PTFE Film Research Articles

Study on Plasma Surface Modification of Hydrophobic Materials

The hydrophobic materials were treated by plasma continual treater to achieve its surface modification and improve its wettability. The influences of treating time, discharge power, working gases and gas pressure on the surface modification of the materials have been investigated. The chemical states and species on the surface of materials have been investigated by some technologies such as contact angles. After plasma surface treatment, the contact angles of PTFE sharply decrease, and the alkali liquid absorption of PE increased to three times of its weight. The contact angles of silicon rubber and polyester decreased remarkably after surface modification. PTFE films were grafted with crylic acid to evaluate the ageing. The effect of vacuum ultraviolet radiation to surface modification was initially described. The results of experiment demonstrate that the better wettability of hydrophobic material can be achieved. The technique and the equipment have the promotional value for industrial application.

An MXene/cellulose nanofiber-based multi-parametric tactile sensor for object material identification

Abstract We propose a novel multi-parametric tactile sensor that can realize force and slip sensing during the contact between a manipulator and a target. The pressure-sensitive unit of this sensor is prepared by homemade MXene and cellulose nanofiber (CNF) composite conductive film, which has high sensitivity of pressure-sensitive response. The triboelectric unit is made of a chemically stable PTFE film with high electron-acquiring ability as the triboelectric sensing layer together with metal electrodes. Experiments have demonstrated that the prepared sensors have high sensitivity, fast response, and excellent durability and stability over 5000 cycles. Combined with the established machine learning algorithm model, the pressure and triboelectric signals of this multi-parametric tactile sensor were used to recognize 15 types of materials with similar characteristics and with 94.33% identification accuracy. This work shows the great potential of multi-parametric tactile sensors for applications in item sorting, human-machine interaction, and other fields.

Periodic atmospheric plasma substrate treatment to improve the hydrophobicity of sputtering PTFE films

Periodic atmospheric plasma substrate treatment to improve the hydrophobicity of sputtering PTFE films

Scanning ex situ solid-state magnetic resonance imaging on polymeric films using a static magnetic field gradient by an electromagnet.

A new technique for ex situ solid-state nuclear magnetic resonance imaging of polymeric films has been developed. This method uses the static magnetic field gradient generated by a water-cooled copper electromagnet. The imaging process involves scanning the sample in the plane of the film under a static magnetic field gradient. Two-dimensional (2D) 19F MRI measurements are attempted, where the fast Fourier transform (FFT) spectra of the second half of a Hahn echo peak is used for the depth (X-axis) direction, and the sample film is mechanically moved for the Y-axis, which is in-plane with respect to the film surface and normal to the inter-magnetic-pole line (Z-axis). The sample is a poly(tetrafluoroethylene) [PTFE] film with carved stripes on its surface. Furthermore, three-dimensional (3D) measurements of the film surface and thickness orientations were also performed for an analogous PTFE film. For 2D profiling on the film surface, 2D sample-moving was used. For depth profiling, FFT spectrum analysis was undertaken for each voxel situated at a specific (Y, Z) coordinate within the film. As a result, a 3D image of the sample and its corresponding geometry were obtained, although the scanning area was restricted to a part of the sample. Finally, numerical simulations of the spatial distribution of the static magnetic field were performed to confirm the validity of the present method.

Formaldehyde degradation by soft-sliding-electrification-induced air ionization

Formaldehyde (HCHO), a highly toxic and carcinogenic gas, is the most common indoor air pollutant and a threat to human health. Developing simple and effective technological routes to achieve sustainable degradation of HCHO has become a common goal. In this work, we reported a self-powered air-ionized HCHO degradation system based on a soft-sliding freestanding mode triboelectric nanogenerator (SSF-TENG). The sliding-electrification process between soft rabbit fur and a robust PTFE film enables the generation of electrical outputs of up to ten thousand volts that can trigger air breakdown. The generated O3, ·OH and other highly oxidizing substances could degrade HCHO into CO2 and H2O. Through a standard ball gap platform based on two hollow Cu balls, the voltage of air discharge was measured to be between 11.2 kV and 14.4 kV. For demonstration, the SSF-TENG was applied to two parallel disk-shaped Cu electrodes to continuously breakdown the air with a peak discharge current of 6 mA. The system can produce a maximum O3 concentration of 1.2 ppm within 50 minutes. Moreover, the HCHO concentration can be reduced from 1.6 ppm to 0 within 20 minutes, and the degradation speed reaches 0.08 ppm/min. This work highlights the application of triboelectric microplasma in pollutant removal, which has great potential in self-powered environmental purification.

