Polytetrafluoroethylene Films Research Articles

Urea-linked covalent organic framework functionalized polytetrafluoroethylene film for selective and rapid thin film microextraction of rhodamine B

Incorporation of highly selective and stable adsorbent with facile extraction technology is desired in practical analysis. Here we show the rational preparation of a urea-linked covalent organic framework functionalized polytetrafluoroethylene film (COF-117-PTFE) with ordered porous structure, rich functional groups, and large surface area-to-volume ratio as the effective adsorbent for convenient, selective and rapid thin film microextraction (TFME) of rhodamine B (RB). The COF-117-PTFE based TFME coupled with high performance liquid chromatography-fluorescence detector (HPLC-FLD) successfully realized the determination of RB with the limit of detection of 0.007 μg L−1, the linear range of 0.1 - 100 μg L−1. The relative standard deviation (RSD) of intraday (n = 5) and interday (n = 5) for the determination of 10 μg L−1 RB were 2.3% and 6.8%, respectively. The absolute recoveries were 80.3%, 71.2% and 67.9% in river water, chili powder and Sichuan pepper powder, respectively. The recoveries for RB spiking in complicated real samples (dry chili, chili powder, dry Sichuan pepper, Sichuan pepper powder and river water) ranged from 90.4% to 107.5%. The developed COF-117-PTFE based TFME-HPLC-FLD method is promising in practical application. This work reveals the high potential of functionalized COF film as the adsorbent for effective extraction of trace contaminants in complicated samples.

A Light-Powered Triboelectric Nanogenerator Based on the Photothermal Marangoni Effect.

The photothermal Marangoni effect enables direct light-to-work conversion, which is significant for realizing the self-propulsion of objects in a noncontact, controllable, and continuous manner. Many promising applications have been demonstrated in micro- and nanomachines, light-driven actuators, cargo transport, and gear transmission. Currently, the related studies about photothermal Marangoni effect-induced self-propulsion, especially rotational motions, remain focused on developing the novel photothermal materials, the structural designs, and the controllable self-propulsion modes. However, extending the related research from the laboratory practice to practical application remains a challenge. Herein, we combined the photothermal Marangoni effect-induced self-propulsion with the triboelectric nanogenerator technology for sunlight intensity determination. Photothermal black silicon, superhydrophobic copper foam with drag-reducing property, and triboelectric polytetrafluoroethylene film were integrated to fabricate a triboelectric nanogenerator. The photothermal-Marangoni-driven triboelectric nanogenerator (PMD-TENG) utilizes the photothermal Marangoni effect-induced self-propulsion to realize the relative motion between the triboelectric layer and the electrode, converting light into electrical signals, with a peak value of 2.35 V. The period of the output electrical signal has an excellent linear relationship with the light intensity. The accessible electrical signal generation strategy proposed here provides a new application for the photothermal Marangoni effect, which could further inspire the practical applications of the self-powered system based on the photothermal Marangoni effect, such as intelligent farming.

High-Sensitivity Multiresponses Cellulose-Based Actuators with Configurable Amplitude

Actuators have many applications in artificial muscles, soft robots, and optical switches. Herein, we designed and fabricated a multifunctional actuator using cellulose composites that can be driven by humidity, natural sunlight, and electrothermal processes. Highly conductive and flexible cellulose, MXene, and PEDOT:PSS composite (CMPC) films were prepared with a facile blending-vacuum filtration method. Benefiting from the high conductivity, the CMPC film exhibited excellent performance in electromagnetic shielding, electrothermal processes, and humidity detection. Moreover, due to the hygroscopic properties of cellulose, CMPC film shows a negative coefficient of thermal expansion, in contrast to typical polymer films. By depositing a hydrophobic polytetrafluoroethylene (PTFE) film onto the CMPC film, a two-layer actuator was developed. Owing to the opposite thermal expansion properties of CMPC and PTFE, the as-obtained actuators exhibit a high sensitivity, and are made into bionic flowers, worms, robots, and smart curtains, showing fast responses to humidity, natural sunlight, and electrothermal processes. In fact, natural sunlight of 80 mW cm–2 or a power supply of as low as 3 V can drive the actuator to a bending curvature of 2.85 cm–1, corresponding to a bending angle of 360°. The bionic robot is configurable with movements and speeds that can be controlled by a microcontroller and have a wide application in biological bionic and soft robots.

