Teflon Foil Research Articles

Improving Printability of Polytetrafluoroethylene (PTFE) with the Help of Plasma Pre-Treatment.

Polytetrafluoroethylene (PTFE) is a potential candidate for the fabrication of flexible electronics devices and electronics with applications in various extreme environments, mainly due to its outstanding chemical and physical properties. However, to date, the utilization of PTFE in printing trials has been limited due to the material's low surface tension and wettability, which do not ensure good adhesion of the printing ink at the level of the substrate. Within this paper, successful printing of PTFE is realized after pre-treating the surface of the substrate with the help of dielectric barrier discharge non-thermal plasma. The efficiency of the pre-treatment is demonstrated with respect to both silver- and carbon-based inks that are commercially available, and finally, the long-lasting pre-treatment effect is demonstrated for periods of time spanning from minutes to days. The experimental results are practically paving the way toward large-scale utilization of PTFE as substrate in fabricating printed electronics in harsh working environments. After 3 s of plasma treatment of the foil, the WCA decreased from approximately 103° to approximately 70°. The resolution of the printed lines of carbon ink was not time dependent and was unmodified, even if the printing was realized within 1 min from the time of applying the pre-treatment or 10 days later. The evaluation of the surface tension (σ) measured with Arcotest Ink Pink showed an increase in σ up to 40 < σ < 42 mN/m for treated Teflon foil and from σ < 30 mN/m corresponding to the untreated substrate. The difference in resolution was distinguishable when increasing the width of the printed lines from 500 μm to 750 μm, but when increasing the width from 750 μm to 1000 μm, the difference was minimal.

A smart textile fabric with two-way action

The aim of the paper was to develop a prototype of smart textile material with shape memory elements that give variable thermal insulation dependent on the emission-absorption of heat. Shape memory elements were made in the form of spirals of two-way action from nitinol (NiTi) one-way wire. Two groups of samples were made: active and non-active. The active spirals expand at temperatures lower than the characteristic inner state transition temperature and contract as the temperature becomes higher than the transient temperature, which was about 45℃. The non-active spirals do not change dimensions under the influence of heat supply. The material of the layered structure was prepared. The first layer consisted of cotton woven fabric and the second layer featured a system of NiTi spiral elements, while the final layer was made of a thin Teflon foil. The behavior of samples during absorption-emission of heat was studied. Temperature measurements were conducted using an infrared camera; samples were placed on a heater to ensure contact between the Teflon layer and the base, and the temperature was recorded at the sample surface (woven fabric) as a function of the heating time for both active and non-active samples. A theoretical model that makes it possible to determine the time variable thermal parameters of the smart textile material was developed. Good agreement between the experimental and theoretical results was received. The temperature on the surface of the active sample was approximately 10℃ higher at the end of heating than the temperature of the non-active sample after the same heating pattern.

Investigation of Load Transmission Throughout a Riveted Lap Joint

Results of comparative load transfer measurements and fatigue tests on riveted lap joints from Alclad sheets of a configuration representative of the aircraft fuselage are presented. Two different rivet squeeze force values were accounted for and in either case riveted specimens with the interfaying Teflon foil between the sheets to minimize friction, in addition to standard riveted joints without such a layer, were considered. The goal of the investigation was to recognize implications of friction between the mating sheets for the fatigue behaviour of riveted lap joints in order to derive riveting process dependent coefficients to be included in a fatigue life prediction model for this type of connections.

Sensitivity of double cantilever beam test to surface contamination and surface pretreatment

The double cantilever beam (DCB) test is one of the commonly used destructive tests to qualify structural adhesives joints. By measuring the force and the corresponding crack growth of the mode I—loaded specimen, the adhesive fracture energy, GIC, can be determined. Many parameters like adhesive joint thickness, mechanical properties of the adhesive, substrate thickness and stiffness and production quality influence the results of the DCB test.In this article the influence of surface modification due to contamination and surface pretreatment on the results of DCB tests is investigated. Different amounts of hydraulic oil as a typical surface contamination have been applied to a carbon fiber reinforced plastic (CFRP) substrate. Three different surface pretreatments of the CFRP (peel ply, teflon foil and atmospheric pressure plasma) have been investigated. The surfaces have been characterized by contact angle measurements and atomic force microscopy (AFM). Results of DCB tests are analyzed in relation to the fracture surface and compared with tensile strength results of single lap shear specimens.