Terajet-assisted time-domain super-resolution imaging

Large-scale applications of real-time terahertz (THz) imaging are often limited by the spatial resolution of a THz microscope. One of the simplest approaches to circumvent this problem in practice and achieve resolution below the diffraction limit consists in placing a dielectric particle with a size comparable to the radiation wavelength in the vicinity of the focal plane of the THz imaging system. Here, we theoretically consider the transmittance of a THz Gaussian beam through a Teflon sphere to further analyze experimental results on THz superresolution imaging. We address the resolution beyond the diffraction limit (the experimentally determined value is 0.38λ at 0.46 THz) through the superlens effect of the terajet generated by the mesoscale sphere owing to propagating and evanescent partial waves in the terajet. Due to the coupling of the dielectric sphere and time-domain THz spectrometer, we can detect a 10 µm thick PTFE film, which is almost transparent (98% transmittance) in the THz frequency range. The correlation between the transmittance spectrum of the dielectric sphere and the quality of THz images of thin, nonconducting films collected at different frequencies has been demonstrated experimentally and considered analytically. Our study is relevant for hyperspectral imaging applications and further development of the sphere-coupled time-domain THz imaging technique.

Additional kinetic energy harvesting with extra electrodes by single electrode droplet-based electricity generator (SE-DEG)

The utilization of water energy through the Single Electrode Droplet-Based Electricity Generator (SE-DEG) represents a universal and high-efficiency method for water energy harvesting. Previous research has extensively elucidated the working principle of SE-DEG based on bulk effect. However, scant attention has been paid to the investigation of the electrical characteristics surrounding the SE-DEG. Remarkably, the electrical characteristics around the SE-DEG can be exploited to generate electricity and harvest corresponding energy. Here we evaluate the electrical characteristics around the SE-DEG by arranging extra electrodes. An interesting phenomenon is found that, on the premise of no contact between extra electrodes and the droplet, there is opposite electricity output from extra electrodes synchronously when the droplet contacts on the PTFE film and SE-DEG electrode and outputs the electricity. This phenomenon is comprehensively explained and verified from working mechanism, the impacts of different arrangements and the array design of extra electrodes. Significantly, utilizing the electrical characteristics could harvest additional kinetic energy with extra electrodes in SE-DEG. This investigation is expected to provide new insights into the future harnessing of water kinetic energy within the SE-DEG framework.

An electrochemical H2S sensor based on the screen printing Fe@Pt/C/PTFE sensing electrode.

A novel electrochemical gas sensor for sensitive detection of H2S at room temperature is constructed based on the Fe@Pt/C composite material. The core-shell structured Fe@Pt catalyst was synthesized by a two-step reduction method and physically dispersed in Vulcan XC-72 carbon powders. The core-shell structure increases the effective catalytic surface area of Pt while significantly reducing the usage of the noble metal Pt, leading to improved catalytic performance and decreased production costs. Additionally, the mature screen-printing process is used to coat the catalyst film. A waterproof and breathable PTFE film was used as the substrate and the parameters in the screen printing process were also optimized to achieve the best gas sensing performance of the electrode film. Through the detection of hydrogen sulfide (H2S) with different concentrations, it is found that the sensor strictly shows linear correlation in the range of 1-20 ppm, R2 = 0.99974. Notably, the sensor exhibits high sensitivity (658.45 nA ppm-1) and a low detection limit of 0.33 ppm. Moreover, the consistency and stability of the sensor are satisfactory. The constructed gas sensor is expected to be well applied to industrial H2S detection.

Electret Modulation Strategy to Enhance the Photosensitivity Performance of Two-Dimensional Molybdenum Sulfide.

