrocatalyst is in demand. We report the development of a straightforward and cost-effective method to electrodeposit an iron phosphide (FeP) film on a copper electrode at room temperature. The as-deposited FeP film was able to support current density of −10 mA/cm2 at overpotentials of 66 mV in 0.5 M sulfuric acid (H2SO4, pH=0.3), 131 mV in 1.0 M phosphate buffer (PB, pH=6.4) and 110 mV in 1.0 M potassium hydroxide (KOH, pH=14.0) solution, as well as a Tafel slope of 55 mV/dec, 108 mV/dec, 60 mV/dec, respectively. The film has excellent stability during HER catalysis under acidic and neutral conditions, as shown by electron microscopy and X-ray photoelectron spectroscopy.

Design and analysis of a vibration energy harvester using push-pull electrostatic conversion

Methods of electrostatic conversion are available for harvesting energy where there are ambient vibrations. However, most of the previous work in the literature has addressed applications with high frequencies. In this study, we are not only implementing an electret-based energy harvester for low-frequency applications but also evaluating the effect of parameters, including vibration rates, accelerations, electret surface potential, e.g. on the efficiency of electrostatic energy harvesting (EH). A prototype system, with the size of 4 × 28 cm3, was built and constructed to accomplish experimental analysis, and the corona triode process was used to prepare electrets by charging Teflon FEP films. In the electret surface potential range of 300–1800 V, vibration frequency range of 2–45 Hz, and acceleration range of 0.1–1.0 g, the effect of parameters on the EH efficiency was experimentally tested. To predict and maximize the performance of the system, a mathematical response surface model (RSM), validated experimentally < 9.5% error. The maximum peak-peak voltage output of 318 V was predicted using this model for the electret surface potential of −1800 V, and vibration frequency of 16 Hz. Moreover, harvested energy was ∼ 900 μJ (∼0.8 µJ per mechanical cycle) in a minute though low frequencies (<20 Hz), which can be easily enhanced to more than 1 mJ with system optimization. We suggest our device can be used in numerous low-frequency applications, and our predictive model can also be used to optimize the efficiency of other electrostatic energy harvesters based on electrets.

Self‐assembly Mesoporous FeP Film with High Porosity for Efficient Hydrogen Evolution Reaction

AbstractExploring efficient noble metal‐free electrocatalysts is of significance for water electrolysis. In this work, we fabricated a high‐efficiency self‐supporting electrode with mesoporous FeP film coated on carbon cloth (meso‐FeP film/CC) for the hydrogen evolution reaction (HER). Compared with nanoparticle‐stacked disordered porous structure, the ordered mesoporous iron phosphide film exhibits high porosity as high as 2.3×1017 site per mg, as well as small pore size and uniform pore distribution, which enables the exposure of abundant active sites. Moreover, the self‐supporting structure with enhanced conductivity further optimizes its electrocatalytic performance towards the HER. As a result, the meso‐FeP film/CC displays a low overpotential (65 mV at current density of 10 mA cm−2) and a small Tafel slope (44 mV dec−1) in acid condition, which is competitive among most of noble‐metal free electrocatalysts.

Mixing characteristics of a film-exciting flapping jet

We have recently discovered a new type of self-excited flapping jets due to a flexible film whose leading edge is fixed at the nozzle exit [Exp Ther Fluid Sci, 106, 226-233]. This paper is to report the experimental investigation on mixing characteristics of the jet induced by a rectangular FEP film. Hot wire anemometry and flow visualization are used to examine the flapping jet flow versus the non-flapping counterpart. Experiments are conducted under the following conditions: i.e., L/D = 1.0 (fixed), W/D = 0.03 ~ 1.0 (varying) and Re = 10000 ~ 45000 (varying); where W and L are the film's width and length, D is the nozzle-exit diameter, and Re is the Reynolds number defined by ReUoD/ν with Uo and ν being the jet-exit velocity and fluid viscosity.It is found that the jet-flapping frequency fF varies with W in a complex fashion while it grows roughly linearly with increasing Uo for W/D ≥ 0.5. The flapping Strouhal number StFfFD/Uo ranges in 0.13 ≤ StF ≤ 0.23 for Re = 15,000 ~ 45,000. These Strouhal numbers are substantially lower than that (≈ 0.45 ~ 0.7) for the primary vortex generation in the free jet, but one to two orders of magnitude higher than those from the conventional self-exciting fluidic devices. In general, the flapping jet decays and spreads more rapidly than does the free jet. As W increases, the decaying and spreading rates both grow. Of significance, the centerline evolutions of Taylor and Kolmogorov scales versus the integral scale are examined to characterize the small scales of turbulence against the large-scale motion.

