PTFE Surface Research Articles

Hole metallisation technology for microwave printed circuit board

This research study investigates the hole metallisation processes of the microwave printed circuit board. During the study, the poly(tetrafluoroethylene) (PTFE) wall of the holes was modified by sodium naphthalene solution. Owing to the disruption of the C–F bond by the sodium atoms on the PTFE surface transforming C– dangling bonds, the surface energy of the PTFE increased from about 20 to 60–70 mN cm−1. The study employed XPS analysis to examine the modification mechanism. The results of the authors' study show peel strength of ∼2·03 N cm−1 between the copper layer and the sample treated with sodium naphthalene solution within the time range of 20–30 s.

Hydrophilic treatment poly(tetrafluoroethylene) reinforced sulfonated poly(ether ether ketone) composite membrane for proton exchange membrane fuel cell application

A reinforced composite membrane based on SPEEK (sulfonated poly ether ether ketone) and porous PTFE substrate (polytetrafluoroethylene) is fabricated and investigated for proton exchange membrane fuel cell application. In order to improve the combination between SPEEK polymer and PTFE matrix, PTFE substrate is hydrophilically pretreated by naphthalene sodium solution. The experimental results indicate that SPEEK can impregnate into treated PTFE substrate (abbreviated as trPTFE) more easily. The variation of PTFE surface property before and after treatment is characterized by water contact angle experiment and ATR-FTIR technique. The impregnated status of SPEEK polymer in PTFE matrix is also characterized by ATR-FTIR. According to the appearance photo of two composite membranes, it is showed that SPEEK/trPTFE composite membrane has more uniform and homogeneous morphology. Moreover, the mechanical property of SPEEK/trPTFE composite membrane also has an advantage over pristine SPEEK membrane. Due to the reinforced effect of trPTFE substrate, thinner composite membrane can be applied in single cell evolution and achieves better performance as a result.

Dynamic contact angles on PTFE surface by aqueous surfactant solution in the absence and presence of electrolytes

This study presents the experimental results on dynamic contact angles of pure surfactants and surfactants with electrolyte solutions on PTFE (Teflon) surface. Dynamic advancing ( θ A) and receding ( θ R) contact angles measurements by the Wilhelmy plate technique were carried out for aqueous solution of three different surfactants Triton X-100 (TX-100), sodium dodecylbenzene sulfonate (SDBS), and cetyltrimethylammonium bromide (CTAB). The same measurements in the presence of different electrolytes NaCl, Na 2SO 4, and CaCl 2 for ionic surfactants (SDBS and CTAB) were also carried out to see the change in contact angle and wetting behavior. The presence of electrolytes changes the advancing contact angle as well as wetting properties of hydrophobic solid surface significantly even at very low surfactant concentration. Counter ion valency of the electrolyte is more important in reducing advancing contact angle on hydrophobic PTFE surface at very low concentration of ionic surfactants from CMC. Pure surfactants and ionic surfactants in the presence of electrolytes show a linear relationship between the adhesional tension and surface tension at air–water interface with different slope and intercept.

Surface analysis of long-distance oxygen plasma sterilized PTFE film

The influence of long-distance oxygen plasma sterilization on surface properties of substrate material, i.e., medical poly(tetrafluoroethylene) (PTFE), and aging effect of these sterilized PTFE film surfaces were investigated by contact angle measurement, mass loss determination, scanning electron microscopy (SEM) as well as bacterial adhesion and platelet adhesion measurements in vitro, respectively. The changes in chemical structure of sterilized PTFE film were followed using X-ray photoelectron spectroscopy (XPS). As a result of plasma sterilization oxygen-containing functional groups (such as C O and C O), especially the C O group are introduced into PTFE surfaces, and thus pronounced increases of surface free energy and surface wettability are presented when the sample positions are within 0–40 cm. The film surface wettability degrades little as the aging time continued as long as 190 days. At the same time, the minimal surface degradation and damage occur on the sterilized PTFE when the sample position is at 40 cm. Moreover, the antibacterial adhesion and blood compatibility of sterilized PTFE surface are enhanced and the optimal effects are also obtained at 40 cm. The essential reason may be due to the optimal equilibrium between surface wettability and surface damage, which is achieved at 40 cm. Overall, of the surface properties of long-distance oxygen plasma sterilized PTFE analyzed, the sterilization at 40 cm is optimal.