Shock Initiation of Nano-Al + Teflon: Time-Resolved Emission Studies

Laser-launched flyer plates were used to impact-initiate reactive materials consisting of Al nanoparticles (50 nm) and Teflon microparticles (3 μm). The initiation process was probed with time- and wavelength-resolved emission spectroscopy. Teflon particle and Teflon foil samples without Al fuel were also studied. During ∼15 ns duration shocks produced by 50 μm thick flyers, Teflon was heated to a greater extent than Al. Al/Teflon underwent explosive chemical reactions lasting ∼500 ns at an impact velocity threshold of 1.0 ± 0.1 km/s. The Teflon samples emitted a continuum spectrum attributed to triboluminescence. C2 emission (Swan bands) from the powder Teflon could be detected at impact velocities of 0.7 km/s, after a few microseconds, presumably from gases trapped between the decomposing sample and the observation window, indicating that Teflon can be at least partially decomposed to carbon and fluorine. During the 15 ns shock, the Al/Teflon had almost the same emission temporal and spectral profile an...

High Yield, Reproducible and Quasi‐Automated Bilayer Formation in a Microfluidic Format

A microfluidic platform is reported for various experimentation schemes on cell membrane models and membrane proteins using a combination of electrical and optical measurements, including confocal microscopy. Bilayer lipid membranes (BLMs) are prepared in the device upon spontaneous and instantaneous thinning of the lipid solution in a 100-μm dry-etched aperture in a 12.5-μm thick Teflon foil. Using this quasi-automated approach, a remarkable 100% membrane formation yield is reached (including reflushing in 4% of the cases), and BLMs are stable for up to 36 h. Furthermore, the potential of this platform is demonstrated for (i) the in-depth characterization of BLMs comprising both synthetic and natural lipids (1,2-diphytanoyl-sn-glycero-3-phosphocholine (DPhPC) and L-α-phosphatidylcholine (L-α-PC)/cholesterol, respectively) in terms of seal resistance, capacitance, surface area, specific capacitance, and membrane hydrophobic thickness; (ii) confocal microscopy imaging of phase separation in sphingomyelin/L-α-PC/cholesterol ternary membranes; (iii) electrical measurements of individual nanopores (α-hemolysin, gramicidin); and (iv) indirect assessment of the alteration of membrane properties upon exposure to chemical stimuli using the natural nanopore gramicidin as a sensor.

Improved estimation of contact compliance via atomic force microscopy using a calibrated cantilever as a reference sample

A method to improve accuracy of surface compliance determination by atomic force microscopy is presented, based on using calibrated cantilevers as the reference samples. During each work session, a 1-D compliance map of a reference cantilever is calculated from force–indentation curves along its axis, by the standard ‘indentation mode’. An independent measurement of local compliance on the reference cantilever is obtained by 2-D imaging in constant deflection and using analytical equations based on its known geometry and material properties, called ‘imaging mode’. A re-mapping of the apparent (‘indentation mode’) to the true (‘imaging mode’) compliance is thus obtained, which is applied on ‘indentation mode’ measurements of an unknown sample. This method demonstrates correction in the right direction for a polystyrene plate and a Teflon foil reference samples. The method is then applied on an unknown sample of flat agarose gel patterned with spots of polylysine protein.

Electron spin resonance from semiconductor–metal separated SWCNTs

AbstractElectron spin resonance in the X band is reported for fully metal–semiconductor separated SWCNTs. For the experiments samples were immersed in ethanol or wrapped into a teflon foil. The response from the metallic tubes exhibits a strong asymmetry in the line shape whereas the asymmetry for the semiconducting (SC) tubes is comparatively small. In both cases the line widths are unusual small, of the order of 4 G. Particular attention is paid to SC nanotubes which exhibit a much stronger signal as compared to the metallic tubes. The signal intensity is nearly Curie like with a small enhancement beyond $1/T$ in the low temperature range. The $1/T$ behavior renders the ESR response unobservable at 300 K. The finite value for the asymmetry parameter in the SC tubes is assumed to originate from charges picked up during exposure to air or to ethanol.

