Polytetrafluoroethylene Electret Research Articles

Contact-Electro-Catalysis Through Electret Behavior to Facilitate Electron Transfer.

Contact-electro-catalysis (CEC) usually uses polymer dielectrics as its catalysts under mechanical stimulation conditions, which although has a decent catalytic dye degradation effect still warrants performance improvement. A carrier separation promotion strategy based on an internal electric field by polarization can effectively improve ferroelectric material performance in photocatalysis and piezocatalysis. Therefore, carrier separation as a necessary process of CEC also can be promoted and is largely expected to improve CEC performance theoretically. However, the carrier separation enhancement by the internal electric field strategy has not been achieved in the CEC experiment yet, because of the difficulty of building an internal electric field in an inert polymer dielectric. Herein, a polytetrafluoroethylene (PTFE) dielectric was charged through an electret process, which was believed to establish an internal electric field for CEC catalysts proved by KPFM, XPS, and triboelectric nanogenerator voltage output analysis. The fastest degradation rate of methyl orange reached over 90% at 1.5 h, while the hydroxyl free radical (•OH) yield of the PTFE electret was nearly three times that of the original PTFE. Density functional theory (DFT) calculations verified that the potential barrier of interatomic electron transfer between PTFE and H2O was reduced by 37% under the internal electric field. The electret strategy used herein to optimize the PTFE catalyst provides a base for the use of other general plastics in CEC and facilitates the production of easily prepared, easily recyclable, and inexpensive polymer dielectric catalysts that can promote large-scale pollutant degradation via CEC.

Fabrication and characteristics of electret ultrasonic‐sensor using laser patterning

AbstractIn this study, in an electret capacitor sensor (ECS), which is an electromechanical exchange device consisting of an electret sandwiched between two electrodes, ridges as spacers and grooves as gaps were formed in the PTFE (polytetrafluoroethylene) layer of the insulating electrode by laser ablation. The ECSs were then fabricated using PTFE electrets, and the charge retention and airborne ultrasonic wave transmitting and receiving characteristics were investigated. The charge retention characteristics of the ECS with laser‐patterned insulating electrodes were slightly lower than those of the silica‐aggregate electret. As the thickness of the insulating layer increased or the groove width decreased, the transmitting and receiving sensitivity increased significantly and then peaked and degraded at the measurements of transmitting and receiving. The ECS with the highest peak sensitivity obtained by laser patterning had a bandwidth comparable to that of the conventional ECS with silica aggregate electret, but the peak sensitivity was improved by up to 8 dB. Therefore, laser patterning could contribute to the improvement of ECS performance.

Surface potential uniformity and sensitivity of large-area PTFE electret discs of different thicknesses produced by a modified corona poling rotating system for dosimetry applications

In this study, large-area (6-cm diameter) Teflon polytetrafluoroethylene (PTFE) discs of different thicknesses (0.2-, 0.5- and 1 -mm) were negatively and positively charged by using the “modified single point-to-plane corona poling rotating system”. The effects of some crucial parameters of the PTFE disc as well as the modified corona poling rotating system on the PTFE surface potential uniformity such as: (a) PTFE disc thickness, (b) PTFE disc polarity and (c) needle-to-PTFE disc distance were successfully reported. Accordingly, closer needle-to-PTFE disc distance, positive charging mode and thinner PTFE disc provided a better PTFE surface potential uniformity. However, the effects of PTFE charge polarity and needle distance on the electrostatic charge potential uniformity were much more remarkable in comparison with the effects of PTFE thickness. Additionally, the surface potential distribution profiles of charged PTFE discs were totally flat and independent of the PTFE thickness at 5- and 13-[Formula: see text]mm needle distances for the negative and positive charging modes, respectively. At the optimized charging conditions, large-area PTFE electret disc (0.5-mm-thick) with positive uniform surface charge potential especially at the edges up to [Formula: see text] 1.8[Formula: see text]kV with stability up to 77 days studied was produced by applying a new multiple heat treatment protocol to the PTFE disc for radon dosimetry. As also observed in this study, the sensitivity of PTFE electret dosimeters to a defined radon gas concentration increases as the PTFE thickness increases. Meanwhile, 0.5-mm-thick PTFE electret disc produced was selected to be used as a high quality electret dosimeter with acceptable and superior parameters for different applications in particular medium-term radiation dosimetry in both low and high dose rate ionizing radiation fields.

