Bulk Polytetrafluoroethylene Research Articles

Measurement of stiffness and damping constant of self-assembled monolayers

We design and fabricate an apparatus which uses two dual double cantilever flexures to probe mechanical properties of self-assembled monolayers (SAM) under compression. The cantilevers were designed to give stiffness of the same order as the SAM. One of the cantilevers carrying the probe is vibrated sinusoidally at subresonance frequency and subnanometric amplitude while the dynamic response of the other carrying the SAM is recorded in the contact mode to yield data which could be deconvoluted to give stiffness and damping constant of the SAM under compression using a model of viscoelasticity. We validate the apparatus as well as the method of deconvolution by indenting bulk polytetrafluoroethylene and estimate mechanical properties of SAMs of different chain length and head group. The approach adopted here is able to distinguish in terms of mechanical properties a bulk polymer from a SAM and also between two SAMs of similar but subtly different structure.

Polytetrafluoroethylene (PTFE) films prepared by F2-laser deposition

Thin films of polytetrafluoroethylene (PTFE) were prepared by pulsed-laser deposition (PLD) from bulk PTFE targets using 157 nm F 2 -laser radiation. The films were analyzed by means of optical polarization microscopy, stylus profilometry, XPS, XRD, FTIR spectroscopy, and by capacitance measurements. The effect of substrate temperature, T s , on the morphology and crystallinity of the films was studied. Films treated at sufficiently high T s consist mainly of spherulite-like crystallites. Films with a thickness of more than about 155 nm are continuous, pinhole-free, well adherent to the substrate, and have a composition which is similar to that of the target material. The minimum film thicknesses and deposition rates are much lower than those achieved with pressed PTFE powder targets using 248 nm KrF-laser ablation. This is related to the different deposition mechanisms. Film formation based on KrF-laser ablation of pressed powder targets is mainly related to the condensation of large particulates transferred in a particle jet from the target to the substrate. F 2 –laser ablation and film formation seems to be based on the ablation and condensation of small fragments. Correspondingly, the morphology, crystallinity, and the optical and dielectrical properties of films significantly differ from each other.

Enhanced wear resistance of gamma-irradiated PTFE and FEP polymers and the effect of post-irradiation environmental handling

The wear resistance of bulk polytetrafluoroethylene (PTFE) and fluorinated ethylene propylene (FEP) fluoropolymer pin samples when sliding against polished steel countersurfaces is shown to be improved by over two orders of magnitude through the use of gamma irradiation. Wear rates were found to drop monotonically with increasing irradiation dose for both PTFE and FEP, with PTFE having a stronger dose response achieving two order-of-magnitude wear rate reduction within a 5 Mrad dose while FEP required a 30 Mrad dose to achieve similar reductions. Possible wear reduction mechanisms of irradiated fluoropolymers via crosslinking and scission are discussed. Though the effect of environment was less clear for PTFE, post-irradiation heated vacuum storage intended to enhance crosslinking further increased the wear resistance of FEP while accelerated aging potentially causing oxidative scission resulted in partial loss of radiation-induced wear resistance.

高周波スパッタリングにより作製したフッ化カーボン膜の化学構造と機械的特性の評価

A frictional durability and mechanical properties of the polytetrafluoroethylene (PTFE) thin films prepared by RF sputtering were estimated by tensile test, and the chemical structures of these films were estimated by x-ray photoelectron spectroscopy (XPS) analysis. The values of the tensile modulus and the breaking strength of the PTFE thin film were 25150 MPa and 545 MPa, respectively. These values were much smaller than those of the bulk PTFE. The mechanical properties of the PTFE thin film were influenced by the heat treatment. Although the tensile modulus and the breaking strength increased with the temperature of the heat treatment, the breaking strain decreased. The breaking strength and the breaking strain decreased with the heat treatment more than 200°C. These results indicate that the excessive cross linking structure in the PTFE thin film due to the heat treatment caused brittleness of the film. Although the frictional durability of the PTFE thin film was increased by the heat treatment within 200°C, it was decreased by the heat treatment at 300°C.

