Polytetrafluoroethylene Films Research Articles

Effect of blind-bolt repair method on vibration and compression characteristics of delaminated composite aircraft panels

The paper investigates the validity and reliability of the blind-bolt repair method for repairing delaminated composite aircraft panels. The delaminated specimens are prepared by inserting Teflon films during the manufacturing process to simulate interlayer damage. Subsequently, these specimens are repaired using the blind-bolt method. Modal and uniaxial compression tests are conducted to quantitatively evaluate the natural frequency, mode shape and load-bearing strength of both delaminated and bolt-repaired specimens. Digital image correlation and ultrasonic phased array techniques are employed to characterize buckling instability and damage evolution of specimens. The results reveal that the natural frequency and compressive buckling strength of delaminated specimens significantly decrease. The mode shape also changes nonlinearly with the stiffness reduction. This variation is proportional to the size and the quantity of delaminations. The blind-bolt repair method effectively restores the vibration and mechanical properties of the delaminated composite structure by reconnecting separated sub-laminates. A repair tolerance of 20 mm–60 mm is recommended for a single blind-bolt. When the delamination length is 35 mm, the repair efficiency for the critical buckling load and the ultimate load is the highest, at 58.3% and 64.4%, respectively.

Natural Glycyrrhizic Acid‐Tailored Nanoparticles toward the Enhancement of Pesticide Bioavailability

AbstractPesticide spraying serves as a prevalent segment in crop production for substantial economic and ecological benefits. Nevertheless, the existing pesticide formulations are often plagued by droplets rebounding during the spraying process, and the controlled‐release, photolysis protection, and non‐targeted bio‐friendliness are not inadequately considered. Herein, by combining spinosad (SSD, a model pesticide) with glycyrrhizic acid (GL) as an attractive building block, a supramolecular co‐assembly strategy is employed to elaborate pesticide formulations (GL‐SSD) simultaneously featuring high deposition, controlled‐release, and environmental friendliness. The resulting spherical GL‐SSD nanoparticles (NPs) have an average diameter of 207 nm and show an improved 5.2‐fold photostability compared with commercial spinosad suspension (SSD SC). Upon impacting on hydrophobic surfaces of polytetrafluoroethylene film and cabbage leaf, the droplets of GL‐SSD NPs exhibit superior affinity to the micro/nano structure of the surface. Consequently, the droplet rebounding is inhibited effectively, ensuring high deposition efficiency of droplets on surfaces. In addition, the release of SSD from GL‐SSD NPs can be controlled by pH variation. Indoor toxicity and pot experiments demonstrate that GL‐SSD NPs possess good control efficacy against Plutella xylostella. The work offers an alternative approach for the development of multi‐functional and sustainable pesticide formulations with promising potentials in actual agriculture production.

Absorption of volatile organic compounds (VOCs) by polymer tubing: implications for indoor air and use as a simple gas-phase volatility separation technique

Abstract. Previous studies have demonstrated volatility-dependent absorption of gas-phase volatile organic compounds (VOCs) to Teflon and other polymers. Polymer–VOC interactions are relevant for atmospheric chemistry sampling, as gas–wall partitioning in polymer tubing can cause delays and biases during measurements. They are also relevant to the study of indoor chemistry, where polymer-based materials are abundant (e.g., carpets and paints). In this work, we quantify the absorptive capacities of multiple tubing materials, including four nonconductive polymers (important for gas sampling and indoor air quality), four electrically conductive polymers and two commercial steel coatings (for gas and particle sampling). We compare their performance to previously characterized materials. To quantify the absorptive capacities, we expose the tubing to a series of ketones in the volatility range 104–109 µg m−3 and monitor transmission. For slow-diffusion polymers (e.g., perfluoroalkoxy alkane (PFA) Teflon and nylon), absorption is limited to a thin surface layer, and a single-layer absorption model can fit the data well. For fast-diffusion polymers (e.g., polyethylene and conductive silicone), a larger depth of the polymer is available for diffusion, and a multilayer absorption model is needed. The multilayer model allows fitting solid-phase diffusion coefficients for different materials, which range from 4×10-9 to 4×10-7 cm2 s−1. These diffusion coefficients are ∼ 8 orders of magnitude larger than literature values for fluorinated ethylene propylene (FEP) Teflon film. This enormous difference explains the differences in VOC absorption measured here. We fit an equivalent absorptive mass (CW, µg m−3) for each absorptive material. We found PFA to be the least absorptive, with CW ∼ 105 µg m−3, and conductive silicone to be the most absorptive, with CW ∼ 1013 µg m−3. PFA transmits VOCs easily and intermediate-volatility species (IVOCs) with quantifiable delays. In contrast, conductive silicone tubing transmits only the most volatile VOCs, denuding all lower-volatility species. Semi-volatile species (SVOCs) are very difficult to sample quantitatively through any tubing material. We demonstrate a system combining several slow- and fast-diffusion tubing materials that can be used to separate a mixture of VOCs into volatility classes. New conductive silicone tubing contaminated the gas stream with siloxanes, but this effect was reduced 10 000-fold for aged tubing, while maintaining the same absorptive properties. SilcoNert (tested in this work) and Silonite (tested in previous work) steel coatings showed gas transmission that was almost as good as PFA, but since they undergo adsorption, their delay times may be humidity- and concentration-dependent.

