Polytetrafluoroethylene Polymer Research Articles

Enhanced performance and stability of high temperature proton exchange membrane fuel cell by incorporating zirconium hydrogen phosphate in catalyst layer

Zirconium hydrogen phosphate (ZHP) together with polytetrafluoroethylene (PTFE) polymer binder is incorporated into the catalyst layers (CLs) of ABPBI (poly(2,5-benzimidazole))-based high temperature polymer electrolyte membrane fuel cell (HT-PEMFCs) to improve its performance and durability. The influence of ZHP content (normalised with respect to dry PTFE) on the CL properties are structurally characterised by scanning electron microscopy (SEM) and mercury intrusion porosimetry. Electrochemical analyses of the resultant membrane electrode assemblies (MEAs) are performed by recording polarisation curves and impedance spectra at 160 °C, ambient pressure and humidity. The result show that a 30 wt.% ZHP/PTFE content in the CL is optimum for improving fuel cell performance, the resultant MEA delivers a peak power of 592 mW cm−2 at a cell voltage of 380 mV. Electrochemical impedance spectra (EIS) indicate that 30% ZHP in the CL can increase the proton conductivity compared to the pristine PTFE-gas diffusion electrode (GDE). A short term stability test (∼500 h) on the 30 wt.% ZHP/PTFE-GDE shows a remarkable high durability with a degradation rate as low as ∼19 μV h−1 at 0.2 A cm−2, while 195 μV h−1 was obtained for the pristine GDE.

Phase transition modeling of polytetrafluoroethylene during Taylor impact

The complex pressure and temperature dependent phase behavior of the semicrystalline polymer polytetrafluoroethylene (PTFE) has been investigated experimentally. One manifestation of this behavior has been observed as an anomalous abrupt ductile-to-brittle transition in the failure mode of PTFE rods in Taylor cylinder impact tests when impact velocity exceeds a narrow critical threshold. Earlier, hydrocode calculations and Hugoniot estimates have indicated that this critical velocity corresponds to the pressure in PTFE associated with the transition from a crystalline phase of helical structure to the high pressure crystalline phase (phase III) of a planar form. The present work represents PTFE as a material in a simplified phase structure with the transition between the modeled phases regulated by a kinetic description. The constitutive modeling describes the evolution of mechanical characteristics corresponding to the change of mechanical properties due to either an increase of crystallinity or the phase transition of a crystalline low-pressure component into phase III. The modeling results demonstrate that a change in the kinetics of the transition mechanism in PTFE when traversing the critical impact velocity can be used to explain the failure of the polymer in the Taylor cylinder impact tests.

The Fourier space restricted Hartree-Fock method for the electronic structure calculation of linear poly(tetrafluoroethylene)

Building on the pioneering work of Jean-Marie Andre and working in the laboratory he founded, the authors have developed a code called FT-1D to make Hartree-Fock electronic structure computations for stereoregular polymers using Ewald-type convergence acceleration methods. That code also takes full advantage of all line-group symmetries to calculate only the minimal set of two-electron integrals and to optimize the computation of the Fock matrix. The present communication reports a benchmark study of the FT-1D code using polytetrafluoroethylene (PTFE) as a test case. Our results not only confirm the algorithmic correctness of the code through agreement with other studies where they are applicable, but also show that the use of convergence acceleration enables accurate results to be obtained in situations where other widely-used codes (e.g., PLH and Crystal) fail. It is also found that full attention to the line-group symmetry of the PTFE polymer leads to an increase of between one and two orders of magnitude in the speed of computation. The new code can therefore be viewed as extending the range of electronic-structure computations for stereoregular polymers beyond the present scope of the successful and valuable code Crystal.

Chemical Reaction Mechanism of Polytetrafluoroethylene on Aluminum Surface under Friction Condition

To develop a novel shearing resin material, it is necessary to understand the mechanism of friction-induced chemistry during the friction process. For this purpose, the chemical reaction of the polytetrafluoroethylene (PTFE) resin on an aluminum surface during friction was first focused on and investigated by a quantum chemical molecular dynamics method. From our simulation, an aluminum atom on a native oxide of aluminum surface led to a tribochemical reaction, which included defluorination of PTFE and aluminum fluoride formation. It was inferred that the aluminum surface acted as a catalytic Lewis acid in which the fluorine atom was removed from the PTFE polymer chain. The tribological performance of the investigated system was reduced by the forming of aluminum fluoride since a self-lubrication by PTFE was inhibited by an interfacial electrostatic repulsion. On the basis of our study, it was suggested that the key to increase tribological performance was a chemical reaction between reactive defluorinate...