Determination on the thermal conductivity and thermal contact resistance of thin composite phase change films as a thermal interfacial material

Sub-millimeter thick phase change material (PCM) composites have been utilized in the thermal management of micro-electronics serving as a novel thermal interfacial material. However, there is a lack of appropriate measuring methods and precise data for the thin-film PCM composites' intrinsic thermal conductivity, as well as the thermal contact resistance (TCR) at interfaces between those thin-films and metal. In this work, the out-of-plane thermal conductivity of thin-film PCM35, which is a paraffin composite showing the melting point of 35 °C, was first gauged through the commercialized transient plane source (TPS) method, followed by a correction process to deduct the TCR between thin films/temperature sensor interfaces. The direct TPS readings were corrected based on the proportional relation between samples’ thickness and inherent thermal resistance. An improved steady-state heat flow apparatus designed for thin-walled samples was then utilized to examine the reliability of the corrected TPS technique, with a relative deviation between them being only ∼7%. In order to test the applicability of the corrected TPS method, the thermal conductivities of thin polytetrafluoroethylene films were also determined. Furthermore, the TCR between thin PCM35 film and thin 1060Al plate was identified by performing the improved steady-state apparatus. The contribution of overheated PCM35 film on fitting the interfacial voids and reducing the TCR were elucidated, which can guide the thermal design with the use of such thin-film PCMs.

Investigation of vibration and rotation multifunctional sensors based on the triboelectric effect

Studies show that to monitor the status of a rotating device accurately, vibration and rotation should be monitored simultaneously. In this regard and based on the effects of triboelectricity and electrostatic induction, a multifunctional sensor (MS) with a rotating-sleeve structure and two independent sensitive units is proposed in the present study. Nylon fabric and polytetrafluoroethylene film are used in the sensitive units, and the bounce of the copper ball on the sandwich elastic sensitive layer is used to determine the vibration level. Then theoretical analysis and finite element simulations are carried out to study the charge transfer characteristics of the sensor. It is found that the MS can truly reflect the vibration and rotation characteristics of the rotating device. Moreover, experiments are carried out and the obtained results show that the detection range of the sensor and its sensitivity are 0–36 m s−2, and 40.38 mV s2 m−1, respectively. It is concluded that the proposed MS can accurately identify the vibration frequency. The obtained results demonstrate that at rotation speeds of up to 2000 rpm, this MS can be used to measure the direction of rotation, speed, and angular acceleration with a relative error of less than 0.95%. Considering the superior characteristics of the proposed MS, it can be used to monitor the motion state of objects in real-time and has potential application prospects in the field of internet of things.

Transparent and flexible passivation of MoS2/Ag nanowire with sputtered polytetrafluoroethylene film for high performance flexible heaters

We demonstrated highly transparent and flexible polytetrafluoroethylene (PTFE) passivation for the MoS2/Ag nanowire (Ag NW) electrodes used in thin film heaters (TFHs). The electrical, optical, and mechanical properties of PTFE coated MoS2/Ag NW electrode were compared to the bare MoS2/Ag NW electrode to demonstrate effective passivation of the sputtered PTFE films before and after the 85 °C–85% temperature-relative humidity environment test. In addition, we investigated the performances of TFHs with PTFE/MoS2/Ag NW as a function of PTFE thickness from 50 to 200 nm. The saturation temperature (87.3 °C) of TFHs with PTFE/MoS2/Ag NW electrode is higher than that (61.3 °C) of TFHs with bare MoS2/Ag NW, even after the 85 °C–85% temperature-relative humidity environment test, due to effective passivation of the PTFE layer. This indicates that transparent PTFE film prepared by sputtering process provides effective thin film passivation for the two-dimensional (2D) MoS2 and Ag NW hybrid electrode against harsh environment condition.

