We present a study on ageing of polymethyl methacrylate (PMMA) polymer treated with oxygen plasma. Oxygen plasma was created with an RF generator operating at a frequency of 27.12 MHz and a power of 200 W. The oxygen pressure was 75 Pa. The samples were treated for different time from 5 s to 60 s. The chemical modifications of the surface after plasma treatment were monitored by XPS (X-ray photoelectron spectroscopy), while the wettability and ageing effects were studied by WCA (water contact angle measurements). The samples were aged in dry air or in water. In the case of dry air, the least pronounced ageing was observed for the sample treated for 60 s. For samples aged in water, however, the lowest ageing rate was observed for the sample treated for 5 s. The samples were ageing slightly faster in water than in air. We also investigated the temperature effect on ageing of plasma treated samples. A set of samples was stored in a refrigerator at 5 °C and the other set was placed into an oven at 50 °C. The ageing rate of the samples stored at 5 °C was significantly lower than for the samples stored at 50 °C, so cooling the samples help keeping the required surface properties.An atmospheric pressure plasma syste

Several techniques have been applied for the characterization of three PET films surfaces: homopolymer PET film, corona treated PET film and a poly(ethylene terephthalate‐co‐1,4‐cyclohexanedimethanol) film. The objective of this work is to investigate and to apply precise and mutually complementary techniques which give detailled information about theses surfaces, as there are few papers with global and conclusive results. The film surfaces were investigated to support the development of new products and envisage new apllications to the existent films. Scanning electron micrographs, attenuated total reflection Fourier transform infrared spectroscopy (FTIR‐ATR) and multiple internal reflection Fourier transform infrared spectroscopy (FTIR‐MIR) spectra show that the chemical composition, topography and surface roughness of the films are different. The corona‐treated PET film shows high surface tension value due to the major contribution on the polar groups and oxidation level acquired. The copolyester film is much less crystalline than the other films analyzed, as demonstrated by refractive index measurements and X‐ray photoelectron spectroscopy (XPS). The amorphous structures obtained and the high tension level of the corona‐treated films provide a better understanding of the adhesion phenomena. In view of results obtained, one can assume that corona treated films owing to its higher surface tension and films with CHDM owing to its surface amorphization should provide manufacturing industries better processing conditions than films without surface treatment and also higher levels of adhesion to paints and coatings.

The invention relates to equipment for area-based surface treatment of an article by electric dielectric barrier discharge in the presence of a non-atmospheric controlled gaseous mixture, comprising a hollow metal electrode enabling the gaseous mixture to circulate therewithin and the mixture to be transported to a discharge area, whereby said electrode is divided into individual elements which can each be pivoted about a central axis to ensure sufficient distance between the element which is considered as being pivoted and the area of the article opposite the element in question so that the discharge cannot develop; the central pivoting axis is used as a channel for the circulation of the gaseous mixture inside the electrode and is provided with openings enabling the gaseous mixture to be evacuated to the discharge area; pivoting one of the elements of the electrodes blocks up the evacuating opening associated therewith and the gaseous mixture can only be evacuated via the evacuating openings of non-pivoted elements.

Based on the Corona process and a substitution of air with specific gaseous mixtures into the discharge area, the newly developed surface treatment ALDYNE™ offers both high level improvement and high flexibility to film converters. By grafting nitrogen-based chemical functions, it confers to the treated surface excellent properties such as high surface energy and high adhesion of coatings.

Nylon 6 electrospun nanofibers were deposited on plasma-pretreated woven fabric substrates with the objective of improving adhesion between them. The prepared samples were evaluated for adhesion strength and durability of nanofiber mats by carrying out peel strength, flex resistance, and abrasion resistance tests. The test results showed significant improvement in the adhesion of nanofiber mats on woven fabric substrates due to atmospheric plasma pretreatment. The samples also exhibited good flex and abrasion resistance characteristics. X-ray photoelectron spectroscopy and water contact angle analyses indicate that plasma pretreatment introduces radicals, increases the oxygen content on the substrate surface, and leads to formation of active chemical sites that may be responsible for enhanced cross-linking between the substrate fabric and the electrospun nanofibers, which in turn increases the adhesion properties. The work demonstrates that the plasma treatment of the substrate fabric prior to deposition of electrospun nanofiber mats is a promising method to prepare durable functional materials.