Effect of Polytetrafluoroethylene additive on low-temperature synthesis of InN crystals via reaction of LiInO<sub>2</sub> and NaNH<sub>2</sub>

We examined the effect of polymer polytetrafluoroethylene (PTFE) additive on the growth of InN crystals by the nitridation of LiInO2 in NaNH2 flux at 240°C. LiInO2 and NaNH2 powder were heated with/without PTFE pieces in a steel crucible located inside the PTFE-lined autoclave. The additive of PTFE pieces enhanced the decomposition of LiInO2 with the mass loss of these pieces and progressed the formation of InN and In(OH)3 byproducts. SEM and TEM images of the products using PTFE additives showed the hexagonal InN crystals of ~1 µm in size, and the optical bandgap of synthesized InN was estimated as ~2.03 eV. We presume that fluorine in PTFE additive subtracts Li from LiInO2 and enhances the growth of InN crystals.

Progress toward understanding the bioaccumulation of perfluorinated alkyl acids

Progress toward understanding the bioaccumulation of perfluorinated alkyl acids

An in vitro study assessing the effect of mesh morphology and suture fixation on bacterial adherence

Prosthetic infections, although relatively uncommon in hernia surgery, are a source of considerable morbidity and cost. The aims of this experimental study were to assess the influence of the morphological properties of the mesh on bacterial adherence in vitro. The morphological properties assessed were the polymer type, filament type, filament diameter, mesh weight, mean pore size, and the addition of silver chlorhexidine and titanium coatings. In addition, the study assessed the effect on bacterial adherence of adding a commonly used suture to the mesh and compared adherence rates to self-gripping mesh that does not require suture fixation. Eight commercially sourced flat hernia meshes with different material characteristics were included in the study. These were Prolene(®) (Ethicon(®)), DualMesh(®) (Gore(®)), DualMesh(®) Plus (Gore(®)), Parietex™ ProGrip (Covidien™), TiMesh(®) Light (GfE Medical), Bard(®) Soft Mesh (Bard(®)), Vypro(®) (Ethicon(®)), and Omyra(®) (Braun(®)). Individual meshes were inoculated with Staphylococcus epidermidis and Staphylococcus aureus with a bacterial inoculum of 10(2) bacteria. To assess the effect of suture material on bacterial adhesion, a sterile piece of commonly used monofilament suture material (2.0 Prolene(®), ZB370 Ethicon(®)) was sutured to selected meshes (chosen to represent different commonly used polymers and/or the presence of an antibacterial coating). Inoculated meshes were incubated for 18 h in tryptone soy broth and then analysed using scanning electron microscopy. A previously validated method for enumeration of bacteria using automated stage movement electron microscopy was used for direct bacterial counting. The final fraction of the bacteria adherent to the mesh was compared between the meshes and for each morphological variable. One-way analysis of variance (ANOVA) was performed on the bacterial counts. Tukey's test was used to determine the difference between the different biomaterials in the event the ANOVA was significant. Properties that significantly increased the mean bacterial adherence were the expanded polytetrafluoroethylene polymer (P < 0.001); multifilament meshes (P < 0.001); increased filament diameter (P < 0.001); increased mesh weight (P < 0.001); and smaller mean pore size (P < 0.001). In contrast, mesh coating with antibacterial silver chlorhexidine significantly reduced bacterial adhesion (S. epidermidis mean bacterial count 140.7 ± 19.1 SE with DualMesh(®) vs. 2.3 ± 1.2 SE with DualMesh(®) Plus, P < 0.001; S. aureus mean bacterial count 371.7 ± 22.7 SE with DualMesh(®) vs. 19.3 ± 4.7 SE with DualMesh(®) Plus, P = 0.002). The addition of 2.0 Prolene suture material significantly increased the mean number of adherent bacteria independent of the mesh polymer or mesh coating (P = 0.04 to <0.001). The present study demonstrates the significant influence of the prosthetic load on bacterial adherence. In patients at increased risk of infection, low prosthetic load materials, i.e., lightweight meshes with large pores, may be beneficial. Furthermore self-fixing meshes, which avoid increasing the prosthetic load and antibacterial impregnated meshes, may have an advantage in this setting.