Triboelectric charging of polytetrafluoroethylene antithrombotic catheters.

This study proposes that a polytetrafluoroethylene (PTFE) electret tube charged by frictional electricity can prevent the solidification of the indwelling catheter in blood vessels. Coagulation in intravascular indwelling catheters may discontinue the treatment because of thrombus-derived bacteria-adhesion infections or poor blood removal. Current commercially available intravascular catheters lack complete antithrombotic measures, even with heparin or urokinase antithrombotic coatings. Herein, we tested the effectiveness of an antithrombotic treatment that prevents coagulation using a static electric charge on the interior of the PTFE tube via the triboelectric effect by rubbing the tube's inner wall with a round glass rod. The anticoagulation properties were evaluated by enclosing a sample of blood in an electret tube and observing the coagulase adhering to the inner wall using a microscope. To confirm the effectiveness of this treatment, the charge-distribution on the inner surface of the electret tube was measured, surface irregularities were observed, and the elements on the surface were analyzed. The surface potential inside the electret tube was - 366.4V, which proved effective for an antithrombotic treatment, as it discouraged coagulation, and the triboelectric charging process caused neither surface element denaturation nor significant surface irregularities. The nearly uniform negative surface charge on the inside of the tube was responsible for the antithrombotic effect because no surface irregularities or change in the surface element denaturation was observed. Triboelectrically charged PTFE electret tubes are highly useful for intravascular indwelling catheters.

Tunable polytetrafluoroethylene electret films with extraordinary charge stability synthesized by initiated chemical vapor deposition for organic electronics applications

Bulk polytetrafluoroethylene (PTFE) possesses excellent chemical stability and dielectric properties. Indeed, thin films with these same characteristics would be ideal for electret applications. Previously, the electret properties of PTFE-like thin films produced by rf sputtering or plasma enhanced chemical vapor deposition were found to deteriorate due to structural changes and surface oxidation. In this article, the technique of initiated chemical vapor deposition (iCVD) is evaluated for electret applications for the first time. The iCVD method is known for its solvent-free deposition of conformal, pinhole-free polymer thin films in mild process conditions. It is shown that PTFE thin films prepared in this way, show excellent agreement to commercial bulk PTFE with regard to chemical properties and dielectric dissipation factors. After ion irradiation in a corona discharge the iCVD PTFE thin films exhibit stable electret properties, which can be tailored by the process parameters. Due to the mild deposition conditions, the iCVD technique is suitable for deposition on flexible organic substrates for the next-generation electret devices. It is also compatible with state-of-the-art microelectronic processing lines due to the characteristics of conformal growth and easy scaling up to larger size substrates.

Surface potential stability of large-area Teflon PTFE electret dosimeters of different thicknesses

The effects of charge polarity and thickness on the surface charge potential stability responses of large-area Teflon polytetrafluoroethylene (PTFE) discs electrostatically charged by a new “modified single point-to-plane corona poling rotating system” were studied. Large-area Teflon discs (6 cm diameter) with 0.2, 0.5 and 1 mm thicknesses were used to produce both negatively or positively charged Teflon discs, at the same charging conditions. The deposited charge potential stability of the Teflon discs of different thicknesses monitored by a non-contacting electrostatic voltmeter for an extended time were monitored up to 77 days. Some inter-related parameters such as surface charge potential and external electrostatic field, internal electrostatic field, surface charge density, and the storage duration were also studied. The thick large-area Teflon disc electrets produced provided a steady-state charge stability on either negative (0.2, 0.5 and 1 mm thick) or positive (1 mm thick) surface charge potentials for the long period studied. The Teflon electret discs produced demonstrated having the highest charge potential stability in thicker electrets (1 mm), either negative or positive polarity, with provision of high potential for different applications in general and radiation protection dosimetry in particular.