A skin-wearable and self-powered laminated pressure sensor based on triboelectric nanogenerator for monitoring human motion

Flexible and skin-wearable triboelectric nanogenerators (TENGs) have emerged as promising candidates for self-powered tactile and pressure sensors and mechanical energy harvesters due to their compatible design and ability to operate at low frequencies. Most research has focused on improving tribo-negative materials for flexible TENGs, given the limited options for tribo-positive materials. Achieving biocompatibility while maintaining the sensitivity and capability of energy harvesting is another critical issue for wearable sensors. Here, we report a TENG-based biocompatible and self-powered pressure sensor by simple fabrication of layer-by-layer deposition methods. The Laminated Flexible-TENG comprises polytetrafluoroethylene (PTFE) and polymethyl methacrylate (PMMA) films embedded within a flexible and biocompatible polydimethylsiloxane (PDMS) matrix. A nanostructured PDMS surface obtained by oxygen plasma facilitated the sputter deposition of a layered indium tin oxide copper electrode and a tribo-positive PMMA thin layer on top. The addition of the indium tin oxide layer to copper significantly improved the quality and performance of the indium tin oxide-copper electrode. Self-powered Laminated Flexible-TENGs demonstrated impressive pressure-sensing capabilities, featuring dual sensitivity of 7.287 V/kPa for low pressure and 0.663 V/kPa for higher pressure. Moreover, the PDMS-encapsulated TENG sensor effectively traced the physiological motions, such as wrist and finger bending, and efficiently harnessed the waste energy from everyday physical activities, such as walking and jogging. The maximum peak-to-peak voltages of 18.3 and 57.4 V were recorded during these motions. Encapsulated TENGs have broad potential in wearable technology, including healthcare, human-machine interfaces, and energizing microelectronics.

Research on human gait sensing based on triboelectric nanogenerator

To address the problem of frequent battery replacement for wearable sensors applied to fall detection among the elderly, a portable and low-cost triboelectric nanogenerator (TENG)-based self-powered sensor for human gait monitoring is proposed. The main fabrication materials of the TENG are polytetrafluoroethylene (PTFE) film, aluminum (Al) foil, and polyimide (PI) film, where PTFE and Al are the friction layer materials and the PI film is used to improve the output performance. Exploiting the ability of TENGs to monitor changes in environmental conditions, a self-powered sensor based on the TENG is placed in an insole to collect gait information. Since a TENG does not require a power source to convert physical and mechanical signals into electrical signals, the electrical signals can be used as sensing signals to be analyzed by a computer to recognize daily human activities and fall status. Experimental results show that the accuracy of the TENG-based sensor for recognizing human gait is 97.2%, demonstrating superior sensing performance and providing valuable insights for future monitoring of fall events in the elderly population.