Effects of Temperature and Sheet Thickness on Formability of AZ31 Magnesium Alloy

The formability of AZ31 magnesium alloy sheets, with two different thicknesses, has been investigated at room temperature and 250°C by means of Nakazima tests. The different straining conditions have been studied by using sheet blanks with several length to width ratios, and Forming Limit Diagrams were then obtained with and without using lubricant. As expected, an increase in temperature was observed to enhance the formality of the alloy. The formability increases also by increasing the thickness as well as by using Teflon foil as lubricant. The microstructure of the deformed samples was analysed by means of light optical microscope.

Role of the support material on laser desorption/ionization mass spectra

We report the results of experimental studies on the effects of sample supports in laser desorption/ionization mass spectrometry (LDI-MS). LDI time-of-flight (TOF) mass spectra obtained for C(60) and insulin samples deposited onto standard stainless steel substrate and/or onto some non-metallic materials (glass, scotch tape, floppy disc foil, Teflon foil, photocopy film), all recorded under identical, typical experimental conditions, have been compared with regard to their intensity and quality. The LDI investigations show that compared with stainless steel, glass and floppy disc foil sample supports boost (2-3.5 times) ion yields for C(60)(+) and C(60)(-) ions, respectively. The stainless steel and scotch tape sample supports are the best for the mass resolution of positive ions and the formation of (C(60))(n)(-) (n <or= 4) cluster ions, respectively. In the case of detection of insulin by matrix-assisted laser desorption/ionization (MALDI) we did not observe significant differences in sensitivity for the support materials tested. A mechanism of ion formation in the desorption plume is suggested.

Inkjet Printing of conductive silver tracks in high resolution and the (alternative) sintering thereof

We present different methods to improve the resolution of inkjet printed lines. The first is a direct method without surface treatment. Small droplets of a single picoliter have been inkjet printed directly onto a polymeric foil that has a surface energy smaller than that of common polymer foils. On the other hand the surface energy was high enough to form continuous tracks, which is usually the case when printing, for example, onto Teflon foil. The second method uses a combination of inkjet printing and hot-embossing. The latter technique is used to create microchannels in a polymer foil by pressing a master into the substrate, which is held above its glass transition temperature, after which an inkjet printer is used to dispense single droplets of a silver nanoparticulate ink over these as-formed channels. Subsequently, the channels will fill by means of capillary forces and afterwards sintering resulted not only in narrow tracks smaller than 10 &#x3BC;m, but also gave higher conductivity values than the conventional inkjet printed lines. Typically, conductivities up to 20% were revealed, which can be explained by a higher packing due to the capillary forces used for filling the channels.Moreover, we present an alternative technique to sinter in a selective method inkjet printed silver tracks on common polymer foils, by microwave radiation. This alternative technique is capable of a low temperature decomposition of the organic binding material that is around each metal nanoparticle. This results in the formation of conductive tracks. After applying this selective sintering technique, the features have a conductivity similar to conventional convection-radiation sintering, which is the most commonly used sintering technique at the moment.

Sample water removal method in volatile organic compound analysis based on diffusion through poly(vinyl fluoride) film

The humidity caught during air sampling or sample storage causes various problems during volatile organic compound (VOC) analysis and gives unreliable results. In this study, water vapour diffusion capacities through poly(vinyl fluoride) Tedlar, fluoroethylene propylene Teflon and Flex foil film were compared. A new approach to humidity removal has been tested for moderately polluted atmospheres. This approach consists in using the water vapour diffusion property of Tedlar film to remove humidity from bag samples containing a mixture of ten VOCs at 500 ppbv each in a 70% relative humidity atmosphere. The sampling bags were placed in a chamber flushed by a dry air stream at less than 5% relative humidity. After a few hours in the chamber, the samples in the Tedlar bags were dry (relative humidity <5%) and did not show significant VOC loss. This sample water removal (SWR) method is especially interesting as a pretreatment before air sampling on water sensitive adsorbents.