Preparation of Diamond-Like Carbon Polymer Hybrid Films Using Filtered Pulsed Arc Discharge Method

Novel non-stick and hard coating materials, diamondlike carbon polymer hybrids (DLC-p-h), were prepared with the filtered pulsed arc discharge (FPAD) method using a graphite polymer cathode. Polydimethylsiloxane (PDMS) and polytetrafluoroethylene (PTFE) were used as sample polymers for this new type of material. The properties of resulting DLC-polysiloxane (DLC-PDMS-h) and DLC-Teflon (DLC-PTFE-h) hybrids can be changed by adjusting the process parameters. DLC-PDMS-h films with striking nonstick properties were prepared. These films were hydrophobic, they could not be marked with common permanent marker pens and the adhesion of commonly used adhesive tapes was very low. The best measured water contact angles and droplet sliding angles were 112° and 3°, respectively. The peeling force in the 180° back peel test was over 100 times lower for DLCPDMS-h than for bulk PTFE. In contrast to common non-stick materials, DLC-PDMS-h films were very hard, Vickers hardness up to 70 GPa depending on the amount of polymer component. For example, a combination of 26 GPa hardness and 109° water contact angle was easily achieved. The elemental composition of these films was determined with elastic recoil detection analysis and the sp3 fraction with electron spectroscopy for chemical analysis.

高周波スパッタリングにより金属基板上に形成したポリテトラフルオロエチレン（ＰＴＦＥ）薄膜の機械的特性

Scratch durability of the thin films sputtered from polytetrafluoroethylene (PTFE) on copper and nickel substrates were evaluated using a pin-on-disk type apparatus. The sputter deposition rate of the PTFE thin film was faster than that of other polymers such as LDPE, HDPE, PMMA, Nylon-6, and PI. Surface of the PTFE thin film was smooth. The scratch durability of the PTFE film deposited on the copper substrate showed higher value than that on the nickel substrate. The friction and scratch durability is related to hardness of the metal substrates and adhesion strength between the PTFE film and the metal substrate. The adhesion strength between the PTFE film and evaporated metal films was higher than that between the bulk PTFE and the metal thin films. This result was estimated to be due to the difference of chemical bonding state between the PTFE thin film and the bulk PTFE.

Hot-wire chemical vapor deposition (HWCVD) of fluorocarbon and organosilicon thin films

HWCVD affords the capability to synthesize fluorocarbon and organosilicon thin films. These two classes of materials are of interest for a wide range of applications, including low dielectric constant coatings for microelectronic interconnection, ‘dry’ photoresists, directly patternable dielectrics for lithographic production of integrated circuits, insulating biomaterials for implantable devices with complex topologies and small dimensions, low friction coatings, and semipermeable membranes. HWCVD from hexafluoropropylene oxide (C3F6O) dramatically reduces cross-link and defect concentrations in fluorocarbon coatings, producing films which are spectroscopically indistinguishable from bulk polytetrafluoroethylene (PTFE, Teflon™). Organosilicon films can be deposited from cyclic precursors such as octamethylcyclotetrasiloxane (D4) at extremely high rates (>2 μm/min) by HWCVD. The bonding structure of HWCVD organosilicon films is substantially different from both their plasma enhanced CVD (PECVD) counterparts and bulk siloxane polymers, such as poly(dimethysiloxane) (PDMS).

Chemical composition and charge stability of highly crystalline pulsed-laser-deposited polytetrafluoroethylene films on metal substrates

KrF excimer-laser ablation of sintered-powder polytetrafluoroethylene (PTFE) targets is used for the deposition of high-quality PTFE films on metallic microstructures and metal backplates for electroacoustic applications. The films are found to be highly crystalline, consisting of large spherulites with diameters up to 1 mm. X-ray photoelectron spectroscopy of the films revealed the chemical similarity of press-sinter target pulsed-laser-deposited films with bulk PTFE. Negatively charged PTFE films on stainless steel backplates exhibit an exceptional charge stability with practically no decrease of the surface potential up to 225 °C in open-circuit thermally stimulated discharge.

Surface modification of polytetrafluoroethylene with tetraethoxysilane by using remote argon/dinitrogen oxide microwave plasma

The use of remote microwave plasma for the polymerization and deposition of tetraethoxysilane on the surface of polytetrafluoroethylene was investigated using a mixture of Argon and dinitrogen oxide as carrier gas. Layers with thicknesses of 0.5–3 μm were obtained, differing in chemical composition, surface energy, and flexibility/brittleness, depending on the plasma power and both the treatment and aging times. In general, milder treatments and shorter aging times resulted in higher contents of organic structural elements in the layers and greater flexibility and surface energy. Anchoring between the layers and the bulk polytetrafluoroethylene was at least partially caused by fibrils interconnecting the two components. These results were obtained by X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy in the attenuated total reflection mode, contact angle measurements, and scanning electron microscopy combined with energy dispersive X-ray analysis. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1207–1216, 2000

Pulsed-laser deposition of crystalline Teflon (PTFE) films

Thin films of crystalline polytetrafluoroethylene (PTFE) were prepared by pulsed-laser deposition using 248 nm UV-excimer-laser radiation. Pressed powder pellets and bulk PTFE have been employed as target material. The films were analyzed by means of optical polarization microscopy, stylus profilometry, capacity measurements, XRD, and IR spectroscopy. The effect of substrate temperature T s on the morphology and crystallinity of the films was studied. Films deposited from pressed powder targets at sufficiently high T s consist mainly of spherulite-like microcrystallites. These films are continuous, pinhole-free, well adherent to the substrate, and have a composition which is similar to that of the target material. It is suggested that film formation is based on laser-assisted material transfer with subsequent melting and crystallization. They are superior to films deposited from PTFE bulk targets, cut from a solid rod, with respect to film morphology, deposition rate, film cohesion, and optical and electrical properties.