Macro-dipoles in soft/hard expanded-polytetrafluoroethylene + fluoroethylenepropylene (ePTFE + FEP) fluoropolymer-film systems for high-output piezoelectric ferroelectret-transducer applications

Multi-layer ferroelectrets consisting of fluoroethylenepropylene (FEP) copolymer and open-porous expanded polytetrafluoroethylene (ePTFE) films exhibit stable internal electret charges, high piezoelectric coefficients and heat resistance, making them promising candidates for wearable sensors or nanogenerators in body-area networks. Here, three- and five-layer (FEP/ePTFE/FEP and FEP/ePTFE/FEP/ePTFE/FEP) ferroelectret stacks were laminated and poled in a corona discharge. The resulting charge distributions were measured by use of the pulsed electro-acoustic (PEA) method and revealed that charges of opposite polarity were trapped at the interfaces between the FEP and ePTFE layers. Thus, the existence of one macro-dipole in the three-layer structure and of two macro-dipoles in the five-layer structure was directly shown for the first time. Moreover, electric-displacement-versus-electric-field (D-E) loops revealed that remnant polarization is given by the number of macro-dipoles in the respective stack. Due to the addition of the macro-dipoles, the piezoelectric d 33 coefficient of the FEP/ePTFE/FEP/ePTFE/FEP stack reaches 200 pC/N even under a potentially non-uniform compression of the soft ePTFE layers. The results should be useful for a better understanding and a performance optimization of ferroelectrets in self-powered intelligent devices.

Self-cleaning and amphiphobic properties of octadecyltrichlorosilane self-assembled modified polytetrafluoroethylene films

Self-cleaning and amphiphobic film has been widely used in daily life. To ensure good amphiphobic performance, simplify the production process, reduce cost and ensure environmental friendliness, the preparation process of the self-cleaning and amphiphobic film needs further optimization. In this study, with octadecyltrichlorosilane (OTS) and polytetrafluoroethylene (PTFE) powder as raw materials, a simple process and environmental pollution-free preparation method of self-cleaning and amphiphobic film was explored by spraying method. The structure of OTS@PTFE films was regulated by changing the ratio of PTFE to OTS. When the ratio was 4:10, the contact angle (CA) of the film’s surface to water reached 148°, and the surface energy was as low as 0.424 mJ·m−2. The OTS@PTFE film retained excellent amphiphobicity after 21 days of standing. When water dropleted roll on the film’s surface, they would carry away a large amount of pollutants and achieved self-cleaning effect. The coated OTS@PTFE film effectively reduced the surface energy of substrates such as stainless steel, glass and aluminum sheet, and the sprayed glass even actualized superhydrophobic. This confirmed the excellent versatility of OTS@PTFE films.

A triboelectric nanogenerator based on CNC/gelatin for running and jumping training monitoring

In this work, we proposed a triboelectric nanogenerator (TENG) based on cellulose nanocrystal (CNC)/gelatin composite film (CG-TENG) to monitor the posture and movements of athletes during jumping training. The triboelectric layers comprise a polytetrafluoroethylene film (which carries a negative charge) and a CNC/gelatin composite film (manifesting a positive charge). The CNC is derived from recycled wasted boxes using the traditional sulfuric acid hydrolysis method and is incorporated into the gelatin film as a nanoscale additive. By utilizing an external load resistance measuring 20 MΩ, it is possible to attain an all-time high instantaneous power of 583 µW. The electrical output of the CG-TENG demonstrates notable stability and endurance, as it maintains a consistent pattern during a duration of more than 30 000 cycles. By capitalizing on sustainable and green materials, the CG-TENG paves the way for innovative sports monitoring solutions, amplifying the potential for human physiological signal tracking.

Optical control of degradation of polytetrafluoroethylene films and its modification under electron irradiation

A method for monitoring the degradation of the optical density in polytetrafluoroethylene films and its modification, a copolymer of tetrafluoroethylene and ethylene, irradiated by electrons with energies of 100 keV and 10 MeV is described. The method is based on measuring the optical density of irradiated films in the photon energy range of 1-6 eV and is confirmed by established «dose-optical absorption» relationships. In particular, using the described method, a completely different nature of the radiation degradation of the optical properties of the two types of films under study was discovered. With an increase in the irradiation dose, «bleaching effect» in the region of 2-5 eV and the appearance of an absorption band at 5.6 eV are observed in polytetrafluoroethylene films. With a similar dose increase, three absorption bands at 4.0, 4.6 and 5.5 eV appear and grow in films of copolymer of tetrafluoroethylene and ethylene. The evidence of the critical role of the optical density of films in the functioning of space technology devices is given.

