Fluoropolymer Films Research Articles

Stretchable Distributed Bragg Reflectors as Strain-Responsive Mechanochromic Sensors.

Mechanochromic materials exhibit color changes upon external mechanical stimuli, finding wide-ranging applications in colorimetric sensing, display technology, and anticounterfeiting measures. Many of these materials rely on fluorescence properties and therefore necessitate external optical or electrical excitation. However, for broader applicability, the detection of color changes by the naked eye only or without complicated detection instrumentation is highly desirable. Photonic crystals offer a promising avenue for attaining such performances. In this work, we present elastomeric distributed Bragg reflectors (DBRs) characterized by a series of photonic bandgaps exhibiting mechanochromic response from the near-infrared to the visible wavelengths. To achieve this, we engineered alternating thin films of a thermoplastic fluoropolymer and a styrene-butadiene copolymer using different elastomeric substrates to attain different behaviors. The reported system demonstrates a reversible and instantaneous shift of the photonic bandgaps in response to 100% strain in multiple deformation cycles. Comparing the DBR stress-strain response with the optical strain response confirms a mechanochromic sensitivity of ∼1.7-6.9 nm/% and ∼80 nm/MPa, with an optical Poisson's ratio in the range 0.3-0.7. All these properties are spectrally dependent, as demonstrated by exploiting the properties of different diffraction order photonic band gaps.

Homogeneity study of fluoropolymer films modified by atmospheric pressure nitrogen plasma discharges

ABSTRACT This work investigated the impact of an atmospheric pressure nitrogen plasma treatment on the surface homogeneity of a fluoropolymer film. The resulting surfaces were assessed using T-peel tests, surface energy measurements, and XPS analyses. The results showed that the treatment led to the defluorination of the fluoropolymer surface, therefore increasing its wettability. Consequently, the peel strength of the substrate drastically increased. This study also highlighted that surface energy alone is not an accurate indicator of adhesion properties. The results correlated the XPS ratio (C-O+C-N+C-C)/(CF3+CF2) with the adhesion increase.

Cryogenic Mechanical Properties and Stability of Polymer Films for Liquid Oxygen Hoses.

To select the appropriate polymer thin films for liquid oxygen composite hoses, the liquid oxygen compatibility and the cryogenic mechanical properties of four fluoropolymer films (PCTFE, ETFE, FEP and PFA) and two non-fluoropolymer films (PET and PI) before and after immersion in liquid oxygen for an extended time were investigated. The results indicated that the four fluoropolymers were compatible with liquid oxygen before and after immersion for 60 days, and the two non-fluoropolymers were not compatible with liquid oxygen. In addition, the cryogenic mechanical properties of these polymer films underwent changes with the immersion time, and the changes in the non-fluoropolymer films were more pronounced. The cryogenic mechanical properties of the two non-fluoropolymer films were always superior to those of the four fluoropolymer films during the immersion. Further analysis indicated that the fundamental reason for these changes in the cryogenic mechanical properties was the variation in the crystalline phase structure caused by the ultra-low temperature, which was not related to the strong oxidizing properties of the liquid oxygen. Analytical results can provide useful guidance on how to select the appropriate material combination to obtain a reasonable liquid oxygen composite hose structure.

Excellent-Moisture-Resistance Fluorinated Polyimide Composite Film and Self-Powered Acoustic Sensing.

As a clean, sustainable energy source, sound can carry a wealth of information and play a huge role in the Internet of Things era. In recent years, triboelectric acoustic sensors have received increasing attention due to the advantages of self-power supply and high sensitivity. However, the triboelectric charge is susceptible to ambient humidity, which reduces the reliability of the sensor and limits the application scenarios significantly. In this paper, a highly moisture-resistant fluorinated polyimide composited with an amorphous fluoropolymer film was prepared. The charge injection performance, triboelectric performance, and moisture resistance of the composite film were investigated. In addition, we developed a self-powered, highly sensitive, and moisture-resistant porous-structure acoustic sensor based on contact electrification. The detection characteristics of the acoustic sensor are also obtained.