Effects of ambient versus reduced UV‐B radiation on high arctic Salix arctica assessed by measurements and calculations of chlorophyll a fluorescence parameters from fluorescence transients

A UV‐B exclusion‐experiment was conducted in the high Arctic Zackenberg, NE Greenland, in which Salix arctica leaves during most of the growing season were fixed perpendicular to the solar zenith angle, thereby receiving maximal solar radiation. Covered with Teflon and Mylar foil, the leaves received approximately 90 and 40% of the ambient UV‐B irradiance, respectively. The effects were examined through recordings of chlorophyll a fluorescence transients, determination of biomass and analysis of total carbon and nitrogen content and amount of soluble flavonoids in the leaves. The processing of light was analysed by means of the chlorophyll a fluorescence transient, using the so‐called JIP test, as evolved by Reto J. Strasser and his coworkers. Reduction of the UV‐B irradiance caused a rise in many of the fluorescence parameters during July, but not in August (late season). Thus increases in the efficiency that an absorbed photon will be trapped by the PSII reaction centre with the resultant reduction of QA to QA– (ET0/ABS = FV/FM) and the efficiency that an electron residing on QA– will enter the intersystem electron transport chain (ET0/TR0) were observed in reduced UV‐B. Moreover, estimated per cross‐section of leaf sample, the number of active PSII reaction centres (RC/CSM) and electron transport rate (ETM/CSM) and all performance indexes (PIABS, PICSo and PICSm) were increased in reduced UV‐B. The total soluble flavonoid content was highest in ambient UV‐B. The treatment effects on fluorescence parameters that were directly measured (e.g. F0 and FM) and those that were derived (e.g. quantum efficiencies, parameters per PSII reaction centres and per cross‐section of leaf sample) are discussed in relation to one another, in relation to daily and seasonal variation, and from the perspective of evaluating the relative importance of UV‐B of donor and acceptor side capacity in Photosystem II. In conclusion, the experimental set‐up and non‐invasive measurements proved to be a sensitive method to screen for effects of UV‐B stress.

On the analysis of the interlaminar strain-energy release rates in ring-fracture-test specimens

An approach to analyze delamination in a circular composite beam specimen loaded in bending is presented. First, an experimental investigation of the interlaminar fracture behavior of unidirectional glass fiber reinforced polyester under mixed mode (I/II, opening + sliding) loading conditions was performed. For this purpose, the ring-fracture-test was used. The test was derived from a modified unidirectional glass fiber reinforced polyester ring specimen, which originally was used for investigation of the interlaminar tensile strength. The ring-shaped fracture-test specimens were produced by filament-winding technology. The ring specimen contains a tangential starter-delamination crack, being initiated from a strip of Teflon foil, which was added during the winding process. A radial cut was made in each ring at the opposite side of the starter crack, realizing a kind of horseshoe specimen. During the test, this specimen was subjected to opening forces. The crack propagated along the fibers (in circumferential direction) in a symmetrical manner with respect to the starter foil. A linear-elastic fracture-mechanics model is applied to interpret the crack-mechanical data recorded during the ring-test. The value of the interlaminar fracture energy is considered as a function of the length of the propagating circular crack. The total strain-energy release rate is decomposed into opening (mode I) and shearing (mode II) components. The mode partitioning shows that the ring-fracture-test gives variable mixed mode (I/II) ratios. The obtained values of the strain-energy release rate are compared with finite-element analysis results. It is found that the ring-fracture-test represents a new and useful approach for investigating the mixed mode (I/II) fracture behavior of unidirectional glass fiber reinforced polyester.