Due to the limited light absorption efficiency of atomic thickness layers and the existence of quenching effects, photodetectors solely made of transition metal dichalcogenides (TMDs) have exhibited an unsatisfactory detection performance. In this article, electret/TMD hybridized devices were proposed by vertically coupling a MoS2 channel and the PTFE film, which reveals an optimized photodetection behavior. Negative charges were generated in the PTFE layer through the corona charging method, akin to applying a negative bias on the MoS2 channel in lieu of a traditional voltage-driven back gate. Under a charging voltage of -6 kV, PTFE/MoS2 devices reveal improved photodetection performance (Rhybrid = 67.95A/W versus Ronly = 3.37 A/W, at 470 nm, 1.20 mW cm-2) and faster recovery speed (τd(hybrid) = 2000 ms versus τd(only) = 2900 ms) compared to those bare MoS2 counterparts. The optimal detection performance (2 orders of magnitude) was obtained when the charging voltage was -2 kV, limited by the minimum of the carrier density in MoS2 channels. This study provides an alternative strategy to optimize optoelectronic devices based on the 2D components through non-voltage-driven gating.

Automated Quantification of Interlaminar Delaminations in Carbon-Fiber-Reinforced Polymers via High-Resolution Ultrasonic Testing.

This article presents a method of ultrasonic testing (UT) that detects and quantifies interlaminar delaminations in CFRP composites with high resolution in terms of both spatial resolution in the planar dimension and depth into the laminate. Unidirectional and woven CFRP laminates were fabricated for this study, with a PTFE film inserted at various depths throughout the laminate to act as intentional crack initiation sites. All samples were mechanically tested via a three-point, end-notched flexure (ENF) test, followed by a quantification of the extent of the induced interlaminar delaminations using UT and X-ray computed tomography (CT). UT analysis for unidirectional CFRP samples was able to show a clear contrast between the delaminated area and the non-delaminated area. UT analysis of the woven CFRP samples yielded comparable results but required finer tuning of analysis parameters due to the interlocking woven fabric. CT results revealed a significant contrast between the crack and composite; thus, fine geometrical features of the crack front could be observed. UT and CT measurements were then compared, revealing an average difference of 1.09% in the delamination area, with UT overestimating as compared to CT. A UT depth study was also performed to automatically locate the interlaminar delamination at different depths throughout the components, with the delamination being predicted within one lamina interface for all samples. These results demonstrate UT's ability to accurately detect and quantify the extent and location of interlaminar delaminations due to bending.

Characterization of corona discharge treatment on PTFE surface for TENG applications

As for practical application of triboelectric nanogenerators (TENGs), corona discharge treatment (CDT) is often utilized further to enhance its power outputs by injecting charges. We report compositional analysis and corresponding triboelectric outputs of Poly(1,1,2,2-tetrafluoroethylene) (PTFE) based TENGs. PTFE and Al based TENGs with various PTFE film thickness are fabricated and their performances are measured with different CDT applied bias. XPS depth profile analysis reveals the relation of triboelectric outputs and depth of oxygen ions. Our discovery may give insight in the future development of high performance TENGs using CDT.

Surface Activity, Wetting, and Aggregation of a Perfluoropolyether Quaternary Ammonium Salt Surfactant with a Hydroxyethyl Group.

This paper reports the synthesis of a novel quaternary surfactant containing a hydroxyethyl group (PFPE-C) and the surface properties of its aqueous solution (investigated by comparisons with two structurally similar chemicals, dodecyl-(2-hydroxyethyl)-dimethylammonium chloride (DHDAC) and PFPE-A). The minimum surface tension (γCMC) and critical micelle concentration (CMC) of the PFPE-C aqueous solution were 17.35 mN/m and 0.024 mmol/L, respectively. This study confirms that surfactants containing hydroxyethyl groups efficiently reduce the surface tension of aqueous solutions, and fluorocarbon surfactants exhibit better surface activity than ordinary hydrocarbon surfactants with similar structures. The micellization, aggregation, air-water interfacial adsorption, and wettability of PFPE-C aqueous solutions have been systematically investigated. Highly concentrated PFPE-C aqueous solutions exhibit good wettability on PTFE and paraffin films. Moreover, the aggregates of PFPE-C in the aqueous solution were clearly seen as vesicles on Cryo-TEM micrographs. Primary biodegradation results indicate that 19% of PFPC-C can be degraded within one week.