Flexible fluorocarbon wire coatings by pulsed plasma enhanced chemical vapor deposition

A method to coat thin wires, 25 μm in diameter, with fluorocarbon material that is flexible and conformal has been achieved using pulsed plasma enhanced chemical vapor deposition (PECVD). This process enables the chemical composition of the films to be tailored in order to achieve similar stoichiometry and chemical composition to bulk polytetrafluoroethylene [PTFE, (CF2)n, Teflon™]. The deposited film had a F/C ratio of 1.9 and a CF2 fraction of 65%. In comparison, a film deposited under continuously applied power had a F/C ratio of only 1.6 and a CF2 fraction of 32% and was found to form brittle wire coatings. The flexibility of the pulsed PECVD film was consistent with its connectivity number of 2.1 corresponding to an underconstrained, flexible material. In addition, the connectivity number for the brittle film was 2.5, consistent with an overconstrained brittle network.

Growth of fluorocarbon polymer thin films with high CF2 fractions and low dangling bond concentrations by thermal chemical vapor deposition

Thermal chemical vapor deposition was used to deposit fluorocarbon films with chemical resemblance to bulk polytetrafluoroethylene. X-ray photoelectron spectroscopy revealed that the films deposited from thermal decomposition of hexafluoropropylene oxide had fluorine to carbon ratios of 2.0 and CF2 fractions of 90% along with 10% of CF3 and CF moieties. Electron spin resonance results found the dangling bond density to be 1.2×1018 spins/cm3, low compared to conventional plasma polymerized films. Low dangling bond densities were achieved by using a clean source of CF2 in the absence of plasma source.

Preparation and properties of highly oriented polytetrafluoroethylene films

Very thin, highly oriented and crystalline films of polytetrafluoroethylene (PTFE) can be deposited onto smooth surfaces by slowly sliding under load a piece of bulk PTFE on them at a high enough temperature. They consist of very long, straight and crystalline ribbons, which may almost completely cover the substrate. Film morphologies are presented. Physical properties and possible chemical modification of these films in order to prepare conjugated polymers are briefly discussed, as well as some problems related to the deposition of highly oriented organic or polymeric overlayers on these PTFE films.

Influence of substrate material and ion bombardment on plasma‐deposited fluorocarbon thin films

AbstractThe influence of substrate material and ion bombardment on fluorocarbon thin films deposited using a C2F6 glow discharge in an rf, parallel plate reactor was investigated. Monitoring of the plasma process by optical emission spectroscopy indicated that the dominant species in the glow discharge was CF2. Studies of bulk polytetrafluoroethylene (PTFE) and plasma‐polymerized fluorocarbon thin‐film samples in an XPS system demonstrated that the formation of non‐CF2 species can be induced by ion bombardment of CF2 molecules. Characterization of the deposited fluorocarbon films by XPS found that the F/C ratio and CFx distribution (0 < x < 3) in the films were dependent on processing conditions. Fluorocarbon films deposited simultaneously onto Al, glass, steel, and PTFE substrates using a C2F6 plasma and a graphite sputter target had measurably different F/C ratios, with the F/C ratio of the films deposited onto the Al substrates consistently lower than the F/C ratios of the films deposited onto the other substrates. When a C2F6 plasma was used without a graphite target, the F/C ratio in the film was constant, but the CFx distribution was different for each of the substrate materials. Analysis of the plasma‐polymerized films by TEM revealed that localized growth of fluorocarbon particles occurred during the initial stages of deposition, consistent with an activated growth mechanism. Differences in the F/C ratio for films deposited onto the various substrate materials were attributed to the interaction of the fluorocarbon plasma with the exposed surface of the substrate prior to complete coverage by the polymeric film. © 1994 John Wiley & Sons, Inc.