Nanoceramic and Polytetrafluoroethylene Polymer Composites for Mechanical Seal Application at Low Temperature

We investigated the tribochemical and wear properties of Polytetrafluoroethylene (PTFE) based polymer matrix composites with nanoceramic (NC) -sialon, and particles for the mechanical seal applications at low temperature. SEM showed that NC particles were homogeneously distributed in the polymer matrix and initiated the formation of the supramolecular spherulites around NC. From the temperature stimulated depolarization (TSD) current results, it was analyzed that the surface charge on nanoceramic affected the formation of the spherulites structure. 2 wt % NC did not degrade the mechanical properties of PTFE so that composites showed the similar values of tensile strength, elongation at the rupture and friction coefficient as those of neat PTFE. However, the composite with 2 wt % NC revealed the improved wear resistance, wear rate of 0.4-1.2 mg/h at room temperature and 0.28 mg/h at , respectively, while the neat PTFE the 70-75 mg/h at room temperature and 70.3 mg/h at .

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.

Ballistic energy transport via perfluoroalkane linkers

Intramolecular energy transport in a series of perfluoroalkane oligomers with various chain lengths of 3, 5, 7, 9, and 11 carbon atoms terminated by a carboxylic acid moiety on one end and –CF2H group on another end is studied by relaxation-assisted two-dimensional infrared spectroscopy. Perfluoroalkane oligomers adopt an extended structure with antiperiplanar orientation of the neighboring carbon atoms. The energy transport initiated by exciting the CO stretching mode of the acid was recorded by measuring a cross-peak amplitude between the CO stretch and the C–H bending mode as a function of the waiting time between the excitation and probing. A linear dependence of energy transport time vs. chain length is found, which suggests a ballistic energy transport mechanism. The energy transport speed, measured from the chain-length dependence of the half-rise time, T½, was found to be ca. 1150m/s, which is close to the longitudinal speed of sound in Teflon polymers.

Nanocomposite Teflon AF 2400 Films as Tunable Platforms for Selective Transport

The performance of polymeric film-based sensors, separations, including extractions, depends on solute transport rates and selectivity. The membrane's chemical composition, its state (e.g, crystalline, glassy, rubbery), and its fractional free volume are all important in defining performance attributes. Other properties of films important in sensors are robustness in the environment, chemical inertness and biocompatibility, thermal stability, and optical transparency. With the long-term goal of selective transport/extraction based on molecular recognition, we have focused on fluorous media such as Teflon AF 2400. We present a novel approach to create nanocomposite Teflon AF 2400 films with the polymer in different states to facilitate permeation and fluorous selectivity in liquid phase transport. Films cast from stable suspensions of the fluorocarbon polymer Teflon AF 2400 (T(g) ∼ 240 °C), fluoroalkylsilane-modified solid, low polydispersity silica nanoparticles (FNPs: 116 nm diameter), and with or without a plasticizer (perfluorotripentylamine, FC-70) are macroscopically homogeneous. The nanocomposite films with glassy polymer absorb considerable solvent, CHCl(3), when in contact with solutions. Thus, the films are very permeable to solutes (toluene and octafluorotoluene) from CHCl(3) solution with poor selectivity for the fluorinated solute. Plasticized Teflon AF nanocomposite films show very low solvent sorption, improved fluorocarbon/hydrocarbon selectivity, and excellent transport rates. This is an unprecedented example demonstrating the effect of a plasticizer to create polymer nanocomposites with different chemical and barrier properties. The state of the polymer in the nanocomposites dictates chemical properties. The chemical properties dictate the transport behavior. In all cases, the films are dimensionally and thermally quite stable, making them ideal materials for applications in separations and sensors.