Highly solderability of FeP film in contact with SnAgCu solder

New under bump metallization (UBM) is required for future microelectronics to minimize reliability concerns with solder interconnects. In this study, electroless FeP film was prepared as UBM. Solderability of electroless NiP, electrodeposite Fe and electroless FeP films with eutectic SnAgCu solder was investigated by static wetting tests and wetting balance measurements. Results revealed that the solderability of NiP film has almost no change with thermal aged for the film in air atmosphere increasing. The contact angles for FeP and Fe films with SnAgCu solder increased and the maximum wetting force decreased with heating time increasing from 0 h, 48 h, 89 h–160 h at 180 °C. But the solderability of FeP film was found to be better than those of NiP and Fe whether the films in base or thermal aged at 180 °C for 89 h. Even after thermal aged in air atmosphere at 180 °C for 160 h, the FeP also performed the smallest contace angle compared with the NiP and the Fe. Oxide layer on the surface of FeP was much easier to be removed by rosin mildly activated flux during reflow process because loose structure. It was proved to be the key for the highly solderability of electroless FeP.

Functional macroporous iron-phosphorous films by electrodeposition on colloidal crystal templates

Pseudo-ordered macroporous iron-phosphorous (Fe-P) films have been electrodeposited potentiostatically from a citrate-sulfate bath onto Au surfaces pre-patterned with a colloidal crystal mask of polystyrene spheres of 350 nm in diameter. The electrolyte contained sodium hypophosphite as the P source, enabling the incorporation of 6–14 at.% P. For comparative purposes, continuous films have been obtained galvanostatically on unpatterned Au surfaces. In both cases, the P content could be varied to a certain extent by adjusting the deposition potential or current density. Tunable microstructure and magnetic response was observed due to the dissimilar chemical composition, with coercivity values being larger in the macroporous films. Additionally, wettability analyses showed that these were more hydrophobic, reaching contact angle values of about 130∘. In spite of their hydrophobic character, the samples were catalytic toward oxygen evolution reaction (OER) in alkaline media. The macroporous Fe-P films showed faster kinetics for OER than their nonporous counterparts. Our results show that electrodeposited porous Fe-P based materials show an interesting combination of properties which make them appealing for applications including water cleaning, soft-magnetic components, or electrocatalytic production of oxygen, to name a few.

Electrodeposited Iron Phosphide Film As an Efficient Electrocatalyst for Hydrogen Evolution Reaction

To scale up hydrogen evolution reaction from electrochemical water splitting, a remaining challenge is to replace precious Pt catalysts with cost-effective catalysts. Recently, iron phosphide (FeP) was discovered to be a good substitute for platinum because of the extreme abundance and low cost of iron. Unfortunately, the synthesis of FeP typically requires harsh conditions, which usually cause the decomposition of phosphide precursors and the generation of highly corrosive and flammable phosphorus. Herein, we developed a straightforward and cost-effective method to electrodeposit FeP film on copper electrode at room temperature. The prepared FeP film only requires an overpotential of 66 mV in 0.5 M H2SO4, 131 mV in 1.0 M PBS and 110 mV in 1.0 M KOH, to achieve the current density of 10 mA/cm2, as well as Tafel slope of 55 mV/dec, 108 mV/dec, 60 mV/dec, respectively. In addition, the FeP shows excellent stability over 24 hours and gives about 100% Faradaic efficiency.

A new type of self-excited flapping jets due to a flexible film at the nozzle exit

This paper reports a new type of flapping turbulent jets that are self-excited by flutter of a flexible film with a leading edge fixed axially and centrally at a round nozzle exit. Both flutter conditions of a film and flapping-jet characteristics are investigated by varying the film material and dimensions of length (L), span (S) and thickness (δ). Visual observation, flow visualization and hot-wire anemometry are used to examine the flapping jet versus the free counterpart without involving any film. Experiments are made at L/D = 0.5 ∼ 2.0 and the jet Reynolds number of Re = 10,000 to 50,000; where Re ≡ UoD/ν with D, Uo and ν being the jet-exit diameter, exit-averaging velocity and fluid viscosity, respectively.Results show that the film’s flutter domain reduces with increasing its overall stiffness and varies with the film’s shape, size and thickness. The jet-flapping frequency fF rises as either L decreases or Uo increases. For the rectangular FEP film of L/D = 0.5 ∼ 2.0, the jet-flapping Strouhal number StF ≡ fFD/Uo varies over the range of 0.05 ≤ StF ≤ 0.23. This StF is noticeably lower than that (≈ 0.5 ∼ 0.7) of the primary vortex passage in the non-flapping free jet, but extraordinarily one to two orders of magnitude higher than those for the self-excited oscillation of a jet from conventional fluidic nozzles.

