Teflon AF Research Articles

Spontaneous electrification of fluoropolymer-water interfaces probed by electrowetting.

Fluoropolymers are widely used as coatings for their robustness, water-repellence, and chemical inertness. In contact with water, they are known to assume a negative surface charge, which is commonly attributed to adsorbed hydroxyl ions. Here, we demonstrate that a small fraction of these ions permanently sticks to surfaces of Teflon AF and Cytop, two of the most common fluoropolymer materials, upon prolonged exposure to water. Electrowetting measurements carried out after aging in water are used to quantify the density of 'trapped' charge. Values up to -0.07 and -0.2 mC m-2 are found for Teflon AF and for Cytop, respectively, at elevated pH. A similar charge trapping process is also observed upon aging in various non-aqueous polar liquids and in humid air. A careful analysis highlights the complementary nature of electrowetting and streaming potential measurements in quantifying interfacial energy and charge density. We discuss the possible mechanism of charge trapping and highlight the relevance of molecular scale processes for the long term stability and performance of fluoropolymer materials for applications in electrowetting and elsewhere.

Site-selective immobilization of functionalized DNA origami on nanopatterned Teflon AF

Teflon AF acts as a negative e-beam resist, here utilized for immobilization of porphyrin-anchored single DNA molecules on nanopillars, and precise determination of individual label positions.

Properties of thin Teflon AF 2400 coatings deposited onto carbon fabric from solutions in supercritical carbon dioxide

For the design of hydrophobized conductive gas diffusion layers of the electrodes of polymercontaining fuel cells, of great interest is the method for the formation of a fluoropolymer film from fluoropolymer solution in supercritical carbon dioxide. The present work describes the systematic studies on the carbon-fabric-deposited Teflon AF 2400 coatings obtained by this method. The electrical and geometric characteristics of the coatings, their elemental compositions, and stabilities are studied. It is shown that supercritical carbon dioxide allows the deposited fluoropolymer to penetrate homogeneously into the depth of carbon fabric to form a uniform coating around single individual fibers. The optimum limits of variation in the Teflon AF 2400 amount upon production of the gas diffusion layers of polymer electrolyte, alkaline, and phosphoric acid fuel cells are determined.

Geometric Restriction of Gas Permeance in Ultrathin Film Composite Membranes Evaluated Using an Integrated Experimental and Modeling Approach

Gas permeation through ultrathin film composite (uTFC) membranes can be restricted by the pore size and porosity of the porous supports, resulting in a reduction in permeance. Although this geometric restriction has been demonstrated using empirical and computational models, a systematic experimental validation of the models is still lacking. This study addresses the gap by preparing a series of uTFC membranes comprising glassy perfluoropolymers (such as Teflon AF1600 and Hyflon AD80) as selective layers on top of a commercial poly(ether sulfone) (PES) microporous support and investigating the effects of the surface morphology and selective layer thickness on the gas permeance. The geometric restriction resulting from the porous support becomes more severe as the selective layer becomes thinner. For example, the PES support decreased the gas permeance of a 100-nm-thick Hyflon AD80 film by as much as 42%. The experimental data agreed well with the modeling results, which convincingly confirms that porous s...

Fabrication and effect study of microfluidic SERS chip with integrated surface liquid core optical waveguide modified with nano gold

A novel microfluidic chip with integrated Teflon AF1600 surface liquid core optical waveguide (LCW) modified with nano gold was proposed and fabricated in this article. Physical deposite method was used to integrate Teflon AF1600 LCW into microchannel. After that, the inner surface of Teflon AF1600 LCW was chemically modified at temperature of 40 °C, subsequent nano gold were in situ immobilied on the silanized inner surface of Teflon AF LCW precoated with a thin layer of poly(diallyldimethylammonium chloride) within microchannel by a chemical self-assembly method. Under the optimized conditions, the prepared microfluidic SERS chip exhibited high sensitivity for R6G with detection limit of 10−11 mol/L and SERS enhancement factor (EF) of 2.7 × 108. Compared to single nano gold SERS enhancement substrate within a microfluidic chip, the SERS detection sensitivity for R6G was improved 4 orders of magnitude. Apart from high SERS enhancement effect, the as-prepared integrated microstructure had extremely good SERS detection reproducibility and duration stability. Furthermore, it was successfully used to detect the bovine serum albumin (BSA), and exhibited excellent SERS response. The research showed great prospects and technical support for design and fabrication of integrated SERS microfluidic chip and sensitive detection of trace biochemical samples.