Friction Characteristics of SUS440C/Si3N4 Lubricated by Polytetrafluoroethylene Under Cryogenic Environment

Abstract The friction characteristics of SUS440C-Si3N4 lubricated by polytetrafluoroethylene (PTFE) under cryogenic environment have not been researched well. The lubrication mechanisms in such friction condition need to be clarified to improve the fidelity of performance modeling for ball bearings used in liquid rocket engine turbopumps. This research experimentally investigated the friction coefficient of bearing materials via PTFE lubrication under cryogenic environment to clarify the friction characteristics of cryogenic turbopump ball bearings. These experiments revealed the dependence of the contact pressure on the friction coefficient. By several analyses, it was found that lower friction and better wear-resistance characteristics were caused by PTFE film that strongly adhered to metal fluoride formed on the surface of SUS440C due to moderate friction energy.

Effects of plasma treatments on the surface wettability properties of PTFE polymeric films

A cold cathode plasma source is constructed for modifying PTFE surface characteristics. The source was easily built, had a consistent plasma discharge medium and acceleration system. A cylindrical Langmuir probe is also used to evaluate plasma parameters like density, temperature or even plasma potential. This probe is designed to be moveable so that it may approach any desired position in the plasma volume. The influences of nitrogen pressure and probe-cathode gap on plasma parameters were investigated. The electron temperature [Formula: see text] fluctuated from [Formula: see text] to [Formula: see text][Formula: see text]eV as the pressure rises from 0.2 to 0.4[Formula: see text]mbar. Further, by increasing the cathode-probe gap from 0.4 to 2[Formula: see text]cm, the electron densities increased from [Formula: see text][Formula: see text]cm[Formula: see text] to [Formula: see text][Formula: see text]cm[Formula: see text]. Furthermore, the contact angles, work of adhesion and surface free-energy of pristine as well as irradiated PTFE films, were estimated. The results demonstrated that by extending the plasma exposure duration from 0 to 12[Formula: see text]min, the water contact angle is lowered from 82.2∘ to 30.5∘. At these conditions, the work of adhesion is raised from 81.9 to 134.1[Formula: see text]mJ/m2, as the surface free energy is increased from 29.8 to 71.8[Formula: see text]mJ/m2.

A Hybrid Triboelectric-Electromagnetic Nanogenerator Based on Arm Swing Energy Harvesting

As wearable devices continue to be updated and iterated, there is an increasing demand for energy supplies that are small, portable and capable of working continuously for extended periods of time. Here, a hybrid triboelectric-electromagnetic nanogenerator (HNG) based on a biomechanical energy harvester is demonstrated. The HNG is designed to be worn on the wrist according to the curve of the wearer’s arm swing. During the swinging of the arm, the magnet covered by the PTFE film will move relative to the curved cavity of the HNG and take on a negative charge by rubbing against the inner wall of the Cu coated cavity, resulting in a change in the potential difference between the two copper electrodes on the inner wall of the curved cavity. The movement of the magnet causes the magnetic flux of the three pairs of coils on both sides of the arc track to change to produce the induced electric potential, which converts the mechanical energy generated by the arm swing into electrical energy. After the rational design, the HNG is integrated into a small size device to achieve the collection of biomechanical energy. Several experiments were conducted to verify the HNG’s usability. Experiments show that the HNG takes 90 s to charge from 0 V to 1.2 V for a 1000 μF capacitor. In addition, the HNG can light up 23 LEDs simultaneously and provide a continuous supply of energy to portable electronic devices, such as temperature sensors and electronic watches after the capacitor has stored the energy. Furthermore, the HNG is experimentally verified by volunteers wearing the HNG to achieve continuous and stable output in all three states of slow swing, fast swing and running swing. This work not only provides a useful reference for human biomechanical energy harvesting, but can also provide a continuous, clean source of energy for wearable devices.

Experimental Investigation on the Failure Behavior of Single-Stiffened Composite Panels under Compressive Load

Whilst the thin-walled composite structures have been widely used to build the primary components in aircraft, Low-Velocity Impact (LVI) can cause severe intra-laminar and inter-laminar damage in the composite material, reducing the mechanical performance of these components. This paper presents an experimental study on the compressive failure behavior of a Single Hat-Stiffener Panel (SHSP) with two typical flaws, i.e., impact-induced damage and skin/stiffener debonding. LVI tests were performed to introduce the damage around the radius edge of the stiffener and the center of the flat skin panel, respectively, while the skin/stiffener debonding was introduced to the SHSP by artificially embedding a PTFE film at the skin/stiffener interface during autoclave curing. The impact energy to cause Barely Visible Impact Damage (BVID) was determined to be 22 J for the thin SHSP configuration. Whilst the considerable damage area was detected by the ultrasonic scan for the thick SHSP at an energy level of 35 J, the impact-induced indentation was not visually detectable (<0.35 mm), indicating a high impact resistance of this thick SHSP. Compression After Impact (CAI) results showed a significant reduction (59.1%) in the ultimate compressive strength of the SHSP when the impact location was on the stiffener compared to the pristine specimen. However, this reduction is less significant (34.7%) when the damage resulted from the same impact energy in the flat skin panel. In this study, the presence of skin/stiffener debonding does not adversely influence the compressive strength of the thick SHSP, while this debonding flaw appears to cause a minor reduction in the compressive strength of the thin SHSP.