PTFE/polyamide thin-film composite membranes using PTFE films modified with ethylene diamine polymer and interfacial polymerization: Preparation and pervaporation application

Plasma polymerization of ethylene diamine (EDA) on PTFE film surfaces is applied to modify PTFE surfaces to become hydrophilic and to incorporate amino groups onto PTFE surfaces. The surface-modified PTFE films are utilized as substrates for interfacial polymerization of EDA and trimesoyl chloride to prepare PTFE/polyamide thin-film composite (TFC) membranes. The effect of plasma power for plasma polymerization on the morphology and performances of the PTFE/PA TFC membranes are examined and discussed. The presence of amino groups on the PTFE substrates provides chemical linkages between PTFE and PA layers in interfacial polymerization to make the PTFE/PA TFC membranes are stable for pervaporation separations. A high permeation flux of 1910 g/h m 2 and a separation factor of 290 are observed with the PTFE/PA TFC membranes for pervaporation dehydration on a 70 wt% isopropanol aqueous solution at 70 °C. This approach explores a new method to prepare PTFE-based TFC membranes via interfacial polymerizations. The prepared TFC membranes could be potentially utilized in pervaporation and nanofiltration separations.

Study of plasma modified-PTFE for biological applications: relationship between protein resistant properties, plasma treatment, surface composition and surface roughness.

PTFE samples were treated by low-pressure, O2 RF plasmas. The adsorption of BSA was used as a probe for the protein resistant properties. The exposure of PTFE to an O2 plasma leads to an increase in the chamber pressure. OES reveals the presence of CO, CO2 and F in the gas phase, indicating a strong etching of the PTFE surface by the O2 plasma. Furthermore, the high resolution C1s spectrum shows the appearance of CF3, CF and C-CF components in addition to the CF2 component, which is consistent with etching of the PTFE surface. WCA as high as 160° were observed, indicating a superhydrophobic behaviour. AFM Images of surfaces treated at high plasma power showed a increase in roughness. Lower amounts of BSA adsorption were detected on high power, O2 plasma-modified PTFE samples compared to low power, oxygen plasma-modified ones.

Surface functionalization of PTFE sheet through atmospheric pressure plasma liquid deposition approach

We demonstrated here fascicle copper (Cu) metallization of poly(tetrafluoroethylene) [PTFE] surface through an atmospheric pressure plasma liquid deposition [APPLD] technique to design the interface for high frequency electronic devices. We found that exposing with atmospheric pressure helium plasma to the PTFE surface covered with thin liquid film, containing both poly(4-vinylpyridine) as a metal ion trapping polymer and copper acetate, simultaneously offered the plasma-induced direct graft polymerization and the reduction of Cu2+. The modified surface was characterized by using several analytical techniques, including water contact angle measurement, X-ray photoelectron spectroscopy, and atomic force microscopy.

Neutralization kinetics of charged polymer surface

In case of photoemission spectroscopy of an insulating material the data obtained from the charged surface are normally distorted due to differential charging. Recently, we have developed a controlled surface neutralization technique to study the kinetics of the surface charging. Using this technique and the associated data analysis scheme with an effective charging model, quantitative information from the apparently distorted photoemission data from PTFE surfaces were extracted. The surface charging was controlled by tuning the electron flood current as well as the X-ray intensity. The effective model was found to describe the charging consistently for both the cases. It was shown that the non-linear neutralization response of differential charging around a critical neutralizing electron flux or a critical X-ray emission current was due to percolation of equipotential surface domains. The obtained value of the critical percolation exponent γ close to unity indicates a percolation similar to that of avalanche breakdown or chain reaction.