Angle-shaped triboelectric nanogenerator for harvesting environmental wind energy

Recently, flutter-driven triboelectric nanogenerator (TENG) has shown huge potential in wind energy harvesting from ambient environments. However, almost all the reported devices are based on parallel structure which suffers from a critical problem of insufficient contact between triboelectric surfaces. In this work, we propose an angle-shaped TENG (AS-TENG) with the above issue resolved. The device is based on two Al layers stacked to form an angle shape and a FEP film positioned in between by sharing a common side. Thanks to this design, the FEP film can contact fully and intimately with the Al layers to facilitate the effect of contact electrification and electrostatic induction. Compared with the existing parallel-structured TENG, the AS-TENG shows an overwhelming output performance because of the enhanced contact area. Furthermore, the AS-TENG is introduced a wedge-shaped wind guide channel which can provide a driving force for the flutter and hence lower the start-up wind speed largely. To further enhance the electric output, the AS-TENGs can be facilely integrated into a 360° radial array, showing an enlarged windward area and a high level of integration. The AS-TENG array can be applied to harvest outdoor weak wind and act as a direct power source to charge a capacitor or drive electronic devices. This work provides a design strategy for natural weak wind scavenging which may push forward the practical applications of TENG for wind power.

Bio-inspired design of hierarchical FeP nanostructure arrays for the hydrogen evolution reaction

Hierarchical FeP nanoarray films composed of FeP nanopetals were successfully synthesized via a bio-inspired hydrothermal route followed by phosphorization. Glycerol, as a crystal growth modifier, plays a significant role in controlling the morphology and structure of the FeO(OH) precursor during the biomineralization process, while the following transfer and pseudomorphic transformation of the FeO(OH) film successfully give rise to the FeP array film. The as-prepared FeP film electrodes exhibit excellent hydrogen evolution reaction (HER) performance over a wide pH range. Theoretical calculations reveal that the mixed P/Fe termination in the FeP film is responsible for the high catalytic activity of the nanostructured electrodes. This new insight will promote further explorations of efficient metal phosphoride-based catalysts for the HER. More importantly, this study bridges the gap between biological and inorganic self-assembling nanosystems and may open up a new avenue for the preparation of functional nanostructures with application in energy devices.

Mechanisms and Characterization of the Pulsed Electron-Induced Grafting of Styrene onto Poly(tetrafluoroethylene-co-hexafluoropropylene) to Prepare a Polymer Electrolyte Membrane.

During the pulsed-electron beam direct grafting of neat styrene onto poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP) substrate, the radiolytically-produced styryl and carbon-centered FEP radicals undergo various desired and undesired competing reactions. In this study, a high-dose rate is used to impede the undesired free radical homopolymerization of styrene and ensure uniform covalent grafting through 125-μm FEP films. This outweighs the enhancement of the undesired crosslinking reactions of carbon-centered FEP radicals and the dimerization of the styryl radicals. The degree of uniform grafting through 125-μm FEP films increases from ≈8%, immediately after pulsed electron irradiation to 33% with the subsequent thermal treatment exceeding the glass transition temperature of FEP of 39°C. On the contrary, steady-state radiolysis using 60Co gamma radiolysis, shows that the undesired homopolymerization of the styrene has become the predominant reaction with a negligible degree of grafting. Time-resolved fast kinetic measurements on pulsed neat styrene show that the styryl radicals undergo fast decays via propagation homopolymerization and termination reactions at an observed reaction rate constant of 5 × 108 l · mol-1 · s-1. The proton conductivity of 25-μm film at 80°C is 0.29 ± 0.01 s cm-1 and 0.007 s cm-1 at relative humidity of 92% and 28%, respectively. The aims of this work are: 1. electrolyte membranes are prepared via grafting initiated by a pulsed electron beam; 2. postirradiation heat-treated membranes are uniformly grafted, ideal for industry; 3. High dose rate is the primary parameter to promote the desired reactions; 4. measurement of kinetics of undesired radiation-induced styrene homopolymerization; and 5. The conductivity of prepared membranes is on par or higher than industry standards.