Dielectric properties of polytetrafluoroethylene films modified by direct current discharge

Dielectric characteristics of polytetrafluoroethylene (PTFE) films modified by direct current discharge at the anode and cathode have been studied as a function of frequency and temperature. It has been found that the dielectric constant increases slightly as a result of plasma treatment and weakly depends on temperature. It has been shown that the frequency dependences of conductivity at 20°C differ somewhat for the original and treated films, but the closer resemble one another at 80°C, with the difference in the critical conductivity indices becoming more significant.     

Direct-current discharge treatment of polytetrafluoroethylene films

The effect of treatment in a low-pressure dc discharge on the surface properties of polytetrafluoroethylene (PTFE) films modified at the anode and cathode was examined. It was found that the anode treatment of the films considerably improves the adhesive properties of the polymer and makes it possible to obtain substantially lower values of the contact angle and higher values of the work of adhesion and surface energy than in the case of other PTFE surface modification techniques. By means of IR and X-ray photoelectron spectroscopy, it was shown that discharge treatment at the anode and cathode noticeably increases the amount of oxygen-containing groups on the surface of the films.     

Adhesive properties of plasma-modified polytetrafluoroethylene films

A procedure was developed for the determination of the adhesion characteristics of the modified surface of thin polymer films, including those treated in a low-temperature plasma, with the use of the Scotch® 810 adhesive tape. The procedure comprises coating the surface to be studied by physical vapor deposition with an aluminum layer of ～100 nm thickness, making an adhesive joint of the film with the Scotch® 810 tape, and T-peel testing of the specimen. Using this procedure, the peel resistance of the initial PTFE film and the film modified at the cathode and the anode in dc discharge was measured.     

The oxidative modification of polypropylene surface in electrolytic-cathode atmospheric-pressure discharge

The effect of electrolytic-cathode atmospheric-pressure discharge in air on the surface of polypropylene immersed in a solution and on the hydrogen peroxide formation efficiency was studied. It was found that iron(II) sulfate admixtures lead to a substantial increase in the concentration of oxygen-containing groups on the surface and to a decrease in the concentration of hydrogen peroxide in the solution. A possible interpretations of the results is given.     

Effect of direct-current discharge treatment on the surface properties of chitosan-poly(L,L-lactide)-gelatin composite films

The surface of films made from a chitosan-poly(L,L-lactide)-gelatin mixture stabilized with a grafted-copolymer fraction has been modified by dc discharge treatment, as well as that of films made of the individual components. The surface properties of the films (wettability, surface energy), the chemical structure of surface layers, and their morphology have been examined by goniometric measurement of contact angles, X-ray photoelectron spectroscopy, and scanning electron microscopy.     

Effect of surface modification on the properties of plasma-polymerized hexamethyldisiloxane thin films

Plasma-polymerized hexamethyldisiloxane (pp-HMDSO) thin films have been deposited in a radiofrequency (RF) remote plasma-enhanced chemical vapor deposition (PECVD) system, on different types of substrates: silicon wafers, glass, quartz crystals, and chemiresistor structure. The as-grown thin films have been post treated in two types of reactive plasmas produced in SF₆ and O₂ gases. The effect of this surface modification on different properties of the as-grown pp-HMDSO thin film (chemical structure, elemental composition, surface morphology, film density and thickness, optical bandgap, and electrical resistivity) has been investigated. It is found that SF₆ plasma and O₂ plasma surface modifications of the as-grown pp-HMDSO thin film induce property changes different from each other. SF₆ plasma converted the as-grown pp-HMDSO film to a more porous material and caused a narrowing of its optical band gap of about 33%, while O₂ plasma induced a lowering of film electrical resistivity of about two orders of magnitude.     

Some fundamental measurements of the atmospheric-pressure,microwave-induced discharge

Measurements of several fundamental parameters in a microwave-induced atmospheric-pressure flowing plasma are presented. Optical and electrical measurements were performed on argon and argon/nitrogen plasmas in the region 1–7 cm outside the cavity, as the applied microwave power, and plasma composition were varied.The stability of the plasma, atomic emission from the argon support gas, and emission from the analyte species, are proportional to the electron density. The observed electron density was varied when the power was changed,-when an electrophilic species was added, and as the observation zone was moved relative to the microwave field. In all cases, the change in the emission signal followed the change in electron density.The electron temperature, as measured by the double-probe method, is related to the kinetic energy of the fastest-moving electrons in the plasma. It is unchanged by variations in power, plasma gas composition, flow rate, and is independent of the location of the probes relative to the cavity. The spectroscopic and electrical data are consistent with excitation by ion—electron radiative recombination.     