In this work, the effect of the surface modification of polypropylene films via corona treatment was investigated. Polypropylene films were treated with negative and positive corona discharge, at atmospheric pressure, for 5 minutes, at two different temperatures – 25 °C and 90 °C. The changes in the surface free energy were investigated by means of contact angle measurements. The Bickerman's method was applied to determine the polar and dispersion components of the polymer surface free energy, on the basis of the theory of Owens, Wendt, Kaelble and Uy. Atomic force microscopy was used to analyze the polymer surface morphology changes of the films with temperature. According to the findings, in all cases the corona treatment increases the surface free energy of polypropylene films and its polar part, in comparison with the untreated samples. The effects of negative and positive corona polarities display some specific features which could be associated with different charged group introduced onto the film surface during the corona treatment. The total final effect depends on the simultaneous action of the two competing factors – temperature and corona polarity. The most pronounced effect was observed for high temperature negative corona treatment.

Ni, Fe, Ti, Al, Au, and Cu were each evaporated and deposited onto both sides of polyethylene and poly(tetrafluoroethylene) (PTFE) films. Adhesive joint strengths of the different metal–polymer–metal composites were compared and subsequent surface modifications due to metalization were investigated. Studies show no change in wettability of polyethylene or PTFE after a metal layer was deposited onto their surfaces and subsequently removed. There was also no evidence of oxidation or unsaturation of the surface. Gel fractions of polyethylene show a definite correlation between joint strength and crosslink at the surfaces of the different metal–polymer composites. Metals forming the strongest joints with polyethylene yield the greatest amount of crosslinking. Conversely, metals forming the weakest joints result in the least amount of crosslinking.

It is now generally recognized that the principal forces contributing to the work of adhesion between two phases, W_A, are the Lifshitz-van der Waals forces (which include a small contribution from permanent and induced dipoles) and acid-base interactions, taken in the most general 'Lewis' sense. One may thus write W_A = W^LW_A + w^ab_A = 2√σ^LWSσ^LWL + fN(-ΔH^ab), where W^LW_A and W^ab_A are the Lifshitz-van der Waals and acid-base contributions to the work of adhesion, and σ^LW_S and σ^LW_L are the Lifshitz-van der Waals contributions to the surface free energies of the solid and the liquid, respectively; ΔH^ab is the enthalpy (per mol) of the acid-base adduct formation between the acid or base functional groups on the adherend and in the adhesive; N is the number (moles) of accessible functional groups per unit area of the adherend; and f is an enthalpy-to-free energy correction factor (which has normally been assumed to be ~1). The present work seeks to evaluate W^ab_A for several systems using wetting measurements and, for at least one system, to obtain a quantitative check of the above equation using independently measured values of f, N, and (ΔH^ab). The total work of adhesion is determined from the measured surface tension of the liquid, σ_L' and its contact angle, 0, against the solid: W_A= σ_L(1 + cos ). σ^LW_S and σ^LW_L are determined using probe liquids, N is determined from conductometric titrations of the solid in finely divided form, and ΔH^ab is determined by flow microcalorimetry. f is determined from a Gibbs-Helmholtz analysis of surface tension and contact angle data obtained over a range of temperatures. Conclusions reached are that the f factor is significantly below unity in most cases and that even including this effect, the above equation is still not verified quantitatively when the terms are measured independently.

The surface modification and adhesive bonding of a unidirectional GFRP Nylon-6,6 thermoplastic composite has been investigated. Wettability studies of plasma-treated specimens showed a significant reduction in the advancing and receding contact angles in water, relative to untreated material. The most effective treatment used oxygen plasma. The increases in wettability observed were determined to be the result of (a) an increase in the concentration of oxygen- and nitrogen-containing functional groups on the surface of the polymer and, (b) removal of fluoropolymer contamination, the source of which was identified as the PTFE mould release agent. This was established by SSIMS analysis. The surface modification resulted in significantly improved adhesion between the composite and an applied toughened epoxy adhesive; a considerable increase in the Mode II critical strain energy release rate, G_IIc, was observed following plasma treatment. Specimens treated in an oxygen plasma showed the greatest improvement in G_IIc, failing cohesively at a value of 1.6 kJ·m⁻² after only 15 seconds exposure. Without plasma treatment the specimens failed in an adhesive mode at very low values of G_IIc. Adhesion was further optimised by moulding the GFRP Nylon-6,6 against steel plates instead of PTFE.