Wettability characteristic of PTFE and glass surface irradiated by keV ions

Commercial PTFE and soda lime glass were irradiated by keV O 3+ and F 4+. After irradiation, in contrast to the decrease of contact angle on PTFE, contact angle on glass increased apparently. SEM observation revealed that irradiation did not cause noticeable change in surface topological structure. XPS was used to investigate chemical structure changes on the surface. Defluorination effect and formation of oxygen containing group caused by irradiation were considered to the reason of more hydrophilic PTFE surface. On the surface of irradiated glass, more carbon contaminations were observed. The differences of underlying physical and chemical processes between the two kinds of samples are discussed.

Enhancement of the adhesive force of metal films on PTFE surface achieved by fast-atom-beam surface modification

We tried the method to increase the peel strength between thin film metals and various substrate materials using saddle field fast atom beam (FAB) sources. It is notable that the peel strength was increased more than several times for all substrates than those who were not modified by surface activation using FAB irradiation. Highest peel strength was observed at the coupling of Si and metals in both case of Ar irradiation and SF6 reactive etching by FAB. This surface activation technique was applied to the fabrication of microelectrodes for the detection of mouse nerve signals. The process is expected as one of the available techniques for pre-treatment of the film deposition for several electrical devices.

Analysis of Surface Sterilization and Properties of Medical Poly(tetrafluoroethylene) in Remote Argon Plasma

We have used a remote-argon-plasma reactor in which the active species can be separated at a special plasma field. Argon gas is used as the work gas. In this remote argon plasma, the distribution of electrons, ions, and radicals and germicidal effect (GE) of Escherichia coli on the surface of medical poly(tetrafluoroethylene) (PTFE) film are studied. Then surface properties of sterilized PTFE are investigated by water-contact- angle and mass-loss measurements, as well as scanning electron microscopy and X-ray photoelectron spectroscopy, respectively. The results show that the concentration of electrons and ions decrease rapidly with increasing the sample position, which approximate to 0 at 30 cm, whereas the concentration of radicals change little within 40 cm. Relatively high-purity radicals are obtained in afterglow zone. GE values reach 4.633 in the active discharge zone (0 cm) and exceed 3.769 within 40 cm under the conditions of plasma RF-power of 100 W, exposure time of 120 s, and argon flux of 20 cm3/min. But remote-argon-plasma sterilization (40 cm) makes the PTFE surface higher hydrophilicity than the direct-argon-plasma sterilization (0 cm) and does not give remarkable degradation and damages in terms of mass-loss and surface morphology. Moreover, the remote argon plasma contributes more effectively to the defluorination (F/C = 2.24) from the PTFE than the direct argon plasma (F/C = 2.48), and thus, more oxygen functionalities (e.g., C = O) are formed on remote-plasma-sterilized PTFE surface. The essential reason is that remote argon plasma can enhance interactions between radicals and PTFE surface, which are inhibited in the active discharge zone. These experimental results show that the remote argon plasma is more appropriate to surface sterilization of medical PTFE in obtaining superior surface properties.

Surface effects and electrochemical cell capacitance in desorption electrospray ionization

Time resolved measurements show that during a desorption electrospray ionization (DESI) experiment, the current initially rises sharply, followed by an exponential decrease to a relatively steady current. When the high voltage on the spray emitter is switched off, the current drops to negative values, suggesting that the direction of current flow in the equivalent DESI circuit is reversed. These data demonstrate that the DESI source behaves as a dc capacitor and that the addition of a surface between the sprayer and the counter electrode in DESI introduces a new electrically active element into the system. The charging and discharging behavior was observed using different surfaces and it could be seen both by making current measurements on a plate at the entrance to the mass spectrometer as well as by measuring ion current in the linear ion trap within the vacuum system of the mass spectrometer. The magnitude of the steady state current obtained without analyte present on the surface is different for different surface materials, and different capacitor time constants of the equivalent RC circuits were calculated for different DESI surfaces. The PTFE surface has by far the greatest time constant and is also able to produce the highest DESI currents. Surface properties play a crucial role in charge transfer during DESI in addition to the effects of the chemical properties of the analyte. It is suggested that surface energy (wettability) is an important factor controlling droplet behavior on the surface. The experimental data are correlated with critical surface tension values of different materials. It is proposed, based on the results presented, that super-hydrophobic materials with extremely high contact angles have the potential to be excellent DESI substrates. It is also demonstrated, using the example of the neurotransmitter dopamine, that the surface charge that develops during a DESI-MS experiment can cause electrochemical oxidation of the analyte.