Performance of delaminated CFRP composite under pure bending using two-dimensional digital image correlation

ABSTRACT Delamination is an interlaminar damage which may be pre-existing in multilayered fibre reinforced polymer composite parts due to manufacturing imperfections or generated by out of plane loading during service life. Its existence leads to significant reduction of structural integrity, strength and stiffness of the material. Hence, to study the effect of induced delamination on the performance of a composite under pure bending, a circular polytetrafluoroethylene (PTFE) film was introduced between the second and third plies of a sixteen layered carbon/epoxy laminate during fabrication. The bending tests were conducted in displacement control mode. The displacements and strains were measured through the thickness of the composite using two-dimensional digital image correlation. The damage modes were captured using CCD camera and the causes were explained. The flexural strength and modulus of composite were 329.74 MPa and 104.58 GPa respectively. The delaminated composite behaved as a single member without any crack within the elastic range. The existence of PTFE drastically reduced flexural stiffness of composite beyond the stress at 75.81% of its ultimate strength. The ± 45º plies offered low mechanical performance against the induced off axis loading. Hence, in these plies fibre breakage was higher. In the portion of PTFE, the strains were higher due to larger outward displacements produced by local buckling.

Triboelectric nanogenerator-embedded intelligent bearing with rolling ball defect diagnosis via signal decomposition and automated machine learning

Smart fault diagnosis of bearings is of great significance due to their extensive applications on various occasions. Recently, self-powered sensing technology based on triboelectric nanogenerators promotes the development of intelligent bearings. However, the effective detection and recognition of the rolling element defects of bearings need to be investigated further. This study proposes a triboelectric sensor-embedded rolling bearing (T-bearing) to monitor the working conditions and conduct the defect diagnosis of rolling balls. The interdigitated copper electrode covered by polytetrafluoroethylene film is attached to the inner surface of the outer ring of a commercial bearing. Such a design not only directly forms the TENG with rolling balls to obtain the contact-sensing signals, but also successfully achieves the diagnosis of rolling ball defects with similar triboelectric signals through a novel analysis and prediction paradigm combining signal decomposition and automated machine learning. Finally, a recognition accuracy of 99.48% with five different conditions of bearing balls is reached, which is extremely superior to the highest accuracy of 78.34% without signal decomposition. Thus, this study provides a new strategy for the defect diagnosis and the intelligent application of triboelectric bearings.

Innovative design: Flexible conductive natural rubber electrode sheets with triboelectric generator activated by wheel rotation

Efficient consumption and clean energy management play a vital role in green energy. To be a part of this effort. Among the materials explored, flexible conductive electrodes utilizing triboelectric phenomena and unique properties of natural rubber composites have demonstrated a great potential for mechanical-to-electrical energy conversion. Fabrication process involves modifying natural rubber latex by incorporating conductive fillers such as carbon black, Ketjen black, and multiwall carbon nanotubes. The modified flexible conductive natural rubber sheets (CNRs) are then characterized for their structural and electrical properties. This structural arrangement significantly reduces the electrical resistance of the NR sheets. The incorporation of the MWCNT fillers leads to an increase in dielectric constant of CNRs. These properties are optimized via a proper design of the conductive natural rubber sheet triboelectric nanogenerator (CNRS-TENG). To enhance charge accumulation, polytetrafluoroethylene (PTFE) film is applied to the bottom surface of the CNRs. The CNRS-TENG are integrated into a wheel rotation generator setup. The output performance of the wheel rotation generator is influenced by the rotational speed as well as the arrangement of phases and segments. This work demonstrates that CNRs can be integrated with flexible electronic and other energy harvesting devices, opening possibilities for multifunctional clean energy solutions.