Surface Modification Strategy for Yellow-Emitting Carbon Dots in Fluoropolymer Films

Carbon dots (CDs) were prepared from p-phenylenediamine, modified with trifluoroacetic acid, and dispersed in a fluoropolymer (FP) film. Unmodified CDs did not disperse well in the FP film, resulting in concentration quenching; whereas surface modification improved the affinity between the CDs and the FP, resulting in a homogeneous dispersion and an improved photoluminescence quantum yield.

Influence of Injection Molding Parameters on the Peel Strength between Plasma-Treated Fluoropolymer Films and Polycarbonate

Light guiding is used to direct light from an emitting source to a different location. It is frequently realized through a clad-core structure with a difference in the refractive index of the materials. This paper explores the possibility of combining a fluoropolymer (THV) film of low refractive index, serving as a cladding layer, with a polycarbonate (PC) core, via injection molding. Pristine THV lacks adherence to the PC. However, when treated with O2 plasma prior to overmolding, bonding can be established that was quantified in peel tests. The effect of this surface treatment was further investigated by adjusting the plasma treatment duration and time to overmolding. Furthermore, parameter studies comprising the four molding parameters, namely packing pressure, injection speed, melt temperature, and mold temperature, were performed. Numerical injection molding simulations assessed the prevailing temperatures at the PC-THV boundary. Consequently, the temperature-time integral could be calculated and linked with the measured peel strengths by fitting a proportionality constant. While the plasma treatment duration showed minor influence, the activation diminished with time, halving the measured peel loads within 24 h. The adhesion was experimentally found to increase with a lower packing pressure, faster injection speed, and higher melt and mold temperature. Those same molding relations influencing the peel loads were also found with the temperature-time integral when scaled by the proportionality constant in the simulations (R2=85%). Apparently, adhesion is added by molding settings which promote higher interface temperatures that prevail for longer. Hereby, the faster injection speed increases the melt temperature through shear heating. A higher packing pressure, in contrast, presumably increases the heat transfer at the PC-THV interface, accelerating the cooling. The measured peel loads were 0.3-1.6 N/mm for plasma-treated samples and nearly zero for pristine THV.

Higher Adhesion Strength Over 10 N/mm Between Rubber and Fluoropolymer Film When Treated by Atmospheric Plasma-Graft Polymerization

An evaluation of the adhesion between rubber and fluoropolymer films treated by atmospheric plasma-graft polymerization is conducted to realize a low-permeation fuel rubber hose covered with fluoropolymer. The low-permeation fuel rubber hose is important for reducing vehicular evaporative emissions. Although fluoropolymers have extremely low permeability for fuel, it is difficult to bond them with other materials, such as rubber, because of their low adhesive properties. Plasma surface modification has been investigated to improve the adhesive properties of fluoropolymers. However, it is difficult to realize effective and permanent surface treatment using plasma alone. Based on the new and effective combined plasma surface-modification technique for fluoropolymer films, we previously proposed an atmospheric-pressure plasma method followed by graft polymerization of hydrophilic monomers such as acrylic acid (CH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> = CHCOOH). In this study, three types of rubber, isobutylene isoprene rubber (IIR), ethylene acrylic elastomer (AEM), as well as white-colored ethylene acrylic elastomer (white AEM), and two types of fluoropolymer films, denatured PFA-1 and denatured PFA-2, were prepared. The treated fluoropolymer film and rubber were adhered using vulcanized adhesion, and then the 180° peeling strength test was conducted. The results show that an average peeling strength of 12.6 N/mm and a maximum peeling strength of 15.3 N/mm, which are over 10 N/mm, are attained for the sample of vulcanized bonding of the treated denatured PFA-1 and AEM.