Alteration in the surface structure and properties of norbornene-ethylene copolymer films by direct-current discharge treatment

The effect of dc discharge on norbornene-ethylene copolymer films containing 30 and 60% norbornene was studied. It was found that plasma treatment leads to substantial changes in the surface properties of the copolymer, the enhancement of wettability, and an increase in the work of adhesion and surface energy, including its polar term. The change in the surface structure of the films was investigated by means of Fourier-transform IR spectroscopy. Transparent and colorless triplexes with a light transmission of 86–90% were prepared on the basis of the discharge-modified copolymer films and a cycloaliphatic epoxy resin.     

Chemical and physical modification and electret properties of polytetrafluoroethylene films

Composites with titanium oxide structures on the surface of a polymer matrix were prepared by preliminary plasma activation of polytetrafluoroethylene films, followed by chemical treatment with vapors of titanium tetrachloride and water. The chemical composition and structure of the modified film surface were studied by scanning electron microscopy, atomic force microscopy, and X-ray photoelectron spectroscopy. The stability of the formed surface charge increases in going from the initial film to the plasma-activated film, then to the film successively treated with vapors of titanium tetrachloride and water, and finally to the plasma-activated film treated subsequently with vapors of titanium tetrachloride and water. The modified polytetrafluoroethylene films are of interest as electrets with enhanced operation characteristics.     

Effect of organomodified layered silicates on the properties and structure of polytetrafluoroethylene

The physicomechanical and triboengineering properties and the structures of polymer composite materials based on polytetrafluoroethylene and layered silicates are studied. The triboengineering characteristics are substantially improved by the introduction of a small amount of layered silicates (2–5 wt %). It is found that the introduction of organomodified layered silicates leads to a considerable reduction in the friction coefficient, by an order of magnitude, and causes an increase in wear resistance (2000-fold). With the use of X-ray structural analysis and scanning electron microscopy, it is shown that, during friction loading, filler particles are localized on the friction surface, thereby hampering wear of the material.     

Change in the surface properties of poly(vinylidene fluoride) films by treatment in direct-current discharge

It has been found that treatment in dc discharge results in a substantial and time-invariant increase in the surface energy of poly(vinylidene fluoride) films. This effect is obviously due to the formation of oxygen-containing groups on the polymer surface, a fact that is corroborated by Fourier-transform IR spectroscopy and X-ray photoelectron spectroscopy data. It has been shown that dc discharge is more effective in altering the contact properties of the polymer surface than low-frequency glow discharge.     

Effect of the structural parameters of a series of fluoromonoacrylates on the surface properties of cured films

A series of fluorinated acrylates [F(CF₂)_q? (CH₂)_p? OCOCH?CH₂, where q = 8 and p = 2 ÷ 11) were synthesized and used as comonomers in the photopolymerization of acrylic systems. These fluoroacrylates were synthesized in a three‐step procedure through the radical addition of perfluoroalkyliodides to an unsaturated alcohol followed by their acrylation. The mixtures, containing up to 0.8% (w/w) of the comonomers, produced transparent films after UV curing; they showed changes in the surface properties as a function of the comonomer type and concentration. With contact‐angle and X‐ray photoelectron spectroscopy analyses, the relationship between the structure of the monomers and the surface properties of the UV‐cured films was investigated: the wettability decreased, depending on the length of the fluorinated group (q value) and the hydrogenated segment of the monomer (p value). © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 4227–4235, 2001     

Copper nanoparticles on the surface of ultradispersed polytetrafluoroethylene nanograins

Nanosized copper-containing particles stabilized on the surface of polymer nanograins were obtained by thermal decomposition of copper-containing precursors in a fluidized bed of ultradispersed polytetrafluoroethylene. Transmission electron microscopy showed that the average size of nanoparticles is 10–12 nm. The structure of the particles was determined by EXAFS, EPR, and X-ray powder diffraction. The copper nanoparticles consist of a core and a shell and are well structured. The core is copper metal, whereas the surface layer, which constitutes no more than 2% of the nanoparticle weight, is copper oxide.     