Angular dependent optical properties from outdoor measurements of solar glazings

A method for careful outdoor characterization of the angular dependent solar transmittance of solar glazing is developed and used for investigating the performance of structured and antireflection treated glass. Two identical collectors are series connected in order to get an identical flow. The reference collector is always covered with a thin Teflon foil and the test collector is furnished with the investigated covers. The method is carried out in six steps: (1) The collectors are long term tested in order to get the collector parameters, especially the U-values. (2) The performances of the collector at a temperature close to ambient are monitored during a clear day. (3) The effect of heat losses is eliminated from the knowledge of the U-values, and the optical efficiencies of the collectors are derived. (4) The ratio between optical efficiency of the test — and the reference collector is calculated. (5) Both collectors are tested with a Teflon film, with well-known optical properties, as a cover and the relative optical efficiency is derived. (6) From the relative transmittance between the investigated glazings and Teflon, the absolute value of the angular dependent transmittance is derived. The results show good agreement with conventional optical characterization. The commercial antireflection treatment increases the solar transmittance by 4% and the annual output by 9%. The structured glass shows similar angular performance as a flat glass if the structure is faced outwards, but shows a lower transmittance for incidence angles exceeding 40° if the structure is faced inwards. This means that the annual performance is decreased by 4% by facing the structure inwards instead of outwards.

Cosmic muon tomography of pure cesium iodide calorimeter crystals

Scintillation properties of pure CsI crystals used in the shower calorimeter being built for precise determination of the π +→π 0e +ν e decay rate are reported. Seventy-four individual crystals, polished and wrapped in Teflon foil, were examined in a multiwire drift chamber system specially designed for transmission cosmic muon tomography. Critical elements of the apparatus and reconstruction algorithms enabling measurement of spatial detector optical nonuniformities are described. Results are compared with a Monte Carlo simulation of the light response of an ideal detector. The deduced optical nonuniformity contributions to the FWHM energy resolution of the PIBETA CsI calorimeter for the π +→ e + ν 69.8 MeV positrons and the monoenergetic 70.8 MeV photons were 2.7% and 3.7%, respectively. The upper limit of optical nonuniformity correction to the 69.8 MeV positron low-energy tail between 5 and 55 MeV was +0.2%, as opposed to the +0.3% tail contribution for the photon of the equivalent total energy. Imposing the 5 MeV calorimeter veto cut to suppress the electromagnetic losses, GEANT-evaluated positron and photon lineshape tail fractions summed over all above-threshold ADCs were found to be 2.36±0.05 (stat) ±0.20 (sys)% and 4.68±0.07 (stat)±0.20 (sys)%, respectively.

Time-resolved density measurements of x-ray-heated Teflon foils using absorption spectroscopy.

We report on time-resolved absorption line shape measurements of lithiumlike fluorine produced from x-ray heated Teflon foil targets. X-ray emission created by a separate gold target was used as a backlighter. The width of the F VII 2{ital p}-3{ital d} line, which is Stark broadened, is observed to vary in time. This linewidth is used to infer the time-dependent electron density of the plasma when the density falls below 10{sup 21} cm{sup {minus}3}. These measurements agree well with hydrodynamic code calculations of the plasma density.

Experiments on 3-D crack growth in uniaxial compression

A study of spatial crack propagation under uniaxial compression was undertaken in a brittle transparent plastic with artificially induced internal cracks. The specific issue addressed was whether there was a qualitative difference between 2-D and 3-D crack propagation. Fracture of heterogeneous materials (e.g., rocks) under uniaxial compression is produced by propagation of internal cracks towards the load, some of which propagate so extensively that they eventually split the material into columns. Experimental and theoretical studies of this phenomenon based on 2-D models (plates with through cracks.) showed that the extensive crack growth towards compression emerged from pre-existing (initial) defects such as through cracks in plates inclined to the compression axis, or cylindrical pores (e.g., [1-10]). The main point of these studies is that a single 2-D microdefect is capable of producing extensive crack growth sufficient to cause fracture. In reality however, pre-existing cracks are three-dimensional, which can result in a more complicated mechanism of their growth. A limited number of experiments: Adams and Sines [4] and Cannoo et al. [11], have been reported on studies of the growth of inclined disk-like cracks in uniaxially compressed transparent samples (from PMMA polimethilmethacrylate plastic). However, the dimensions of the PMMA samples used in these experiments were not sufficient to investigate the extensive crack growth. In order to study mechanisms of fracture in uniaxial compression, further experiments are required using sufficiently large samples which would provide enough room for extensive crack growth. In addition, the spatial interaction of several growing cracks has to be investigated. This paper reports the results of such experiments. 1. Sample preparation and experimental technique. In the experiments, parallelepiped samples made from transparent casting polyester resin "Polylite 61-209" with cross-section dimensions of 55 mm x 55 mm, and a height of 120 mm were used. When frozen to -17°C, this material is perfectly brittle, deforms without barrelling and has linear stress-strain behaviour up to its burst-like fracture. The mechanical properties evaluated during the tests are: Young's modulus _=_4GPa; uniaxial compressive strength _=_ 140MPa; fracture toughness _=_0.6MPa-m 1/2. Two methods of modelling the internal initial disk-like cracks were adopted: (1) embedding a thin disk-like inclusion into the resin block during casting. The inclusion consisted of two aluminium foil disks greased and put together and held within the sample by two cotton threads; (2) cutting two semi-circular slots of 0.3 mm thickness in two halves of the sample and then gluing the halves together (this method was used in [4]). In order to ensure the contact between the opposite faces of the crack, teflon or greased foil disks were inserted into the slots (According to the 2-D analysis [9], the initial cracks, i.e. voids with contacted lips are the strongest drivers of the extensive crack growth).