Highly durable direct-current power generation in polarity-controlled and soft-triggered rotational triboelectric nanogenerator

While the sliding-mode triboelectric nanogenerators (TENGs) have demonstrated one of the most efficient rotational energy harvesting devices, alternating-current (AC) generation and wear-off have been a long-standing bottleneck for practical applications. Here, we developed a polarity-controlled and soft-triggered (P-S) TENG for highly efficient and durable direct-current (DC) power generation. The P-S TENG consists of polytetrafluoroethylene (PTFE), nylon, and Cu films for triboelectrification, as well as another Cu film for charge-delivering electrode. The PTFE and nylon films were alternately attached to the outer acrylic cylinder, and four-segmented Cu films were attached to the inner acrylic cylinder. The P-S TENG generated a power-density of 0.32 mW/cm2, which was 4-fold and 32-fold larger than that of paired alternate and single polarity TENG, respectively. Remarkably, the DC output of P-S TENG remained nearly constant, despite 372,000 rotations, which sharply contrasted with the substantial power decrease (47%) in hard-triggered TENG. This work provides an important advancement in a rotational TENG with high DC power generation and long-term durability.

Teflon graft poly N–N-dimethylacrylamide as a ciprofloxacin release system

This work presents the modification of Teflon films, formally named polytetrafluoroethylene, with dimethylacrylamide (DMA) through a graft copolymerization reaction initiated by gamma radiation (from Co-60) to endow the material with the capability to deliver hydrophilic drugs. Results suggest the surface of the grafted films is suitable for the load/release of ciprofloxacin, a broad-spectrum antibiotic, achieving the goal of the study. The analysis was supported by water sessile drop contact angles and swelling in water and phosphate buffers. Characterization of grafted films was completed by attenuated total reflectance infrared spectroscopy (FTIR-ATR), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC).

Polytetrafluoroethylene Modified Nafion Membranes by Magnetron Sputtering for Vanadium Redox Flow Batteries

Commercial Nafion membranes have been widely used for vanadium redox flow batteries (VRFB) but with relatively low ion selectivity. A chemical method is commonly employed to modify the organic membranes, whereas physical approaches are rarely reported in view of less compatibility with the organic species. In this study, an ultrathin polytetrafluoroethylene (PTFE) film of less than 30 nm is deposited onto the Nafion substrates by radio frequency magnetron sputtering to form PTFE@Nafion composite membranes. The PTFE layer of hydrophobic and inert feature enhances the dimensional stability and the ion selectivity of the Nafion membranes. The VRFB single cell with an optimized composite membrane exhibits a better self-discharge property than that of the Nafion 212 (i.e., 201.2 vs. 18.6 h), due to a higher ion selectivity (i.e., 21.191 × 104 vs. 11.054 × 104 S min cm–3). The composite membranes also show better discharge capacity retention than the Nafion 212 over the entire 100 cycles. The results indicate that the magnetron sputtering is an alternative and feasible route to tailor the organic membranes via surface modification and functionalization.

Broadband terahertz guided-mode resonance filter using cyclic olefin copolymer.

We propose an all-dielectric single-layer guided-mode resonance filter (GMRF) operating in the high-frequency terahertz (THz) region. For the fabrication of thin gratings to achieve strong resonance in the high-frequency region, the refractive index and absorption must be small, while the tensile strength must be high. Cyclic olefin copolymer (COC) films have a lower refractive index and absorption than polyethylene terephthalate (PET) films and a higher tensile yield strength than polytetrafluoroethylene (PTFE) films. Therefore, the COC film was found suitable to fabricate a GMRF operating in the high-frequency THz region. We fabricated COC-based single-layer GMRFs with a thickness of 50 µm and grating periods of 500, 400, 300, 200, and 100 µm; the resonance frequencies of the TE0,1 mode were 0.576, 0.712, 0.939, 1.329, and 2.759 THz, respectively. A shorter grating period caused a greater shift of the resonance to a higher frequency. In particular, the COC film enabled the fabrication of a 100-µm grating period with a ridge width of 32 µm and length of 2 mm, enabling the GMRF to operate up to 2.759 THz, which is very high frequency compared to the previous highest frequency of 0.7 THz. These results were in good agreement with a simulation using rigorous coupled-wave analysis.