Robust, breathable, and chemical-resistant polytetrafluoroethylene (PTFE) films achieved by novel in-situ fibrillation strategy for high-performance triboelectric nanogenerators

Robust, breathable, and chemical-resistant polytetrafluoroethylene (PTFE) films achieved by novel in-situ fibrillation strategy for high-performance triboelectric nanogenerators

A multifunctional hydrogel-based strain sensor and triboelectric nanogenerator for running monitoring and energy harvesting

Recently, flexible wearable electronics for human running posture monitoring and human energy harvesting have attracted widespread attention. Hence, we design a mixed type conductive hydrogel based on polyvinyl alcohol, cotton paper, graphite oxide, and MXene, named PCGM hydrogel. Furthermore, the PCGM hydrogel can act as the PCGM-based strain sensor and triboelectric nanogenerator (P-TENG) for running posture monitoring and mechanical energy harvesting. The PCGM-based strain sensor has two sensing linear regions: The pressure sensitivity is 0.0164 kPa−1 in the low pressure region (0–16 kPa), whereas it is 0.002 86 kPa−1 in the high pressure region (16–120 kPa). To achieve comprehensive health monitoring of runners, the PCGM-based strain sensors can be installed on human joints and facial skin to monitor human posture and facial expressions. The PCGM hydrogel can be combined with a polytetrafluoroethylene film to form a P-TENG device for mechanical energy harvesting. The P-TENG maximum output power can reach 135 µW with a 30 MΩ load. The short-circuit current (Isc), open-circuit voltage (Voc), and transfer charge (Qsc) of P-TENG can reach 10.36 µA, 229.85 V, and 49.24 nC, respectively. This research provides an effective approach for human-running motion monitoring by using multifunctional flexible devices.

Determination of scattering and Urbach absorption contributions to the light extinction in PTFE films by using graphical representation technique and numerical solution of the inverse problem

Ellipsometrically obtained spectral dependences of ordinary αxy and extra-ordinary αz extinction/attenuation coefficients within the spectral range λ = 300…980 nm of uniaxially anisotropic polytetrafluoroethylene (PTFE) films were analyzed. We considered the capabilities and specific features of the graphical representation technique for determining the contribution of Rayleigh scattering and Urbach absorption to light attenuation in the spectral range beyond fundamental absorption. It has been shown that the graphical approach enables to estimate these contributions qualitatively, semi-quantitatively or quantitatively, depending on the situation. The conclusions made using the analysis of graphical representation are confirmed by numerical solution of the inverse problem via simulation of the αxy (λ), αz (λ) experimental dependences within the framework of a best-fit procedure. Being based on both of these approaches, we have ascertained that, in the as-prepared PTFE films, the so-called anomalous light scattering (ALS) with the spectral dependence of scattering coefficient αs ≈ as λ–p (p > 4) takes place. Transformation of scattering from ALS to the Rayleigh one with p ≈ 4 due to annealing is accompanied by an increase of Urbach (subband) absorption. Both of these factors cause narrowing the dynamic range of extinction coefficient values. Both scattering and absorption coefficients are higher for the component of light polarized along the normal to the substrate as compared to the component polarized in parallel to it. The relationship between observed behavior of the scattering and absorption coefficients and the film structure has been discussed.

Self‐Adaptive Colored Radiative Cooling by Tuning Visible Spectra

Traditional radiative cooling leads to overcooling in the winter season and increases the total energy consumption of buildings. And, the super white color limits its practical applications. In this work, a bilayer coating consisting of a polydimethylsiloxane (PDMS)@thermochromic dye film as the top layer and a super white polytetrafluoroethylene film as the bottom layer is designed to achieve self‐adaptive colored radiative cooling by tuning visible spectra. The mass ratio of PDMS to the black thermochromic dye is 1: 0.04 to balance the solar heating and radiative cooling performances although the thermal emittance is constant (0.95). The designed black adaptive coating can achieve modulations of visible and solar reflectance from 0.36 to 0.91 and from 0.62 to 0.92, respectively. And its net power can switch from 331 W m−2 at −10 °C for heating to 70 W m−2 at 50 °C for cooling down. In the indoor and outdoor experiments, it is shown that adaptive coatings can achieve heating performance in a cold environment while cooling performance in a hot environment. Further energy consumption calculation indicates that adaptive coatings can save 5%−44% of energy consumption in different climates. Various colors and critical transition temperatures can be regulated by different thermochromic dyes for various scenarios.