Wetting Behavior of Aqueous Solutions of Binary Surfactant Mixtures to Poly(tetrafluoroethylene)

Measurements of the surface tension (γ LV) and advancing contact angle () on poly(tetrafluoroethylene) (PTFE) were carried out for aqueous solutions of cetyltrimethylammonium bromide (CTAB), cetylpyridynium bromide (CPyB), sodium decylsulfate (SDS), sodium dodecylsulfate (SDDS), p-(1,1,3,3-tetramethylbutyl) phenoxypoly(ethylene glycol)s, Triton X-100 (TX100) and Triton X-165 (TX165) and their mixtures. The results obtained indicate that the values of the surface tension and wettability of PTFE depend on the concentration and composition of the surfactants mixture. In contrast to Zisman finding, there was no linear dependence between cos and the surface tension of aqueous solutions of surfactants and their mixtures for all studied systems, but a linear dependence existed between the adhesional tension and solution surface tension for PTFE in the whole concentration range, the slope of which was –1, indicating that the surface excess concentration of surfactant at the PTFE–solution interface was the same as that at the solution–air interface for a given bulk concentration. It was also found that the work of adhesion of aqueous solutions of surfactants and their mixtures to PTFE surface did not depend on the type of surfactant, its concentration and composition of the mixture. This means that for the studied systems the interaction across PTFE–solution interface was constant, and it was largely of Lifshitz–van der Waals type. On the basis of the surface tension of PTFE and the Young equation and thermodynamic analysis of the work of adhesion of aqueous solutions of surfactants to the polymer surface it was found that in the case of PTFE the changes of the contact angle as a function of the total mixture concentration in the bulk phase resulted only from changes of the polar component of the solution surface tension.

Molecular Mobility of Peroxy Radicals at the Ends of Nonisolated Polystyrene Chains Tethered on the Solid Surface of Poly(tetrafluoroethylene) in a Vacuum

The molecular mobility of peroxy radicals at the ends of nonisolated polystyrene chains (NIPSOO) tethered on the solid surface of poly(tetrafluoroethylene) (PTFE) in a vacuum was investigated in the temperature range from 10 to 250 K by electron spin resonance spectroscopy (ESR). The train−tail transition temperature of the NIPSOO tethered on the solid surface of PTFE in a vacuum was estimated to be 200 K, which was 40 K higher than that of the peroxy radicals at the ends of the isolated polystyrene chains (IPSOO) (Sakaguchi, M.; Yamamoto, K.; Miwa, Y.; Shimada, S.; Sakai, M.; Iwamura, T. Macromolecules 2007, 40, 1708; ref 1) tethered on the solid surface of PTFE in a vacuum. The activation energy (12.2−14.9 kJ/mol) of the NIPSOO of the tail state was large value compared to that (8.3−9.2 kJ/mol) (Sakaguchi, M.; Yamamoto, K.; Miwa, Y.; Shimada, S.; Sakai, M.; Iwamura, T. Macromolecules 2007, 40, 1708; ref 1) of IPSOO of the tail state. The high transition temperature and the large activation energy of the NIPSOO compared to those of the IPSOO are probably due to nonisolated chains, which take place in contacts and pseudo entanglements with inter- and neighboring-polystyrene chains on the PTFE surface.

Cover Picture: Tuning Cell Adhesion on PTFE Surfaces by Laser Induced Microstructures (Adv. Eng. Mater. 12/2007)

AbstractThe cover shows living cells adhering to PTFE surfaces. These surfaces were microstructured by laser ablation without changing the distinct chemical properties of the material. More about tuning cell adhesion on PTFE surfaces can be found in the article by J. Reichert et al. on page 1104.