A web or film is electrostatically charged by sequentially subjecting the web or film to a series of electric fields such that adjacent electric fields have substantially opposite polarities. Both a method and apparatus are disclosed for charging the web or film.

The wetting of cylindrical monofilaments by liquid polymers is a problem of much scientific and technological importance. In particular, the characterization of the physicochemical nature of interfaces is a key problem in the field of advanced fibrous composites. The macroscopic regime contact angle, which reflects the energetics of wetting at the solid-liquid interface, is difficult to measure by usual methods in the case of very thin cylindrical fibers.

In the present article a numerical method is proposed for the calculation of macroscopic regime contact angles from the shape of a liquid droplet spread onto a cylindrical monofilament. This method, which builds on earlier theoretical treatments by Yamaki and Katayama [1], and Carroll [2], very much improve the accuracy of the contact angle obtained. Experimental results with high-strength carbon, para-aramid, and glass fibers, are presented to demonstrate the high degree of accuracy of the method proposed.

Barrier discharges (BDs) produce highly non-equilibrium plasmas in a controllable way at atmospheric pressure, and at moderate gas temperature. They provide the effective generation of atoms, radicals and excited species by energetic electrons. In the case of operation in noble gases (or noble gas/halogen gas mixtures), they are sources of an intensive UV and VUV excimer radiation. There are two different modes of BDs. Generally they are operated in the filamentary one. Under special conditions, a diffuse mode can be generated. Their physical properties are discussed, and the main electric parameters, necessary for the controlled BD operation, are listed. Recent results on spatially and temporally resolved spectroscopic investigations by cross-correlation technique are presented. BDs are applied for a long time in the wide field of plasma treatment and layer deposition. An overview on these applications is given. Selected representative examples are outlined in more detail. In particular, the surface treatment by filamentary and diffuse BDs, and the VUV catalyzed deposition of metallic layers are discussed. BDs have a great flexibility with respect to their geometrical shape, working gas mixture and operation parameters. Generally, the scaling-up to large dimensions is of no problem. The possibility to treat or coat surfaces at low gas temperature and pressures close to atmospheric once is an important advantage for their application.

Modified surfaces of polyethylene terephthalate)(Mylar® or PET film) have been studied by surface energetics, ESCA, atomic force microscopy (AFM), and optical profilometry. For the surface energetics studies, receding contact angle titrations were used to evaluate the surface functional groups in the outer few angstroms of the surface. This sensitive method of determining the contact angle with buffer solutions of different pHs allows one to investigate the nature of the chemical species introduced by the various energetic treatments. The data are consistent with a surface that is covered by a low density of carboxylic acid moieties in the case of corona and flame treatments, applied in a high-speed commercial type of a process at low doses. The high contact angle hysteresis indicates that the coverage is moderately heterogeneous but on a very small length scale, less than a few micrometers. ESCA qualitatively supported this, although this technique is not optimum for the low degrees of surface modification. A comparison is made of the two surface treatments in terms of depth of penetration, roughness, and surface density of chemical moieties introduced. UV laser-treated surfaces showed no indication of surface chemical modification.