Applications of fluorocarbon polymers in micromechanics and micromachining

Several thin-film deposition and etching techniques of the polymer fluorocarbon are investigated and the resulting thin-film properties will be compared with those of commercially available bulk polytetrafluoroethylene. The most promising deposition technique is performed in a conventional reactive ion etcher using a carbonhydrotrifluoride (CHF3) plasma. By changing the deposition parameters, control of the properties and step coverage of the deposited thin films within a certain range is possible, eg., uni-directional and conformal step coverage of deposited thin films can be obtained. Etching is performed with the help of an evaporated aluminium oxide mask using an oxygen, nitrogen, or sulfurhexafluoride plasma for isotropic etching, or a CHF3 plasma giving a directional etch profile. The combination of the unique properties, deposition and etching techniques make fluorocarbon thin films a promising tool for micromachining; a number of applications will be discussed and demonstrated.

Wear of polytetrafluoroethylene: some crystallographic observations

When polytetrafluoroethylene (PTFE) discs are slid against EN24 steel, a transition in wear rate occurs after approximately 0.1 km of sliding. In the post-transition stage, the wear rate increases steadily up to a sliding distance of approximately 3 km after which it stabilizes. Structural characteristics of the worn surface derived from X-ray diffraction studies indicate that in the post-transition stage, a close correlation exists between the volumetric shrinkage of the unit cell and the wear rate. The shrinkage along the crystal-lographic a-axis, which can promote subsequent easy sliding of the polymer chains against each other, is found to be nearly twice the shrinkage along the crystallographic c-axis. Increase in the average crystallite size initiated by the sliding process does not, however, exhibit further progressive increase with sliding. The wear debris is less dense than the bulk PTFE. X-ray data from the debris indicate a lack of long range order, a reduction in crystallite size and an enlargement of the unit cell. Scanning electron micrographs show the simultaneous presence of crystalline and less crystalline fractions in the debris.

Effect of temperature on the transfer film formation in sliding contact of PTFE with stainless steel

The transfer of polytetrafluoroethylene (PTFE) to AISI 316 stainless steel during the first ten unidirectional traverses at room temperature, 100 °C and 200 °C was investigated. The amount of transferred PTFE was determined by detecting fluorine on the counterface utilizing the resonance of the nuclear reaction 19F(p,αγ) 16O at a proton energy of 340 keV. The transfer of PTFE was observed to increase with increasing temperature and pin load, the deposition rate being the highest in all cases during the first traverse. During subsequent traverses, the transfer of PTFE still occurred and a constant deposition rate at a given temperature and nominal pressure was observed. The temperature dependence of the amount of deposited PTFE was modelled using the concept of a temperature enhancement factor, which was found to be independent of the number of traverses and was a function of temperature only. This indicates that bulk PTFE rather than the interface properties were affected by the increased temperature.

Adhesion studies of metals on fluorocarbon polymer films

Adhesion of metal films to several fluorocarbon polymer films is studied for Cu, Cr, Ti, Al, and Au. The polymers include polytetrafluoroethylene (PTFE), fluoroethylenepropylene (FEP), and a copolymer containing a perfluoroalkoxy group (PFA), all deposited on Cr/SiO2 substrates by spin coating. Peel strengths of the metal strips on these polymers are compared and are taken as measures of the metal–polymer adhesion. Among the polymers, FEP gives the highest peel strengths to metals, with PTFE the lowest. Among the metals, Ti gives the highest peel strength for each polymer, followed by Cr, with Cu being the lowest. The peel strengths for Ti on FEP, PFA, and PTFE are 85, 75, and 20 g/mm, respectively. Those for Cu to the polymers are around 5 g/mm or less. The strong adhesion for the metals on both FEP and PFA is attributed to the high concentration of carbon sites with three fluorine neighbors, by considering the electronegativities among the various carbon sites in the polymer chains. Among the metals, some correlation with the electronegativity is seen. Ti shows, in addition, penetration into the polymers, contributing to the adhesion with all three polymers and resulting in shifts in binding energy for the C 1s electrons of the CF2 sites. An enhanced adhesion is also seen using a presputtering treatment of the PTFE films prior to the deposition of metal. The increase in peel strength, however, is smaller than that of the bulk PTFE.

The transfer of polytetrafluoroethylene studied by x-ray photoelectron spectroscopy

A polytetrafluoroethylene (PTFE) sphere of radius 4.8 mm was rubbed against nickel and S-Monel at speeds from 0.94 to 94 mm s −1 and at loads from 0.19 to 3.9 N. The transfer film of PTFE on the metal was examined with X-ray photoelectron spectroscopy. In all cases the film was found to be indistinguishable from bulk PTFE. A trace of metal fluoride was observed whether the rubbing took place on oxidized or atomically clean metal. The film was of the order of a molecule thick for the entire range of loads and did not increase with repeated passes over the same rubbed area. An erratic increase in thickness at rubbing speeds above 10 mm s −1 was taken as evidence of random transfer of bulk material.