The effect of carbonyl defect on the electrode injection characteristics of polytetrafluoroethylene film capacitor

Polymer dielectric capacitor for high energy storage is a promising energy storage technology. However, in dielectric capacitor electrode injection process may occur at the metal plate/organic polymer interface under high applied electric field, and the injected carriers will lead to the distorted electric field and the accumulation of space charge in dielectric material, which can seriously cause the breakdown of the capacitor. Furthermore, chemical defects in polymer dielectric may aggravate this effect of electrode injection. For this, based on the first principle simulation method, the effect of carbonyl defect on electrode injection properties at aluminum/polytetrafluoroethylene (PTFE) interface are studied to reveal the harm of chemical defect to dielectric capacitor insulation and to explain the potential physical mechanism. The results showed that the carbonyl defect can increase the vacuum level shift of interface and electron affinity of PTFE molecule, while decrease the ionization potential of PTFE molecule, which significantly reduce the interface charge injection barrier. Compared with the ideal interface, the electron injection barrier at the carbonyl defect interface decreased from 3.40eV to 2.29eV, and the hole injection barrier decreased from 7.39eV to 5.80eV. As a result, the injection current density of the interface with carbonyl defect is significantly higher under the same electric field.

Highly Transparent, Flexible, and Hydrophobic Polytetrafluoroethylene Thin Film Passivation for ITO/AgPdCu/ITO Multilayer Electrodes

AbstractTransparent and flexible polytetrafluoroethylene (PTFE) thin film passivation for ITO/AgPdCu (APC)/ITO (IAI) electrodes is developed to prevent severe degradation and maintain the reliable performance of the flexible IAI electrodes. Also, oxygen ion beam treatment (IBT) on the surface of the IAI electrode improves the adhesion between the top ITO and PTFE passivation layer, as well as the performance of the passivation layer. The IAI electrode with PTFE passivation exhibits constant sheet resistance, transmittance, and flexibility, even after the 85 °C and 85% RH test. However, the bare IAI electrode shows a significant increase in sheet resistance and a decrease in transmittance and flexibility, owing to the incorporation of moisture and impurities into the IAI layer, and agglomeration of the APC layer. To demonstrate the feasibility of PTFE passivation, the performance of flexible and transparent thin film heaters (TFHs) with the bare IAI and PTEF/IAI samples are compared. The better stability and reliability of the PTFE/IAI‐based TFHs than the bare IAI‐based TFHs indicate that the PTFE film effectively prevents the introduction of moisture and impurities. The performance of the TFH with PTFE/IAI electrode implies that sputtered PTFE film is a promising transparent and flexible thin film passivation for high‐quality oxide‐metal‐oxide multilayer electrodes.

O/F co-doped CNTs promoted graphite felt gas diffusion cathode for highly efficient and durable H2O2 evolution without aeration