Single‐Electrode, Nylon‐Fiber‐Enhanced Polytetrafluoroethylene Electret Film with Hollow Cylinder Structure for Mechanical Energy Harvesting

AbstractA single‐electrode nylon fiber‐incorporated polytetrafluoroethylene (PTFE) electret flexible film with hollow cylinder structure is developed for enhanced mechanical energy harvesting. The power is generated by the nylon fiber/PTFE electret film via bending deformations that result in charges transferring between the conductive carbon black silicone rubber (CBS) electrode and ground. The results demonstrate that the nylon fiber/PTFE electret film results in enhanced open‐circuit voltage, Voc, (about 0.45 times more) compared to a pure PTFE based on the hollow cylinder structure. With the step‐increased distance of travelling for the reported hollow cylinder structure device, more power is generated by this mechanical‐electrical energy conversion because of a greater deformation compression onto the nylon fiber/PTFE electret film. The peak of the generated short‐circuit current, ISC, and Voc based on the nylon fiber/PTFE electret film with 1 m s−2 are up to 0.35 μA and 72 V, respectively. It is also possible to light an 8 light‐emitting diode (LED) setup by finger tapping, demonstrating the good mechanical energy conversion performance of the nylon fiber/PTFE electret film. Moreover, a quick voltage response of the nylon fiber/PTFE electret film is demonstrated in several different ultrasonic environments (such as 70 kHz and 30 kHz).

Suspended polytetrafluoroethylene nanostructure electret film in dual variable cavities for self-powered micro-shock sensing

We report a suspended polytetrafluoroethylene (PTFE) nanostructure electret film in dual variable cavities for a self-powered micro-shock sensing application. The prototype contained series variable air cavities, a suspended nanostructure PTFE electret film and independent electrode films. The charges on the suspended nanostructure PTFE electret film provided the electrostatic field around the electret film in the series variable air cavities. When the reported device was driven by a micro-shock pressure, the inducted electrostatic charges on both the top and bottom electrodes would vary as the micro-shock pressing or releasing. Experimental results showed that the maximum of a short-circuit current density (Jsc) and an open-circuit voltage (Voc) reached 3 ± 0.1 nA cm−2 and 3.6 ± 0.1 V, respectively. It was found that the parameter Jsc was more advantageous in identifying stronger shocks (parameter acceleration a bigger than 0.1 m s−2), whereas the parameter Voc was more sensitive for weaker shocks, such as acceleration a smaller than 0.1 m s−2. Moreover, finger continuous micro-shock pressure taps application was used to demonstrate the mechanical energy conversion performance with 4.5 ± 0.2 V open-circuit voltages. The research on the nanostructure electret PTFE film in series dual variable air cavities not only gave us a fresh idea about the principle and design of the shocking sensor, but also provided an easy fabrication and a low cost shocking sensor for the Internet of Things (IoT) systems.

A novel high-sensitivity electrostatic biased electric field sensor

In this paper, an electric field sensor (EFS) with high sensitivity is proposed for low-frequency weak-strength ac electric field (E-field) measurements. The EFS is based on a piezoelectric cantilever biased by a strong electrostatic field. The electrostatic bias can enhance the electric field force of a weak ac E-field, thus the cantilever can oscillate in a weak ac E-field and the device sensitivity improves. Theoretical analyses have been established and suggest that a stronger strength of electrostatic field bias would produce a higher sensitivity improvement. In the experiment, a demonstrated sensor consisting of a polyvinylidene fluoride (PVDF) piezoelectric cantilever and a polytetrafluoroethylene (PTFE) electret was built and tested. Instead of extra voltage sources, the PTFE electret was charged to provide the electrostatic field, allowing the EFS a low energy consumption and a simple electric circuit design. The experiment results show good agreement with the simulation. The sensitivity of the cantilever E-field sensor reached 0.84 mV (kV/m)−1 when the surface potential of the electret was −770 V.