Low Voltage Electrowetting on Ferroelectric PVDF-HFP Insulator with Highly Tunable Contact Angle Range.

We demonstrate a consistent electrowetting response on ferroelectric poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) insulator covered with a thin Teflon AF layer. This bilayer exhibits a factor of 3 enhancement in the contact angle modulation compared to that of conventional single-layered Teflon AF dielectric. On the basis of the proposed model the enhancement is attributed to the high value of effective dielectric constant (εeff ≈ 6) of the bilayer. Furthermore, the bilayer dielectric exhibits a hysteresis-free contact angle modulation over many AC voltage cycles. But the contact angle modulation for DC voltage shows a hysteresis because of the field-induced residual polarization in the ferroelectric layer. Finally, we show that a thin bilayer exhibits contact angle modulation of Δθ (U) ≈ 60° at merely 15 V amplitude of AC voltage indicating a potential dielectric for practical low voltage electrowetting applications. A proof of concept confirms electrowetting based rapid mixing of a fluorescent dye in aqueous glycerol solution for 15 V AC signal.

Physical aging of glassy perfluoropolymers in thin film composite membranes. Part II. Glass transition temperature and the free volume model

Thin film composite (TFC) membranes for gas separation often comprise a thin selective layer of a glassy polymer, which, however, suffers from physical aging, i.e., gas permeance decreases with time. This study aims to provide a mechanistic understanding of the effect of physical aging on permeance reduction in TFC membranes. The Part I study reports gas permeances in two-layer TFC membranes comprising perfluoropolymers of Teflon® AF or Hyflon® AD with thicknesses of 50–400nm. In this Part II study, apparent glass transition temperature (Tg) of thin selective layers was determined in situ over time using a nano-thermal analysis (nano-TA). Physical aging decreases gas permeances and increases apparent Tg, and the rate of changes is more significant for thinner selective layers. For example, N2 permeance decreases from 1000 gpu to 550 gpu while apparent Tg increases from 160°C to 172°C after aging for 2000h in a membrane with 100-nm-thick Teflon AF1600. The measured Tg values are used to derive polymer fractional free volume and physical aging rate. A simplified free volume model is used to successfully correlate the gas permeance reduction with Tg increase during physical aging. Polymers with good stability of permeability should have low physical aging rate and high fractional free volume.

Physical aging of glassy perfluoropolymers in thin film composite membranes. Part I. Gas transport properties

Physical aging of thin film glassy polymers continuously decreases gas permeability, presenting a great challenge in designing membrane systems for long-term gas separation. Most studies on the effect of physical aging on membrane applications use freestanding thin films, which are often annealed above the polymer glass transition temperature (Tg) before gas permeability is determined. However, industrial membranes are often thin film composites (TFCs) comprising the thin film on top of porous polymeric supports, and they may not be annealed above the Tg. The objective of this study is to investigate the effect of physical aging of the selective layer on gas permeance and selectivity of TFC membranes to establish industrial relevance. Two-layer TFC membranes consisting of perfluoropolymers (including Teflon® AF1600 and Hyflon® AD) at various film thicknesses (50 – 400nm) on polyethersulfone porous support were prepared and determined for permeances of CH4, N2, H2 and CO2 at 35°C for over 1000h. Gas permeances decrease with time, and the decrease is more significant for larger penetrants and for membranes with thinner selective layers. For example, CH4 permeance decreases by 54% and 27% after aging for about 1400h in TFC membranes comprising 50-nm- and 370-nm-thick Teflon AF1600, respectively. The decrease of gas permeances over time in these TFC membranes is compared with that of freestanding films. This study is one of only a few to present the results of physical aging in industrial TFC membranes and to provide useful insights for practical membrane applications.