Organic thin-film transistors with inkjet-printed electrodes on hydrophobic Teflon-AF gate dielectric with reversible surface properties

Printed organic thin-film transistors (OTFTs) are promising for flexible, low-cost electronics; however, a major challenge is that successive processing steps of multiple solution-processed layers can interfere with each other. In particular, hydrophobic fluoropolymers are a promising group of materials to fabricate gate dielectrics with low charge trap density and properties such as good thermal stability, chemical inertness, low dielectric constant, and water repellency. However, the main difficulty in incorporating hydrophobic fluoropolymers in printed electronic devices is their low surface energy. Plasma treatment is a common method for surface modification that renders these hydrophobic layers wettable to print subsequent layers. This plasma processing can also affect the interface with the organic semiconductor (OSC) and transistor performance, which is studied here for the first time. The morphological and surface chemical properties of Teflon amorphous fluoropolymer (Teflon-AF) films change after plasma treatment and gradually reverse after post-annealing of subsequent layers as demonstrated here. Here, we fabricate solution-processed OTFTs with Teflon-AF as the gate dielectric. We report OTFTs with inkjet-printed source and drain electrodes with a minimum channel length of 20 μm on Teflon-AF for the first time. We show that the annealing of the inkjet-printed electrodes changes the morphology and the surface chemistry of the Teflon-AF gate dielectric underneath, thus reversing the effect of the plasma. We show that this electrode post-annealing step can improve the transistor performance by improving the interface between the Teflon-AF gate dielectric and the OSC in terms of smoothness and hydrophobicity. The transistor parameters such as mobility, on/off current ratio, and threshold voltage all follow a trend explained here by the properties of the Teflon-AF films. Increasing the post-annealing temperature to just below complete surface reversibility decreases surface roughness and trap-sites created after plasma treatment leading to optimized device performance. We characterize the Teflon-AF surface with contact angle measurement, roughness measurement, Fourier transform infrared spectroscopy (FTIR), and x-ray photoelectron spectroscopy (XPS). This understanding of the reversibility of the Teflon-AF surface helps achieve optimal performance of devices and systems incorporating fluoropolymers. • The challenge of processing OTFT layers on hydrophobic dielectrics is addressed. • 20 μm channel OTFTs with inkjet-printed electrodes on hydrophobic dielectric are achieved. • Teflon-AF surface changes after plasma and reverses after post-annealing. • Electrode annealing changes the morphology and surface chemistry of the dielectric. • Electrode annealing can improve the gate dielectric/organic semiconductor interface.

Dielectric breakdown driven by flexoelectric and piezoelectric charge generation as hotspot ignition mechanism in aluminized fluoropolymer films

Using multiphysics simulations and experiments, we demonstrate that dielectric breakdown due to electric charge accumulation can lead to sufficient hotspot development leading to the initiation of chemical reactions in P(VDF-TrFE)/nAl films comprising a poly(vinylidene fluoride-co-trifluoroethylene) binder and nano-aluminum particles. The electric field (E-field) development in the material is driven by the flexoelectric and piezoelectric responses of the polymer binder to mechanical loading. A two-step sequential multi-timescale and multi-physics framework for explicit microscale computational simulations of experiments is developed and used. First, the mechanically driven E-field development is analyzed using a fully coupled mechanical–electrostatic model over the microsecond timescale. Subsequently, the transient dielectric breakdown process is analyzed using a thermal–electrodynamic model over the nanosecond timescale. The temperature field resulting from the breakdown is analyzed to establish the hotspot conditions for the onset of self-sustained chemical reactions. The results demonstrate that temperatures well above the ignition temperatures can be generated. Both experiments and analyses show that flexoelectricity plays a primary role and piezoelectricity plays a secondary role. In particular, the time to ignition and the time to pre-ignition reactions of poled films (possessing both piezoelectricity and flexoelectricity) are ∼10% shorter than those of unpoled films (possessing only flexoelectricity).