The effects of exposure to ultraviolet (UV) light and ozone, separately and in combination, were investigated with respect to polypropylene (PP) and poly(ethylene terephthalate) (PET) surfaces. Three combinations of UV light and ozone were studied: ozone only, UV light in air (producing ozone), and UV light in air (producing ozone) supplemented by additional ozone in the incoming air. The effect of the exposure time of the PP and PET to each treatment was studied. The samples were analyzed by X-ray photoelectron spectroscopy (XPS) to determine the surface composition, and by dynamic contact angle to determine the water wettability. The results showed that the effect of the treament was dependent on the properties of the exposed polymer, with PET being more sensitive to the UV light and PP being more sensitive to the reactive species in the gas. The exposure times studied ranged from 1 to 90 min. By monitoring the oxygen uptake levels, we were able to determine that surface modification occurred within minutes. The possible reactive species and mechanisms are discussed.

o optimize the effects of some discharge parameters on the surface wettability of polypropylene (PP) in atmospheric pressure dielectric barrier discharge, a surface modification model is created based on statistical theory and orthogonal experimental design method. Contact angle measurements, atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) are used to study the changes in the surface wettability, surface topology and chemical compositions of the samples. The results show that surface wettability has been improved due to roughness increasing and the introduction of oxygen-containing functional groups. High-resolution XPS of C1s peak deconvolution indicates that the types and contents of oxidized functional groups are different in different discharge conditions or plasma energy. Moreover, the model analysis reveals that it has better predictive ability, and different discharge parameters has selective influence on water contact angle and surface O atom percentage.

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.

The aging effects of atmospheric pressure plasma treated fiber surfaces are important for storage and processing of the fibers. One of the high-performance fibers, ultrahigh modulus polyethylene (UHMPE) fiber, was chosen as a model system to investigate the aging process of atmospheric pressure plasma jet (APPJ) treated fibers surfaces 0, 7, 15 and 30 days after initial plasma treatment. The fiber was first plasma-treated and then stored at temperatures varying from −80 to 80°C on the same relative humidity (RH, 0%) and on RH of 0%, 65% and 100% at the same temperature of 20°C. Immediately after the plasma treatment, scanning electron microscope (SEM) showed the roughened fiber surface. X-ray photoelectron spectroscopy analysis showed changed surface chemical compositions. Contact-angle measurement showed increased surface wettability and microbond test showed an increase in IFSS. With increasing relative humidity or decreasing temperature, the IFSS value decreased and the contact angle increased more slowly. However, after 30 days, the IFSS values and contact angles reached a similar level for all groups. Moisture showed no effect on the single fiber tensile strengths during aging. The reasons for the observed aging behavior could be that decreasing temperature or increasing relative humidity hindered the surface rearrangement of polymer chains after plasma treatment.

In this paper, a dielectric barrier discharge operating in nitrogen at atmospheric pressure has been used to improve the surface hydrophilic property of polypropylene (PP) non-woven fabric. The changes in the hydrophilic property of the modified PP samples are investigated by the contact angle measurements and the variation of water contact angle is obtained as a function of the energy density; micrographs of the PP before and after plasma treatment are observed by scanning electron microscopy (SEM) and the chemical composition of the PP surface before and after plasma treatment is also analyzed by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The results show that the surface hydrophilic property of the PP samples is greatly improved with plasma treatment for a few seconds, as evidenced by the fact that the contact angle of the treated PP samples significantly decreases after plasma treatment. The analysis of SEM shows that the surface roughness of the treated PP samples increases due to bonding and etching in plasma processing. The analyses of FTIR and the C1s peak in the high-resolution XPS indicate that oxygen-containing and nitrogen-containing polar functional groups are introduced into PP surface in plasma processing. It can be concluded that the surface hydrophilic property of the modified PP samples has been obviously improved due to the introduction of oxygen-containing and nitrogen-containing polar groups and the increase of the surface roughness on the PP surface.

The surface contact angle of glycerol and of water on polystyrene (PS) films has been found to depend on the extent of uniaxial draw for atactic PS. The contact angle depends on direction for the smooth films of PS drawn by solid state coextrusion. Results as a function of draw ratio to values over 4 on these noncrystalline PS samples, M_w = 6 × 10⁵, have also been interrelated with other measures of orientation such as the anisotropy of surface and bulk properties measured, respectively, by dichroic reflectance infrared spectroscopy and by birefringence.

Polystyrene, a polymer extensively used in the biomedical field, causes a problem for some applications because of its surface hydrophobicity. Nitrogen plasma could transform this shortage through polar group attachment. To understand the role of hydrogen during surface functionalization in the nitrogen cold plasma, the effects of the nitrogen and the mixture of N₂/H₂ plasma are investigated by both the examinations of the densities of attached amine groups and the in-situ diagnostic analyses such as optical emission spectroscopy and mass spectrometry. An increase of functionalization has been proved to be controlled by the gaseous NH radical formation when H₂ is added.