Generation and functional characterization of ovine bone marrow-derived macrophages

A method for the culturing and propagation of ovine bone marrow-derived macrophages (BMM) in vitro is described. Bone marrow cells from sterna of freshly slaughtered sheep were cultured in hydrophobic (teflon foil) bags in the presence of high serum concentrations (20% autologous serum and 20% fetal calf serum). During an 18 day culture period in the absence of added conditioned medium, and without medium change, a strong enrichment of mononuclear phagocytes was achieved. Whereas the number of macrophages increased four to fivefold during this time, granulocytes, lymphoid cells, stem cells and undifferentiated progenitor cells were reduced to <3% of their numbers at Day 0. This resulted in BMM populations of 94 ± 3% purity. These cells had morphological and histochemical characteristics of differentiated macrophages, and they performed functions similar to those of non-activated, unprimed human monocyte-derived macrophages. Thus, they avidly ingested erythrocytes coated with IgG of heterologous or homologous origin. They expressed a modest level of procoagulant activity, but upon triggering with lipopolysaccharide (LPS), a marked increase in cell-associated procoagulant activity was observed. LPS triggering promoted the secretion of interleukin-1, as evidenced by measurement of murine thymocyte costimulatory activity, and transforming growth factor-β. Using the mouse L929 cell cytotoxicity assay as an indication of tumor necrosis factor (TNF) activity, no TNF activity was detected in the same supernatants, a result possibly due to species restriction. BMM generated low levels of O 2 − upon triggering with phorbol 12-myristate 13-acetate (PMA). On the other hand, no O 2 − production was observed upon stimulation with zymosan opsonized with ovine or human serum. Using luminol-enhanced chemiluminescence (CL) as a more sensitive indicator of an oxidative burst, both PMA or zymosan were able to trigger CL, but the response was subject to partial inhibition by sodium azide, an inhibitor of myeloperoxidase. This points to non-macrophage cells contributing also to the CL response, and is consistent with the view that unprimed BMM elicit a low oxidative burst upon triggering with strong inducers of a burst. Our functional characterization now allows us to apply priming and activation protocols and to relate their effect to functional alterations.

Mathematical model for calculating fatigue resistance of welded joints and base material of construction steel for single-stage loading. I: Unixial and compound loading: Kliemand, W. Schweisstechnik (Berlin) 1989 39, (12), 561–564 (in German)

Results of comparative load transfer measurements and fatigue tests on riveted lap joints from Alclad sheets of a configuration representative of the aircraft fuselage are presented. Two different rivet squeeze force values were accounted for and in either case riveted specimens with the interfaying Teflon foil between the sheets to minimize friction, in addition to standard riveted joints without such a layer, were considered. The goal of the investigation was to recognize implications of friction between the mating sheets for the fatigue behaviour of riveted lap joints in order to derive riveting process dependent coefficients to be included in a fatigue life prediction model for this type of connections.