Plasma-chemical surface functionalization of flexible substrates at atmospheric pressure

We demonstrated here fascicle surface functionalization of poly(tetrafluoroethylene) [PTFE] sheet through an atmospheric pressure plasma liquid deposition [APPLD] technique to design the interface for improvement of copper plated layer adhesion. We found that radiation with atmospheric pressure plasma to the PTFE sheet covered with thin liquid film, containing both an ion trapping polymer and copper ion (Cu 2+), simultaneously brought about the direct polymer grafting onto the PTFE surface and Cu 2+ ion reduction to metallic Cu. The treated surface was characterized by water contact angle measurement, X-ray photoelectron spectroscopy, and atomic force microscopy.

Studies on surface modification of poly(tetrafluoroethylene) film by remote and direct Ar plasma

Poly(tetrafluoroethylene) (PTFE) surfaces are modified with remote and direct Ar plasma, and the effects of the modification on the hydrophilicity of PTFE are investigated. The surface microstructures and compositions of the PTFE film were characterized with the goniometer, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Results show that the remote and direct plasma treatments modify the PTFE surface in morphology and composition, and both modifications cause surface oxidation of PTFE films, in the forming of some polar functional groups enhancing polymer wettability. When the remote and direct Ar plasma treats PTFE film, the contact angles decrease from the untreated 108–58° and 65.2°, respectively. The effect of the remote Ar plasma is more noticeable. The role of all kinds of active species, e.g. electrons, ions and free radicals involved in plasma surface modification is further evaluated. This shows that remote Ar plasma can restrain the ion and electron etching reaction and enhance radical reaction.

Topological and chemical investigation on super-hydrophobicity of PTFE surface caused by ion irradiation

Super-hydrophobic PTFE surfaces were obtained by irradiation of 200 keV Xe + ion with the fluence of 6.2 × 1 0 13 ions/cm 2. The contact angle of water on such surface is as large as 161 ± 3 ° . SEM and XPS were used to investigate how the topological and chemical changes affect the wettability of the irradiated surface. Needle like structures at nanometer scale caused by irradiation are considered to be the reason of the super-hydrophobicity. The formation of oxygen containing group and defluorination effect on the treated surface are inferred to have negative contribution to the hydrophobic optimization of PTFE surface.

Detection of Attomole Amounts of Analyte by Desorption Electrospray Ionization Mass Spectrometry (DESI-MS) Determined Using Fluorescence Spectroscopy

We report the use of fluorescence spectroscopy to investigate the amount of material removed from a PTFE surface and detected during desorption electrospray ionization (DESI) mass spectrometry measurements. The fluorescence intensity before and after DESI analysis of rhodamine 6G is used to determine the amount of material removed from the surface per mass spectrum. Calculations indicate low attomole amounts are removed per linear ion trap mass spectrum.

Tribological and Mechanical Properties of Carbon Nanofiber-Filled PTFE Composites

The tribological and mechanical properties of carbon nanofiber (CNF)-filled polytetrafluoroethylene (PTFE) composites with different filler proportions were studied. The worn surfaces of PTFE and carbon nanofiber/PTFE (CNF/PTFE) composites were then examined with scanning electron microscope (SEM). The results show the friction properties of CNF/PTFE composites decreased then increased with the increasing content of CNFs, while the anti-wear properties of CNF/PTFE composites were much higher than that of pure PTFE. The best anti-wear property was obtained with the composite containing 2 wt.% CNFs. The wear volume loss of the composite contained 2 wt.% CNFs was only about 1/700 that of PTFE without CNFs under the condition of 150N and 1.4m/s. Meanwhile, the results also indicate that the mechanical properties of CNF/PTFE composites increased then decreased with the increasing filler concentration, and the composite contained 1 wt.% CNFs has the best mechanical properties. Compare to pure PTFE, the tensile strength and the elongation of CNF/PTFE composites increased about 20% and 70% respectively when the filler content is 1 wt.%. It was seen from the worn surfaces micrographs of PTFE and CNF/PTFE composites that CNFs greatly reduce the adhesive wear of PTFE.