Mechanism of hydrogen peroxide formation in electrolytic-cathode atmospheric-pressure direct-current discharge

The kinetics of buildup of hydrogen peroxide in an atmospheric pressure direct-current discharge with a distilled-water cathode has been experimentally measured. A kinetic reaction scheme has been proposed and analyzed to calculate peroxide concentrations in accordance with experimental data.     

Wetting properties at the surface of iota-carrageenan-based edible films

Surface properties of edible films composed of a polymeric matrix of carrageenan in association with hydrophobic material were studied by contact angle measurements. The use of this technique not only in a static mode but also in a dynamic way enables investigation of surface hydrophobicity as well as surface wettability. The absorption flux inside the material can be estimated from the wetting kinetic, which can be very useful to quickly compare water barrier efficiency of the tested films. Comparison of carrageenan films with films containing known amounts of additives enables understanding and correlation of changes of the surface properties with the nature of used additives (glycerol used as a plasticizer, glycerol monostearate used as a surfactant, and fat) and their influence on the orientation of polymer chains at the surface during film formation. Very different responses were observed from one surface of the film (film-casting-support interface) to the other (film-air interface), which could be also attributed to the influence of the support on the polymer and to macromolecular orientation during drying after casting.     

The adhesive properties of polyfluoroolefin films modified by direct-current discharge

The influence of the treatment of various structures polyfluoroolefine films by the direct-current discharge at the anode and cathode on the properties of the surface (the value of the contact angles of wettability, work of adhesion, and surface energy and its polar and dispersive components) is studied. Measurements of the peel strength of plasma-treated films are conducted. It is shown that the direct-current discharge treatment makes it possible to substantially increase the peel strength of the polyfluoroolefin films.     

Effect of maleic anhydride‐grafted polytetrafluoroethylene on the tensile and tribological properties of blending polytetrafluoroethylene with polyamide‐6

Blending polytetrafluoroethylene (PTFE) to polyamide‐6 (PA6) with and without maleic anhydride‐grafted polytetrafluoroethylene (PTFE‐g‐MA) was produced in a corotating twin screw extruder, where PTFE acts as the polymer matrix and PA6 as the dispersed phase. The effect of PTFE‐g‐MA on the tensile properties and tribological propertiesof PTFE/PA6 polymer blends is studied. Results show that the structural stability and morphology of the blends were greatly improved by PTFE‐g‐PA6 grafted copolymers, which were formed by the in situ reaction of anhydride groups with the amino end groups of PA6 during reactive extrusion forming an imidic linkage. The presence of PTFE‐g‐PA6 in the PTFE continuous phase improves the interfacial adhesion, as a result of the creation of an interphase that was formed by the interaction between the formed PTFE‐g‐PA6 copolymer in situ and both phases. Compared with thePTFE/PA6 without PTFE‐g‐MA, the PTFE/PA6 with PTFE‐g‐MAhad the lowest friction coefficient and wear under given applied load and reciprocating sliding frequency. The interfacial compatibility of the composite prevented the rubbing‐off of PA6, accordingly improved the friction and wear properties of the composite. Copyright © 2009 John Wiley & Sons, Ltd.     

Tin oxide coating on polytetrafluoroethylene films in aqueous solutions

Polytetrafluoroethylene (PTFE) films were successfully coated with tin oxide in aqueous solutions. Tin oxide was crystallized in the solution and formed nanocrystal coatings on the polymer films. The coatings consisted of SnO₂ and SnO crystals. They were assemblies of tin oxide nanosheet of about 10 to 50 nm in size and about 5 nm in thickness. The nanocrystal films can be exfoliated from the PTFE substrates. Tin oxide nanocrystal films had a rough liquid surface and a dense substrate‐side surface. Transparency of PTFE films coated with tin oxide was same as that of bare PTFE films in the range from 400 to 800 nm. The PTFE films coated with tin oxide nanocrystals can be pasted on desired substrates. Copyright © 2009 John Wiley & Sons, Ltd.