SmartPrint Single-Mode Flexible Polymer Optical Interconnect for High Density Integrated Photonics

This paper reports on the demonstration of a single-mode flexible polymer optical interconnect for efficiently and conveniently connecting integrated photonics chips to one another (chip-to-chip) and to optical printed circuit boards (chip-to-board). The interconnect uses a low-loss partially fluorinated refractive index contrast (RIC) polymer, referred to as poly(F-SBOC), that provides for direct patterning of the desired refractive index profiles into a slab waveguide consisting of poly(F-SBOC) and a flexible fluoropolymer film (Tefzel). Using a maskless lithography system, interconnects consisting of s-bends and tapers can be printed in situ into the poly(F-SBOC) material with no need for mechanical alignment. We demonstrate the efficacy of this approach by connecting two separate ion-exchange (IOX) glass waveguide chips, achieving fiber-to-fiber total insertion losses below 6dB in some cases, through the use of grayscale tapers that are written directly into the poly(F-SBOC) material.

Selectively emissive fluoropolymer film for passive daytime radiative cooling

Passive daytime radiative cooling is an attractive method to reduce overheating and the heat island effect, thus addressing the global warming effect. This technology does not require any input energy, noise, vibrations, and polluting gas to produce sub-ambient temperatures. In this study, we propose a simple passive daytime radiative cooler, composed of a silver back layer and commercial ethylene tetrafluoroethylene film. With many molecular vibration peaks in the sky window and high solar transmittance of ethylene tetrafluoroethylene, the silver-deposited film exhibits only 3.5% solar absorption and 88.6% emissivity in the sky window, resulting in a substantial sub-ambient cooling effect of up to 9.7 °C in outdoor measurements. The theoretical prediction was confirmed to match well with experimental results, and the passive daytime radiative cooling ability of the film was examined using global-scale cooling energy density maps.

Biomimetic Porous Fluoropolymer Films with Brilliant Whiteness by Using Polymerization‐Induced Phase Separation (Adv. Mater. Interfaces 1/2022)

Biomimetic Porous Fluoropolymer Films In article number 2101485, Binhai Yu, Shudong Yu, and co-workers prepare biomimetic porous fluoropolymer films with brilliant whiteness by using polymerization-induced phase separation method. With a well-tailored pore morphology, the as-prepared porous fluoropolymer films feature a comparable scattering ability to the benchmark Cyphochilus scale. With such remarkable scattering performance, the porous fluoropolymer films can find many applications, such as optoelectronic devices and daytime passive radiative cooling.

Disposition of Fluorine on New Firefighter Turnout Gear.

Firefighter turnout gear is essential for reducing occupational exposure to hazardous chemicals during training and fire events. Per-and polyfluoroalkyl substances (PFASs) are observed in firefighter serum, and possible occupational sources include the air and dust of fires, aqueous film-forming foam, and turnout gear. Limited data exist for nonvolatile and volatile PFASs on firefighter turnout gear and the disposition of fluorine on the individual layers of turnout gear. Further implications for exposure to fluorine on turnout gear are not well understood. Three unused turnout garments purchased in 2019 and one purchased in 2008, were analyzed for 50 nonvolatile and 15 volatile PFASs by liquid chromatography quadrupole time-of-flight mass spectrometry (LC-qTOF-MS) and gas chromatography-mass spectrometry (GC-MS), respectively. Particle-induced gamma ray emission (PIGE), a surface technique, and instrumental neutron activation analysis (INAA), a bulk technique, were used to measure total fluorine. Bulk characterization of the layers by pyrolysis-GC/MS (py-GC/MS) was used to differentiate fluoropolymer (e.g., PTFE) films from textile layers finished with side-chain polymers. The outer layer, moisture barrier, and thermal layers of the turnout gear all yielded measured concentrations of volatile PFASs that exceeded nonvolatile PFAS concentrations, but the summed molar concentrations made up only a small fraction of total fluorine (0.0016-6.7%). Moisture barrier layers comprised a PTFE film, as determined by py-GC-MS, and gave the highest individual nonvolatile (0.159 mg F/kg) and volatile PFAS (20.7 mg F/kg) as well as total fluorine (122,000 mg F/kg) concentrations. Outer and thermal layers comprised aromatic polyamide-based fibers (aramid) treated with side-chain fluoropolymers and had lower levels of individual nonvolatile and volatile PFASs. Equal concentrations of total fluorine by both PIGE and INAA on the outer and thermal layers is consistent with treatment with a side-chain fluoropolymer coating. New turnout gear should be examined as a potential source of firefighter occupational exposure to nonvolatile and volatile PFASs in future assessments.