Impact of Heavy Hydrocarbons on Natural Gas Sweetening Using Perfluorinated Polymeric Membranes

Membranes that are resistant to heavy hydrocarbons are of particular interest in natural gas sweetening, the removal of acidic gases such as CO2 from methane. The perfluorinated polymers Teflon AF1600 and Hyflon AD60 are studied here for this purpose because of their unusual solvent resistant properties. The sorption of hexane and toluene vapor in both perfluorinated polymers was observed to follow standard dual-mode sorption behavior at activities less than 0.8, while multilayer absorption was observed for unity activity. However, the corresponding Henry’s law constants for both hydrocarbons were reduced compared to other classes of glassy polymeric membranes. This was attributed to the solvent resistant properties of the perfluorinated polymers. Under mixed gas conditions, it was observed that the CO2 permeability for both perfluorinated polymers was reduced compared to the single gas permeability, attributed to competitive sorption from CH4. However, CH4 permeability increased slightly for both membranes under mixed gas conditions. Adding hydrocarbon vapors to the mixed gas feed resulted in only small changes to the CO2 and CH4 permeability through both perfluorinated polymers, indicating both perfluorinated polymers have potential as hydrocarbon-resistant membranes in natural gas sweetening.

Laboratory-Scale Membrane Reactor for the Generation of Anhydrous Diazomethane.

A configurationally simple and robust semibatch apparatus for the in situ on-demand generation of anhydrous solutions of diazomethane (CH2N2) avoiding distillation methods is presented. Diazomethane is produced by base-mediated decomposition of commercially available Diazald within a semipermeable Teflon AF-2400 tubing and subsequently selectively separated from the tubing into a solvent- and substrate-filled flask (tube-in-flask reactor). Reactions with CH2N2 can therefore be performed directly in the flask without dangerous and labor-intensive purification operations or exposure of the operator to CH2N2. The reactor has been employed for the methylation of carboxylic acids, the synthesis of α-chloro ketones and pyrazoles, and palladium-catalyzed cyclopropanation reactions on laboratory scale. The implementation of in-line FTIR technology allowed monitoring of the CH2N2 generation and its consumption. In addition, larger scales (1.8 g diazomethane per hour) could be obtained via parallelization (numbering up) by simply wrapping several membrane tubings into the flask.

Durable Superhydrophobic Surfaces via Spontaneous Wrinkling of Teflon AF.

We report the fabrication of both single-scale and hierarchical superhydrophobic surfaces, created by exploiting the spontaneous wrinkling of a rigid Teflon AF film on two types of shrinkable plastic substrates. Sub-100 nm to micrometric wrinkles were reproducibly generated by this simple process, with remarkable control over the size and hierarchy. Hierarchical Teflon AF wrinkled surfaces showed extremely high water repellence (contact angle 172°) and very low contact angle hysteresis (2°), resulting in droplets rolling off the surface at tilt angles lower than 5°. The wrinkling process intimately binds the Teflon AF layer with its substrate, making these surfaces mechanically robust, as revealed by macroscale and nanoscale wear tests: hardness values were close to that of commercial optical lenses and aluminum films, resistance to scratch was comparable to commercial hydrophobic coatings, and damage by extensive sonication did not significantly affect water repellence. By this fabrication method the size of the wrinkles can be reproducibly tuned from the nanoscale to the microscale, across the whole surface in one step; the fabrication procedure is extremely rapid, requiring only 2 min of thermal annealing to produce the desired topography, and uses inexpensive materials. The very low roll-off angles achieved in the hierarchical surfaces offer a potentially up-scalable alternative as self-cleaning and drag-reducing coatings.