The choice of plasma gas can determine the interaction between material and plasma and therefore the applications of the treated materials. Nitrogen plasma can integrate functional groups such as primary amines and carbon dioxide plasma can incorporate carboxylic groups on the surface of polymers. For specific adhesion such as bio-adhesion, polar groups must be attached to the surface to enhance bio-film formation but the acidic or basic character also controls the adhesion mechanism.

Nitrogen and carbon dioxide plasmas are chosen to treat the surface of polystyrene and to show the effects of different functionalizations, i.e. attachment of acid or basic groups and degradation are compared in the present work.

Nitrogen-containing plasma induces mainly weak degradation at a rate of ∼0.13 µg cm⁻²s⁻¹. The roughness of the treated surface remains mostly unchanged. Functionalization leads to amino group attachment at a concentration of 1.2 sites nm⁻². We found that carbon dioxide plasma treatment shows more drastic degradation with a rate three times higher than that of nitrogen plasma and can create more functional groups (4.5 sites nm⁻²) at mild plasma treatment. However, the roughness of the surface is altered. In both cases the aromatic groups are degraded through the plasma treatment (again this is more evident with the CO₂ plasma) and the induced functionalization was shown to be quick (the upper monolayer of polystyrene film can be functionalized rapidly). Copyright © 2005 John Wiley & Sons, Ltd.
https://analyticalsciencejournals.onlinelibrary.wiley.com/doi/abs/10.1002/sia.2029

Using Gibbs’ method of dividing surfaces, the contact angle of a drop on a flat homogeneous rough non-deformable solid substrate is investigated. For this system, a new generalized Young’s equation for the contact angle, including the influences of line tension and which valid for any dividing surface between liquid phase and vapor phase is derived. Under some assumptions, this generalized Young’s equation reduces to the Wenzel’s equation or Rosanov’s equation valid for the surface of tension.

The adhesion strength of a perfluorinated dielectric adhesive to polyphenylene sulfide (PPS) was investigated. The effect of different fillers in the PPS as a function of plasma treatment conditions was evaluated. The change in adhesion as a result of thermal baking was also addressed. The surface composition and surface energy were monitored and systematically quantified by X-ray Photoelectron Spectroscopy (XPS) and contact angle measurements, respectively. The correlations between the presence of certain functional groups, change in surface energy and polarity, and variation in adhesion properties indicate that the adhesion mechanism is mainly due to van der Waals forces. Enhanced wetting at the adhesive/substrate interface and a deeper interfacial diffusion zone are found to be necessary conditions to achieve the optimal adhesion.

A liquid to solid material surface contact angle measurement system operating by way of detecting a transition in the behavior of a liquid sample with the solid material in a changing angular confinement environment along with use of a mathematical algorithm to then determine contact angle. Measurement of the angle at which the tested liquid transitions between apparent wetting and apparent non-wetting behavior, regardless of whether the liquid and solid material are truly classified as wetting or non-wetting, provides a measurement from which disclosed mathematical algorithms can predict the surface wetting characteristics of the liquid on the solid material. Automated performance of the confinement environment measurement and examples are included.

Cotton fibers from four varieties were washed with water using two procedures that included several combinations of temperatures and water volumes. Wettability of unwashed and washed fibers was determined by contact angle measurement and by a sink-float technique. The sink-float technique could be used to sort washed and unwashed cotton fibers.

Penetration of Liquids into Cylindrical Capillaries.—The rate of penetration into a small capillary of radius r is shown to be: dl dt= P (r 2+ 4 ε r) 8 η l, where P is the driving pressure, ε the coefficient of slip and η the viscosity. By integrating this expression, the distance penetrated by a liquid flowing under capillary pressure alone into a horizontal capillary or one with small internal surface is found to be the square root of (γ rt· cos θ 2 η), where γ is the surface tension and θ the angle of contact. The quantity (γ cos θ 2 η) is called the coefficient of penetrance or the penetrativity of the liquid.