Super-Low Friction Electrification Achieved on Polytetrafluoroethylene Films-Based Triboelectric Nanogenerators Lubricated by Graphene-Doped Silicone Oil.

The novel proposal of Wang's triboelectric nanogenerator (TENG) has inspired extensive efforts to explore energy harvesting devices from the living environment for the upcoming low-carbon society. The inevitable friction and wear problems of the tribolayer materials become one of the biggest obstacles for attaining high-performance TENGs. To achieve super-low friction electrification of the TENGs, the tribological and electrical behaviors of the sliding-mode TENGs based on polytetrafluoroethylene (PTFE) films and metallic balls under both dry friction and liquid lubrication conditions were investigated by using a customized testing platform with a ball-on-flat configuration. Most interestingly, a super-low friction coefficient of 0.008 was achieved under graphene-doped silicone oil lubrication. The corresponding wear rate of the PTFE film was drastically decreased to 8.19 × 10-5 mm3/Nm. Simultaneously, the output short-circuit current and open-circuit voltage were enhanced by 6.8 times and 3.0 times, respectively, compared to the dry friction condition. The outstanding triboelectrical performances of the PTFE film when sliding against a steel ball are attributed to the synergistic lubricating effects of the silicone oil and the graphene nanosheets. The current research provides valuable insights into achieving the macro-scale superlubricity of the TENGs in practical industrial applications.

Influence of PTFE-Based Dry Lubricants on Friction and Wear Behavior in Dry Lubricated Steel–Bronze Contact

Abstract In this article, solid lubricants are investigated to examine their tribological performance in a dry lubricated steel–bronze contact. The examined solid lubricants are made of polyamide (PA) and irradiated polytetrafluoroethylene (PTFE), which are chemically bonded by reactive melt extrusion. For the tribological investigations, a block-twin-disc test rig, on the one hand, and a three-disc test rig, on the other hand, were used under ambient conditions, where the solid lubricant for lubricating the steel–bronze contact was released from a block or a disc. Results from the tribological investigations are presented here, showing the friction and wear behavior in a steel–bronze contact depending on the slide-to-roll ratio in the contact between the steel disc and the compound body. Furthermore, surface analytical investigations on the steel and bronze discs were carried out. These studies showed that the chemical bonding of 20 wt% of irradiated PTFE in PA12 improves the wear and friction behavior in steel–bronze contact significantly, due to the buildup of a transfer film of PTFE on the steel surface.

Damage formation and evolution mechanisms in drilling CFRP with prefabricated delamination defects: Simulation and experimentation

Delamination is a common defect in carbon fiber reinforced polymer (CFRP) during the molding process. Accurately understanding the formation and evolution mechanisms of drilling damage in CFRP with delamination defects is helpful for effectively suppressing drilling defects with delamination. In this study, a macro-micro finite element model (FEM) of CFRP with prefabricated delamination defects during drilling is established to simulate and analyze the damage formation and evolution behavior. The circular polytetrafluoroethylene (PTFE) films are employed to simulate the delamination defects in CFRP. These samples with different sizes of prefabricated delamination defects are prepared for the drilling experiments. The results show that the maximum errors of the thrust force and the exit damage factor between the simulation and experiments are 8.75% and 4.2% respectively, indicating good reliability of the simulation model. Under the condition of CFRP with delamination defects, as the size of the delamination defects increases, the maximum thrust force decreases, while the maximum delamination propagation length and exit damage increase. Compared to the case without delamination defects, when the delamination diameter is 7 mm, the delamination propagation percentage and the maximum stress in CFRP increase by 52.17% and 155.4% respectively, and the maximum increment of the exit delamination damage factor is 38%.

Enhancing Adhesion between Polyphenylene Sulfide Fabric and Polytetrafluoroethylene Film for Thermally Stable Air Filtration Membrane

Enhancing Adhesion between Polyphenylene Sulfide Fabric and Polytetrafluoroethylene Film for Thermally Stable Air Filtration Membrane