Electrocatalytic reduction of O2 is an environmentally friendly method for H2O2 production. Design and fabrication of efficient non-metallic electrocatalytic gas diffusion cathode (GDC) with strong durability is highly desirable. Carbon nanotubes (CNTs) is a promising electrocatalytic material for 2-electron O2reduction but with unsatisfying electrocatalytic activity and stability. Hetero-atom doping of CNTs has been proved to promote its electrocatalytic selectivity for H2O2 generation, but the electrocatalytic performance of CNTs co-doped with two hetero-atoms and its synergy mechanisms need further investigation. Herein, O or F mono-doped and O/F co-doped CNTs with different O/F ratios were developed through one-step acidification and then used as the electrocatalysts on the graphite felt (GF) GDC for H2O2 generation. The electrocatalytic activity was greatly improved by the synergetic effects of O/F-containing functional groups on the surface of CNTs. The GF/CNTs-1:1 cathode with the highest contents of COOH and CFX (X ≥ 2) was found to be most efficient in H2O2electrogeneration at a wide pH range of 1–9. Further, with coating of polytetrafluoroethylene (PTFE) film, the GF/CNTs-1:1/PTFE-30 GDC exhibited extremely high activity and superior stability in 15 cycles without aeration, giving the maximum H2O2 yield of 263.2 mg·L−1in 1 h with little decline rate. The present study provides opportunities for developing highly efficient, cost effective, and durable metal-free electrocatalysts for H2O2 evolution.

A New Type of Quartz Smog Chamber: Design and Characterization.

Since the 1960s, many indoor and outdoor smog chambers have been developed worldwide. However, most of them are made of Teflon films, which have relatively high background contaminations due to the wall effect. We developed the world's first medium-size quartz chamber (10 m3), which is jointed with 32 pieces of 5 mm thick polished quartz glasses and a stainless-steel frame. Characterizations show that this chamber exhibits excellent performance in terms of relative humidity (RH) (2-80%) and temperature (15-30 ± 1 °C) control, mixing efficiency of the reactants (6-8 min), light transmittance (>90% above 290 nm), and wall loss of pollutants. The wall loss rates of the gas-phase pollutants are on the order of 10-4 min-1 at 298 K under dry conditions. It is 0.08 h-1 for 100-500 nm particles, significantly lower than those of Teflon chambers. The photolysis rate of NO2 (JNO2) is automatically adjustable to simulate the diurnal variation of solar irradiation from 0 to 0.40 min-1. The inner surface of the chamber can be repeatedly washed with deionized water, resulting in low background contaminations. Both experiments (toluene-NOx and α-pinene-ozone systems) and box model demonstrate that this new quartz chamber can provide high-quality data for investigating SOA and O3 formation in the atmosphere.

Adjustable surface activity and wetting ability of anionic hydrocarbon and nonionic short-chain fluorocarbon surfactant mixtures: Effects of Li+ and Mg2+

Achieving wide variation ranges and various adjusting modes of the performances for surfactant mixtures is still a significant challenge which limits the extensive application of surfactant mixtures. Herein, we reported the physicochemical properties and performances of hydrocarbon/fluorocarbon surfactant mixtures constituted with an anionic hydrocarbon surfactant, sodium dodecyl sulfate (SDS), and a tri-block nonionic short-chain fluorocarbon surfactant (F9EG13F9). Meanwhile, the effects of Li+ and Mg2+ on them were investigated. The surface tension and contact angle measurements were adopted to reflect the surface activity and wetting ability of SDS/F9EG13F9 mixtures. The data showed that the surface tensions at the critical micelle concentrations and the contact angles on polytetrafluoroethylene film of these surfactant mixtures are 33.5–21.4 mN/m and 118.0–58.7°, respectively, which indicates that their surface activity and wetting ability possess wide variation ranges. Furthermore, the micellization, adsorption and thermodynamics behaviors of mixed surfactants were also analyzed using a series of theoretical parameters based on the regular solution theory, Clint’s model, Maeda’s model, etc. The results approved that Li+ and Mg2+ immensely reduce the electrostatic repulsion effect of SDS and increase the adsorption of SDS at phase interfaces to enhance mixed monolayer packing, in which the effect of Mg2+ is stronger than that of Li+. Thus, precisely adjustable surface activity and wetting ability can be realized by changing the molar ratio and adding the different cations, which enables SDS/F9EG13F9 mixtures to possess tunable performances to meet various practical application requirements.