Tuning of the ion release properties of silver nanoparticles buried under a hydrophobic polymer barrier

Tuning of Ag ion release from silver-polymer nanocomposites is very important for biomedical applications of nanocomposite materials to reduce the potential toxicity effects toward human cells. In this work a well defined model system consisting of nearly two dimensional silver nanoparticle arrangements which are either directly accessible or covered by polymer barrier was used. The Ag nanoparticles (AgNPs) with nominal thickness ranging from 1.3 to 8.3 nm and the polytetrafluoroethylene polymer layers were synthesized by physical vapor deposition techniques. Study of the Ag ion release was accompanied with a control of the composite morphology (Ag nanoparticle size, concentration, and distribution) to understand the mechanism and the kinetics of the interfacial ion transfer reactions of the AgNPs. The surface plasmon resonance of the AgNPs and the composite morphology variation as well as the time-dependent release of silver ions after immersion in water were examined by UV-visible spectroscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and inductively coupled plasma mass spectrometry. A correlation between changes in the surface plasmon resonance, composite morphology, and the kinetics of Ag ion release was found. It is shown that the strong dependence of the silver ion release on the particles' size leads to significant redistribution of the composite morphology and suppression of the Ag ? release with time. It is also observed that a polymer barrier stabilizes the morphology of the composites and can be applied to control the Ag ion release rate.

J044116 医療用異種高分子材料とPTFEの接着

The effects of hot-press after homogeneous low voltage electron beam irradiation (HLEB1) on the adhesive force (^oF_p) of peeling resistance of laminated sheets of polytetrafluoroethylene (PTFE) and different polymers of polypropylene (PP) and polyethylene (PE) were investigated without glue. The adhesion with large ^oF_p between PTFE and different polymers of PE and PP treated by HLEBI was observed, although ^oF_p of the sample without HLEBI was negligible small within the experimental error. In order to discuss the influence of DST on °FP, electron spin resonance (ESR) signals related to dangling bonds were observed. When HLEBI cut the chemical bonds and generated dangling bonds with nonbonding electrons at terminated atoms in monomers of PTFE, PP and PE, the nonbonding electrons induced not only the intermolecular attractive force but also chemical bonding. Therefore, the hot- pressing after HLEBI was a useful tool for quick lamination of PTFE and different polymers of PP and PE without glue.

Investigation of Surface Free Energy for PTFE Polymer by Bipolar Argon Plasma Treatment

The low ion energy argon plasma was used for surface modification of Poly tetra fluoroethylene (PTFE) polymer. The plasma was generated between two plane metal electrode by using 50 kHz bipolar power supply. The plasma treated surface was characterized by atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The surface free energy (SFE) of plasma treated surface was calculated from contact angle measurement. SFE increases from 33.39 mJ/m2 to 41.40 mJ/m2 with the increase in plasma treatment time and the corresponding contact angle changed from 76? to 60?. XPS study shows that F/C ratio change from 1.8 (untreated) to 1.3 (treated) and O/C ratio changes from 0.094 (untreated) to 0.148 (treated). The XPS analysis shows that both F1s and the C1s spectra for PTFE are marginally modified by plasma treatment. AFM study shows that the average surface roughness (Ra) increased from 8.5 nm to 22.8 nm after plasma treatment. Vicker’s micro hardness of the film increases upon plasma treatment. The increase in SFE after plasma treatment is attributed to the functionalization of the polymer surface with hydrophilic groups as supported from the above observations.

Superconductivity in WO2.6F0.4synthesized by reaction of WO3with teflon

WO3-xFx (x < 0.45) perovskite-like oxyfluorides were prepared by a chemically reducing fluorination route using the polymer polytetrafluoroethylene (Teflon). The symmetry of the crystal structures of WO3-xFx changes from monoclinic to tetragonal to cubic as the fluorine content increases. Fluorine doping changes insulating WO3 to a metallic conductor, and superconductivity (Tc = 0.4 K) was discovered in the samples with fluorine contents of 0.41 < x < 0.45. This easy fluorination method may be applicable to other systems and presents an opportunity for finding new oxyfluoride superconductors.

A fluorinated polymer/inorganic composite electrolyte membrane for intermediate temperature fuel cells

SUMMARY Composite membranes based on polytetrafluoroethylene (PTFE) and silicon dioxide (PTFE/SiO2 × HPO3) are fabricated to act as a fuel cell membrane for operation at temperatures from 120 to 200°C. A porous PTFE membrane is used as the membrane supporting structure and SiO2 × HPO3 sol as the proton conductor. SEM and EDX show that the sol clusters are connected together and adhered to the PTFE polymer. This structure completely fills the pores of the PTFE and minimises the gas cross-over. The PTFE/SiO2 × HPO3 membrane has a high proton conductivity, up to 0.14 S cm−1 at a relative humidity lower than 0.5%. The PTFE/SiO2 × HPO3 composite membrane gives the modest performance when it is tested in a hydrogen fuel cell although it is a potential material for the intermediate-temperature proton-conducting membrane fuel cell. Copyright © 2011 John Wiley & Sons, Ltd.