Passivation of miniature microwave coplanar waveguides using a thin film fluoropolymer electret

The insertion losses of miniature gold/silicon-on-insulator (SOI) coplanar waveguides (CPW) are rendered low, stable, and light insensitive when covered with a thin film (95 nm) fluoropolymer deposited by a trifluoromethane (CHF3) plasma. Microwave characterization (0–50 GHz) of the CPWs indicates that the fluoropolymer stabilizes a hydrogen-passivated silicon surface between the CPW tracks. The hydrophobic nature of the fluoropolymer acts as a humidity barrier, meaning that the underlying intertrack silicon surfaces do not re-oxidize over time—something that is known to increase losses. In addition, the fluoropolymer thin film also renders the CPW insertion losses insensitive to illumination with white light (2400 lx)—something potentially advantageous when using optical microscopy observations during microwave measurements. Capacitance–voltage (CV) measurements of gold/fluoropolymer/silicon metal–insulator-semiconductor (MIS) capacitors indicate that the fluoropolymer is an electret—storing positive charge. The experimental results suggest that the stored positive charge in the fluoropolymer electret and charge trapping influence surface-associated losses in CPW—MIS device modelling supports this. Finally, and on a practical note, the thin fluoropolymer film is easily pierced by commercial microwave probes and does not adhere to them—facilitating the repeatable and reproducible characterization of microwave electronic circuitry passivated by thin fluoropolymer.

Fluoropolymer-based organic memristor with multifunctionality for flexible neural network system

In this study, we propose an effective strategy for achieving the flexible one organic transistor–one organic memristor (1T–1R) synapse using the multifunctional organic memristor. The dynamics of the conductive nanofilament (CF) in a hydrophobic fluoropolymer medium is explored and a hydrophobic fluoropolymer-based organic memristor is developed. The flexible 1T–1R synapse can be fabricated using the solution process because the hydrophobic fluorinated polymer layer is produced on the organic transistor without degradation of the underlying semiconductor. The developed flexible synapse exhibits multilevel conductance with high reliability and stability because of the fluoropolymer film, which acts as a medium for CF growth and an encapsulating layer for the organic transistor. Moreover, the synapse cell shows potential for high-density memory systems and practical neural networks. This effective concept for developing practical flexible neural networks would be a basic platform to realize the smart wearable electronics.

Biomimetic Porous Fluoropolymer Films with Brilliant Whiteness by Using Polymerization‐Induced Phase Separation

AbstractInspired by the Cyphochilus scale with extreme whiteness, fluoropolymer is used as the matrix to prepare highly scattering porous polymer films through polymerization‐induced phase separation (PIPS) method. The mixture used for the PIPS technique contains a fluoride monomer, a UV photoinitiator, and porogens (cyclohexanol and perfluorooctanol). By carefully tuning the mixture parameters (cyclohexanol–perfluorooctanol and monomer–porogen weight ratios), the porous morphology can be well tailored, which induces different scattering performances. With an optimized formulation (50 wt% monomer, 25 wt% cyclohexanol, and 25 wt% perfluorooctanol), the porous film with a thickness of 55 µm can achieve an average total reflectance of ≈90%, featuring a measured transport mean free path of 1.3–1.7 µm (comparable to the 1.5 µm of the benchmark Cyphochilus scale). Further, the porous films are applied to the light‐emitting diode (LED) device and it is demonstrated that they can effectively improve the light extraction efficiency of the LED and thus enhance the luminous performance. Due to the simplicity, cost‐effectiveness, and scalability of the PIPS method, the as‐developed porous fluoropolymer films with such excellent scattering ability can find many potential applications not only in the field of optoelectronics, but also in various complex scenarios, such as daytime passive radiative cooling.