Relationship between water droplet motion and output characteristics in droplet-based electricity generator

Recently water droplet-based electricity generators (DEGs), which utilize triboelectricity between a droplet and a dielectric material, has a great attention. DEG generates an instantaneous high-power density despite its simple metal/dielectric/metal stack structure. In the DEG, the contact area between a droplet and a dielectric surface affects the output characteristics. We fabricated a DEG using a PTFE film as a dielectric material, measured the output voltage and evaluated the contact area in various dropping heights and positions. We demonstrated that the output peak voltage increased as the contact area increased related to spreading and rebounding of a droplet.

Why Teflon is so slippery while other polymers are not.

Polytetrafluoroethylene [PTFE (Teflon)] is a uniquely slippery polymer, with a coefficient of friction that is an order of magnitude lower than that of other polymers. Though known as nonsticky, PTFE leaves a layer of material behind on the substrate while sliding. Here, we use contact-sensitive fluorescent probes to image the sliding contact in situ: We show that slip happens at an internal PTFE-PTFE interface that has an unusually low shear strength of 0.8 MPa. This weak internal interface directly leads to low friction and enables transfer of the PTFE film to the substrate even in the absence of strong adhesion.

Thermoradiationally Modified Polytetrafluoroethylene as a Basis for Membrane Fabrication: Resistance to Hydrogen Penetration, the Effect of Ion Treatment on the Chemical Structure and Surface Morphology, Evaluation of the Track Radius.

A study of the properties of thermoradiationally modified polytetrafluoroethylene and its importance for use as the basis of polymer membranes is presented. The hydrogen permeability of a TRM-PTFE film was studied in comparison with an original PTFE film, and showed a three-fold decrease in hydrogen permeability. Further, TRM-PTFE films were irradiated with accelerated Xe ions with an energy of 1 MeV with fluences from 1 × 108 to 1 × 1011. The changes induced by ion treatment were analyzed by infrared spectroscopy of disturbed total internal reflection (IR-ATR) and by atomic force microscopy (ASM). IR-ATR indicated the absence of destruction in the fluence range from 1 × 108 to 3 × 1010 cm-2 (in the area of isolated tracks) and the beginning of overlap of latent tracks on fluences from 3 × 1010 to 1 × 1011 cm-2. Topographic images with AFM showed layered lamellar structures that collapsed at a fluence of 108 cm-2. The destruction was accompanied by a decrease in roughness about seven times the size of the track core observed by the ASM method, fully corresponding to the value obtained on the basis of calculations using modeling in an SRIM program.

Towards Tough Thermoplastic Adhesive Tape by Microstructuring the Tape Using Tailored Defects

This paper presents a strategy towards achieving thermoplastic adhesive tapes with high toughness by microstructuring conventional tapes using tailored defects. Toughened tape was manufactured using two layers of a conventional tape where the bondline between the two adhesive layers was microstructured by embedding tailored defects with specific size and gap between them using PTFE film. Mode I toughness of the toughened tape was characterized experimentally. A high-fidelity finite element model was implemented to describe the toughening mechanisms using double cantilever beam simulations and end notch flexural tests. The model considers for the plasticity of the adhesive layer, the decohesion at the adherend-adhesive and adhesive-adhesive interfaces and progressive damage inside the adhesive layer. The adhesive-adhesive interface with the tailored defects inside the adhesive layer enables crack migration between adherend-adhesive interfaces, crack propagation at adhesive-adhesive interface, backward crack propagation under the defect, and plastic deformation of the adhesive ligament. The maximum toughness improvement of the tape with tailored defects of equal width and gap between two successive defects of 2 mm reached 278% and 147% for mode I and II, respectively, compared to conventional tape.