Multilevel character of deformation of polymers

The inhomogeneity in the creep rate of polymers on different scales of deformation has been studied by laser interferometry. The main results have been obtained for the amorphous-crystalline polymer polytetrafluoroethylene. The deformation characteristics are the oscillation periods of the rate (jumps of deformation), oscillation amplitudes of the rate, and the scatter of these quantities. Application of computer methods for processing of the results has made it possible to determine the difference and similarity between jumpwise deformations on different structural levels, including the nanolevel. For a more distinct separation of deformation levels, the measurements have been made in a magnetic field and outside the magnetic field. Deformation jumps have been found on five levels: from 4 nm to more than 10 μm. Introduction of a sample into a magnetic field changes the characteristics of jumps; in this case, the scatter in the values of jumps always increases, whereas their average value varies differently on different scale levels. The measurement of the parameters of deformation jumps on different scales allows one to study the laws of the development of the deformation process and the evolution of structural inhomogeneities.

Mechanical characterization of polytetrafluoroethylene polymer using full-field displacement method

The aim of this work is to estimate two important material properties of the polytetrafluoroethylene (PTFE) polymer by means of a single experimental test. The displacement fields around a crack tip are used for estimating the modulus of elasticity (or, Young's modulus) and Poisson's ratio. These parameters are evaluated by fitting linear fracture mechanic expression of displacement fields in the vicinity of the crack, for mode I, to the experimental data. Measurements of these displacements are carried out using digital image correlation (DIC) method. In this way, the experimental procedure is conducted by loading a double-edge-cracked plate specimen. In order to validate the results, two available experimental tests have been performed. The modulus of elasticity is determined by means of the tensile test, using a standard test machine. Moreover, the Poisson's ratio is obtained by measuring lateral compressive and longitudinal extensional strain using DIC method.

Osteogenic Potential of Mesenchymal Stem Cells on Expanded Polytetrafluoroethylene Coated with Both a Poly-Amino-Acid Urethane Copolymer and Collagen

We have developed an expanded polytetrafluoroethylene polymer (e-P) coated with both poly-amino-acid urethane copolymer and collagen (e-PPC) to be used for cell culture substrata. Rat mesenchymal stem cells (MSC) were cultured on the e-P and e-PPC polymers in the presence of dexamethasone. After 24 h, the MSC contacted well with the e-PPC surface and after 14 days, the MSC showed high levels of alkaline phosphatase activity, and calcium and bone-specific osteocalcin protein deposition. The MSC cultured on these polymers for 1 week were then implanted at rat subcutaneous sites and harvested after 4 weeks. Microcomputed tomography as well as histological analyses showed that any hard tissue could not be seen in implants of the MSC/e-P composites, whereas new bone formation could be detected in the MSC/e-PPC composites. These in vitro as well as in vivo results confirmed the importance of polymer surface to support the osteogenic differentiation, which resulted in new bone formation. The surface modification using poly-amino-acid urethane copolymer and collagen together with tissue engineering technology might facilitate bone anchoring to the polymers for dental and orthopedic applications.

Nanosecond S-type Electrical Instability in Carbon-Nanotube–Polymer Composites

Composites materials comprising carbon nanotubes (CNTs) embedded in a teflon polymer matrix are synthesized. The diameter and length of the CNTs are 8–10 nm and up to 150 nm, respectively. The SEM technique is used to characterize the morphology of the composites. The electrical properties are studied by recording the I–V characteristics in the nanosecond pulse mode of measurements. The typical I–V curves exhibit an S-type instability. Close to the critical voltage U c , the I–V curves are typical of multi-walled CNTs; above U c , the ohmic I–V behavior resulting from the thermally induced destruction of CNTs is observed. The statistical distribution of the resistance over the sample area is established. The experimentally observed effects are attributed to multi-walled CNTs.