Plasma-induced Surface Modification of Fluoropolymer Films for Direct Adhesion with Copper

Plasma-induced Surface Modification of Fluoropolymer Films for Direct Adhesion with Copper

Fluoropolymer Film Formation by Electron Activated Vacuum Deposition

Polytetrafluoroethylene (PTFE), polyhexafluoropropylene (PHFP) and polychlorotrifluoroethylene (PCTFE) were heated to their decomposition temperature in a high vacuum. The emitted fragments passed an electron cloud, condensed on a substrate and formed fluoropolymer film. Growth rate of PTFE and PHFP films increased up to a factor five in the presence of the electron cloud. Mass spectrometry revealed changes in the mass spectra of fragments generated by thermal decomposition only and formed under electron activation. The observed changes were different for each fluoropolymer. Infrared spectroscopy (IRS) showed that the structure of the films was close to the structure of the bulk polymers. Atomic force microscopy (AFM) has revealed different morphologies of PTFE, PHFP and PCTFE films, suggesting a Volmer–Weber growth mechanism for PTFE and PHFP but a Frank-van der Merwe one for PCTFE. All films were smooth at nanoscale and transparent from ultraviolet to near-infrared region. Additional radio frequency (RF) plasma ignited in the emitted fragments at a low pressure increased mechanical characteristics of the films without losing their optical transparency and smoothness.

CFD modeling of pharmaceuticals and CECs removal by UV/H2O2 process in helical microcapillary photoreactors and evaluation of OH radical rate constants

Process intensification by tailored secondary flow in helical microcapillary film (MCF) photoreactors was unveiled by computational fluid dynamics, and it was revealed for the removal of six common contaminants of emerging concern CECs (the antiviral Acyclovir, the antiretrovirals Stavudine and Zidovudine, and the biocidal antifungal agents Methylisothiazolinone, Benzisothiazolinone and Isoxazole) in water by UV hydrogen peroxide. The MCF photoreactors consisted of fluoropolymer films containing 10 microchannels with diameter varying from 100 to 1000 µm coiled around a UVC lamp. In contrast to a MCF with straight channels, mixing intensification by secondary flow (Dean vortices) caused by the helical shape of the microcapillary strongly enhanced the radial fluid mixing, further supplementing the transport of the reacting species by Taylor-Aris dispersion. The intensity of the Dean vortices formed was correlated to the Dean (De) and Schmidt (Sc) numbers through a new correlation for the radial Peclet, which established that these become significant when De1.94Sc>67. Thus, the second-order reaction rate constant of the six CECs with OH• radicals (kOH) determined in a helical MCF photoreactor increased (4.4% up to 37.9%) in comparison to those determined assuming a MCF photoreactor with plug flow. In addition, the helical shape of the MCF significantly diminished mass transfer limitations and decreased the CECs Electrical Energy per Order Reduction (EEO), paving the way for scaling-up of helical microcapillary photoreactor technology. This study shows how micromixing can be successfully exploited to design more efficient microcapillary photoreactors.

Hot-Wire Chemical Vapor Deposition of Fluoropolymer Coatings on Rotating Cylindrical Surfaces

The method of hot-wire activated chemical vapor deposition (HW CVD) of fluoropolymer films has been adapted to obtain fluoropolymer coatings on rotating cylindrical surfaces of small radius (below 20 mm). The influence of the substrate rotation speed on the structure of thin fluoropolymer deposit was studied and revealed significant dependence of the coating morphology on the speed of cylindrical surface rotation, which is an additional parameter that can be used to control the structure of fluoropolymer coating during the HW CVD process.