Theoretical modeling of a self-referenced dual mode SPR sensor utilizing indium tin oxide film

A prism based dual mode SPR sensor was theoretically modeled to work as a self-referenced sensor in spectral interrogation scheme. Self-referenced sensing was achieved by sandwiching an indium tin oxide thin film in between the prism base and the metal layer. The proposed sensor possesses two plasmon modes similar to long and short range SPRs (LR- and SR-SPRs) and we have analogically used LRSPR and SRSPR for them. However, these modes do not possess usual long range character due to the losses introduced by the imaginary part of indium tin oxide (ITO) dielectric function. One of the two plasmon modes responds to change in analyte refractive index while the other remains fixed. The influence of various design parameters on the performance of the sensor was evaluated. The performance of the proposed sensor was compared, via control simulations, with established dual mode geometries utilizing silicon dioxide (SiO2), Teflon AF-1600 and Cytop. The design parameters of the established geometries were optimized to obtain self-referenced sensing operation. Trade-offs between the resonance spectral width, minimum reflectivity, shift in resonance wavelength and angle of incidence were examined for optimal design. The present study will be useful in the fabrication of self-referenced sensors where the ambient conditions are not quite stable.

Activation of blood clotting on cationic biomaterials via factor VII activating protease (FSAP)

Event Abstract Back to Event Activation of blood clotting on cationic biomaterials via factor VII activating protease (FSAP) Claudia Sperling1*, Marion Fischer1, Manfred F. Maitz1*, Simona Grasso2*, Carsten Werner1* and Sandip M. Kanse2 1 Leibniz-Institut fuer Polymerforschung Dresden e.V., Institute Biofunctional Polymer Materials, Max Bergmann Center of Biomaterials, Germany 2 University of Oslo, Department of Biochemistry, Institute of Basic Medical Sciences, Norway Introduction: Factor VII activating protease (FSAP), a serine protease involved in coagulation[1], fibrinolysis and inflammatory processes[2] is known to be auto-activated on charged macromolecules. It is highly homologous to Factor XII, a main initiator of coagulation on negatively charged biomaterials. We hypothesize similar activation processes for FSAP on material surfaces with impact on biomaterial related thrombogenicity. Materials and Methods: Materials with varied surface charge were prepared, characterized and incubated with either fresh human whole blood or plasma to detect activation of FSAP as well as blood activation processes: 1. PEI (Poly(ethyleneimine) spin-coated on argon-plasma treated teflon AF, cationic); 2. SAM-COOH (self assembled monolayers with terminal carboxylic groups, anionic); 3. Glass (anionic); 4. Teflon-AF (spincoated on glass, no ionizable groups on surface). Blood from healthy donors was heparinized and incubated in a customized set-up for 3 hours. For additional FSAP inhibition experiments the inhibitory antibody mab570 was used. Subsequently blood and surfaces were analyzed for FSAP activity as well as for specific blood activation parameters: thrombin and fibrin formation (F1+2, FPA), platelet activation (PF4, cell adhesion) and immunologic reactions (CD11b, C5a, cell adhesion). Results and Discussion: Different activation processes on negatively and positively charged surfaces were observed: FSAP was exclusively activated on cationic PEI surfaces, not on anionic or hydrophobic, uncharged surfaces (Table 1) while contact activation was only detectable on anionic surfaces (glass, SAM-COOH). Table 1: FSAP activity in blood after 3 h incubation detected using a direct activity assay as well as FSAP inhibitor complexes [arb. units] Substantial coagulation activation (thrombin/fibrin formation) occurred on FSAP activating PEI and on FXII activating glass but not on Teflon-AF or SAM-COOH (Figure 1) due to a missing coagulation initiation on Teflon and missing platelet supported coagulation amplification on SAM-COOH[3]. The strong coagulation propagation on PEI was confirmed to be FSAP dependent with the implementation of an FSAP inhibitory antibody that diminished thrombin formation. Figure 1: Coagulation activation and fibrin formation on surfaces. Coagulation activation measured as TAT (Thrombin-antithrombin-complex, grey bars) and fibrin formation measured as FPA (fibrinopeptide A, white bars) Statistics: *: significantly different to all other samples. Insets: SEM photographs of surfaces (magnification 4000x; ESEM XL 30 FEG, FEI-Philips, Eindhoven, The Netherlands) Conclusion: We present a new hypothesis on blood activation claiming that on cationic surfaces FSAP gets activated and mediates thrombin amplification. Our experiments are relevant for the interaction of blood with surfaces but also for the role of FSAP in coagulation and immunology.