Silicon based polytetrafluoroethylene electrets: Preparation and corona charging characteristics

Abstract In this paper, silicon based planar technology and high performance fluorocarbon polymer polytetrafluoroethylene (PTFE) are combined to achieve PTFE thin film electrets on wafer. The PTFE film is fabricated onto SiO2 substrates and Pt substrates using spin coating and annealing processes, and its electret effect is demonstrated using negative corona charging method. PTFE electrets with different surface morphology exhibit different charge storage capability. Maximally, surface potential of −396 V is achieved on Pt substrates and −361 V is achieved on SiO2 substrates. The average retain rate of surface potential over 240 h is 90.6% for Pt substrates and 76.3% for SiO2 substrates. The proposed method presents the primary step toward integrated electrostatic devices.

Stabilization of positive charge on polytetrafluoroethylene electret films treated with titanium-tetrachloride vapor

The surface of polytetrafluoroethylene films was treated with titanium-tetrachloride vapor. The treatment was carried out in a flow reactor by means of molecular-layer deposition, a method from the arsenal of chemical nanotechnology. X-ray photoelectron spectroscopy reveals that such a treatment results in considerable changes in the chemical composition at and near the surface of the fluoropolymer film. Both, defluorination and oxidation of the surface were observed. At the same time, samples treated with titanium tetrachloride show a significant enhancement in the thermal stability of the positive homocharge. The thermally stimulated surface-potential-decay curves were observed to shift to higher temperatures by more than 100 °C

Thermal stability of piezoelectricity for porous polytetrafluoroethylene electret film

In this paper, the thermal stability of piezoelectricity of porous polytetrafluoroethylene electret film prepared by unidirectional stretching at suitably high temperature is studied. A very good thermal stability of the piezoelectric coefficient of the porous electret film was found by measuring the surface potential decay, analyzing the open-circuit thermally stimulated discharge current spectra and the elastic modulus as a function of temperature, as well as by investigating the quasi-static piezoelectric coefficient under different conditions. The experimental results point out that the thermal stability of the piezoelectric coefficient depends on both the thermal stability of space charge stored in functional film and the thermal stability of its mechanical properties such as the elastic modulus of the material. The results demonstrate that the continuous service temperature region of the functional devices made of porous electret films is expanded due to their thermal stability.

PTFE electret negative charge stability after RF plasma treatment

An 18 μm nonmetallized polytetrafluoroethylene (PTFE) film is treated in radio frequency (RF) plasma before a point-to-grid corona charged. The isothermal (170°C) surface potential measurement shows that the surface charge stability is significantly dependent on the plasma sources and treatment conditions. Oxygen (O2), oxygen/helium (O2/He) mixture gases and helium (He) plasma treatment enhance the film negative charge stability significantly but not hydrogen (H2) plasma. Electron spectroscopy chemical analysis confirms that this superior negative charge retention for O2 plasma treatment is a result of the high concentration of oxide groups on the subsurface during the plasma treatment.

Polymer electret guidance channels enhance peripheral nerve regeneration in mice

Polytetrafluoroethylene (PTFE) tubes were prepared as electrets displaying a quasi-permanent surface charge due to the presence of trapped monopolar charge carriers. PTFE tubes containing either positive or negative charges and electrically neutral PTFE tubes were used as nerve guidance channels for the repair of a 4mm nerve gap in the sciatic nerve of mice. After 4 weeks of implantation, positively and negatively charged PTFE electrets contained regenerated nerves with significantly more myelinated axons than nerves regenerated in uncharged PTFE tubes. This observation suggests that peripheral nerve regeneration can be enhanced by electrically charged nerve guidance channels.

Modeling of thermally stimulated currents in polytetrafluoroethylene

A phenomenological model has been derived for thermally stimulated open-circuit current measured on negatively charged polytetrafluoroethylene electret film. The model is based on trap controlled release of negative charge carriers using approximations justified by thermally stimulated current and mean charge depth results. To describe the open-circuit current, a minimum of five traps was necessary including surface and bulk traps with activation energies of 1.3 (2), 1.4, 1.5, and 1.7 eV. In addition, attempt-to-escape frequencies were calculated and found in the range 1011–1013 s−1.