Tailoring micro/nanostructured porous polytetrafluoroethylene surfaces for dual-reversible transition of wettability and transmittance

Materials with dynamic transition are current mostly limited to two-state transition of single property. Herein, a textured polytetrafluoroethylene (PTFE) film with hierarchical porous micro/nanostructures is fabricated by one-step femtosecond laser line-by-line scanning technology. The as-prepared sample is superhydrophobic and opaque, and its wettability and optical transmittance can be simultaneously controlled. As the sample prewetted with alcohol, it displayed superhydrophilicity with high transparency. In contrast, since the prewetted surface was dried, it recovered its original superhydrophobicity and opacity. The switching repeatability, applicability of solutions, stability of the samples are also demonstrated. By using its controllable switching performances, potential applications such light pass/block controlling, anti-fogging, cooling were realized on the as-prepared surfaces. This work reports a smart surface with dual-functional transition ability, which could open fresh ideas for a broad range of multifunctional applications.

Antibacterial noncytotoxic chitosan coatings on polytetrafluoroethylene films by plasma grafting for medical device applications

Antibacterial noncytotoxic chitosan coatings on polytetrafluoroethylene films by plasma grafting for medical device applications

Investigation of deep drawing of square cups using high-strength DP600 and DP800 sheets

This study investigated the deep drawing of square cups using high-strength du-al phase DP600 and DP800 sheets via both experimental and finite element meth-ods. The limiting drawing ratio (LDR) and wall thickness distribution were exam-ined. The initial thickness of the materials used in the study was equal to 1-mm. The experiments were carried out at room temperature using both Teflon film and graphite spray lubricants at the same time. In terms of LDR, both experimental and numerical results corresponded with each other. A ratio of 1.97 LDR was reached for the DP600 steel and 1.92 LDR for the DP800. Given that the thick-ness distribution between the experimental and numerical results, an accord of over 90% was noticed. For the DP600 steel, the lowest experimental thickness value was 0.864 mm and the lowest numerical value was 0.87 mm. For the DP800 steel, the lowest experimental thickness value was measured to be 0.89 mm while the lowest numerical value was found to be 0.88 mm. In the conclusion, the pre-sent paper proves that the experimental results in the deep drawing of square cups can be achieved with very satisfying results by using numerical methods.

Surface modification of polytetrafluoroethylene film by argon cold atmospheric pressure plasmas for enhancing bonding with graphene‐filled polyimide adhesives

AbstractSignificantly enhanced adhesion of polytetrafluoroethylene (PTFE) films to graphene‐filled polyimide (PI) adhesives by argon (Ar) cold atmospheric pressure plasmas (CAPPs) at the exposure durations of 72–96 s was undertaken. Poor adhesion of PTFE film to PI adhesive with no bonding (100% delamination) was highly improved to good bonding (100% attachment) for PTFE film treated by Ar CAPPs. Hydrophobic PTFE surface (water contact angle up to 91.1°) was changed to hydrophilic PTFE surfaces (water contact angle up to 37.4°–66.0°) with Ar CAPPs treatment by formation of polar chemical bonds such as C–O and C=O. To realize how the chemical bonds of C–O and C=O were produced onto the PTFE surface by Ar CAPPs, the plasma active species of Ar CAPPs were detected by optical emission spectroscopy.

Giving Penetrable Remote-Control Ability to Thermoresponsive Fibrous Composite Actuator with Fast Response Induced by Alternative Magnetic Field.

An alternative magnetic field (AMF)-induced electrospun fibrous thermoresponsive composite actuator showing penetrable remote-control ability with fast response is shown here for the first time. The built-in heater of magnetothermal Fe3O4 nanoparticles in the actuator and the porous structure of the fibrous layer contribute to a fast actuation with a curvature of 0.4 mm−1 in 2 s. The higher loading amount of the Fe3O4 nanoparticles and higher magnetic field strength result in a faster actuation. Interestingly, the composite actuator showed a similar actuation even when it was covered by a piece of Polytetrafluoroethylene (PTFE) film, which shows a penetrable remote-control ability.