Alcohol selectivity and measurement of ethanol concentrations in liquors using Teflon® AF2400-coated gold-deposited surface plasmon resonance-based glass rod sensor

Abstract A gold (Au)-deposited surface plasmon resonance (SPR)-based glass rod sensor coated with an α-mercaptoethyl-ω-methoxy polyoxyethylene (PEG thiol) layer and a Teflon AF2400 overlayer with high selectivity for small molecules contained in aqueous solutions was developed. The PEG thiol layer forms a space (approximately 13 nm wide) for the analytes to accumulate between the Au film (45 nm thick) and the Teflon layer (approximately 12 μm thick). The water and alcohol content in the sample solutions pass selectively through the porous Teflon overlayer, accumulate in the PEG thiol spacer layer and are then detected through the SPR phenomenon. Cross-sectional scanning electron microscope imaging of the sensor was used to measure the thickness of the Teflon overlayer on the Au film. The sensor selectivity was then evaluated using aqueous solutions of various alcohols. The sensor responds reversibly to the concentrations of only monohydric alcohols. The response is faster than that of the Teflon AF1600-coated sensor as a result of the increased permeability and the reduced thickness of the Teflon AF2400 overlayer. The sensor maintains both its sensitivity and its selectivity for as long as 6 months. Direct measurement of the ethanol concentrations of aqueous ethanol solutions that were mixed with interference compounds is possible using this sensor. The ethanol concentrations of various liquors were measured directly. This sensor is a unique device with functions for both separation and detection of the analytes.

Thin-film composite membrane contactors for desorption of CO 2 from Monoethanolamine at elevated temperatures

Abstract Membrane gas solvent contactors are a hybrid approach that shows potential to be more efficient for carbon dioxide capture than traditional packed columns. Here, three non-porous composite membrane contactors are trialed for desorption of CO 2 from loaded Monoethanolamine (MEA) at temperatures 70 °C and above. These are non-porous poly (1-trimethylsilyl-1-propyne) (PTMSP), Polymer of Intrinsic Microporosity (PIM-1) and Teflon AF1600, all on a porous PP support. The CO 2 regeneration flux was shown to increase with temperature because of increasing driving force across the membrane. Similarly, the CO 2 flux increased with solvent Reynolds number because of increasing turbulence in the solvent boundary layer. The overall mass transfer coefficient for the three membrane contactors were calculated and demonstrated that desorption was a mass transfer limiting process, with over 90% of the resistance corresponding to the solvent boundary layer. The water vapor fluxes through the non-porous membrane contactors were also measured and highlighted that water permeation was greater than CO 2 for all three membrane contactor systems.

Comparison of thin film composite and microporous membrane contactors for CO2 absorption into monoethanolamine

Membrane gas solvent contactors show potential for carbon capture, because it incorporates the advantage of both solvent and membrane technology. Here, three thin film composite membrane contactors are trialed for the absorption of CO2 into monoethanolamine (MEA) solvent. These are prepared from coating dense poly (1-trimethylsilyl-1-propyne) (PTMSP), a Polymer of Intrinsic Microporosity (PIM-1) and Teflon AF1600 on a porous PP support. It was found that after 1h of operation, the PTMSP and PIM-1 membrane contactors provided the highest overall mass transfer coefficient, while Teflon AF1600 performance was lower. Comparison of the CO2 permeability through the membrane based on mass transfer resistance calculations showed that both PTMSP and PIM-1 had significantly hindered CO2 permeance compared to that expected from gas permeability measurements. This was due to the presence of water and MEA sorbed within the non-porous layer hindering the migration of CO2 through both membranes. Importantly, for both PTMSP and PIM-1 membranes water migrated over time from the dense layer into the porous support and wetted the pores. The Teflon AF1600 dense layer was resistant to water and MEA sorption and hence the permeation of CO2 through this layer was comparable to that expected from gas permeability measurements. Equally important, after 10h of operation no change in overall mass transfer coefficient was observed indicating that Teflon AF1600 was able to prevent water from wetting the porous PP support. Hence, for thin film composite membrane contactors to be effective for CO2 separation, the dense layer must have a high CO2 permeability as well as be resistant to water sorption.

A Solution-Processed Organic Thin-Film Transistor Backplane for Flexible Multiphoton Emission Organic Light-Emitting Diode Displays

An active matrix backplane based on solution-processed organic thin-film transistors (OTFTs) has been developed for flexible displays having multiphoton organic light-emitting diodes (OLEDs). The OTFT device has a bottom-gate/bottom-contact type structure consisting of a polyethylene naphthalate-based flexible substrate covered with patterned gate electrodes and a gate dielectric of UV-cured cardo-polymer. Teflon AF was used for a hydrophobic bank structure that defines active regions of the OTFTs, and the organic semiconductor was coated by solution shearing. The OTFT backplane fabricated here had $384 \times 128$ pixels at a resolution of 300 dpi; images and video were successfully displayed on the resulting flexible multiphoton-emission OLED display.

Continuous Flow Metathesis for Direct Valorization of Food Waste: An Example of Cocoa Butter Triglyceride.

The direct chemical conversion of cocoa butter triglycerides, a material available as a postmanufacture waste stream from the food industry, to 1-decene by way of ethenolysis is reported. The conversion of the raw waste material was made possible by use of 1 mol % of the [RuCl2(iBu-phoban)2(3-phenylindenyl)] catalyst. The process has been investigated in both batch and flow conditions, where the latter approach employs a Teflon AF-2400 tube-in-tube gas–liquid membrane contactor to deliver ethylene to the reaction system. These preliminary studies culminate in a continuous processing system, which maintained a constant output over a 150 min period tested.

Water permeability and competitive permeation with CO2 and CH4 in perfluorinated polymeric membranes

The permeability of water through polymeric membranes is of particular interest in gas separation, because of the high water vapor content found in many industrial applications. Polymeric membranes that are resistant to competitive sorption and plasticization by water are especially attractive, since they can reduce the need for gas pretreatment in many membrane applications. The perfluorinated polymers Teflon AF1600 and Hyflon AD60 are studied here for this purpose because of their strong hydrophobicity and unusual solvent properties. It was observed that water permeability through both perfluorinated polymers was of the same magnitude as CO2. Indeed, under the conditions studied, Teflon AF1600 was selective for CO2 over water. Such reverse selectivity for the CO2 – H2O gas pair has not been reported before for glassy polymeric membranes and reflects the very low solubility of water in the polymer. The water permeability through Hyflon AD60 was greater than that for CO2 with a minimum at 55°C. The change in both CO2 and CH4 permeability through Teflon AF1600 and Hyflon AD60 was investigated as a function of water activity in the feed gas to investigate the effects of competitive permeation. It was observed that CO2 and CH4 permeability in both membranes reduced with water activity. For both Teflon AF1600 and Hyflon AD60, the decrease in permeability of both gases with water activity was interpreted as water clusters blocking the diffusion of both CO2 and CH4 through the membrane.

Free Volume Profiles at Polymer–Solid Interfaces Probed by Focused Slow Positron Beam

The properties of materials involving polymer–solid interfaces are determined not only by the properties of the constituents but also by the interfacial region of the polymer near the solid, the so-called interphase. Here we report on positron annihilation lifetime spectroscopy (PALS) measurements of the free volume near the interface with a focused positron beam. The measurements were performed at an interface between a Teflon AF 1600 film and a 30 nm thick SiN membrane from the backside of a Si substrate which was locally etched away to expose the ultrathin SiN membrane. We were able to focus the positron beam onto the exposed region and to probe the SiN–Teflon AF 1600 interfacial region with low implantation energies, resulting in very narrow implantation profiles and excellent depth resolution. We found a pronounced decrease in orthopositronium lifetime close the interface. On the basis of modeling, we could estimate the interphase width and the average density increase in the interfacial region as ∼12 nm and 5–7%, respectively.