In this paper, a dielectric barrier discharge (DBD) operated at (sub)atmospheric pressure in a 95/5% He/CF₄ mixture is employed to increase the hydrophobicity of a poly(ethylene terephthalate) (PET) film. This paper studies the influence of different operating parameters on the hydrophobic properties of the PET film using contact angle measurements. Results clearly show that the hydrophobicity of the PET film is only enhanced when using large gas flows. Moreover, this work demonstrates that operating pressure and discharge power have a significant influence on the rate of plasma modification as well as on the uniformity of the plasma treatment. Also important to mention is that no ageing effect is observed. As a result, one can conclude that the utilized DBD is an efficient tool to create stable, hydrophobic PET surfaces.

Influence of the unit energy (E_u) of corona discharge used for modification of pure polylactide (PLA) and polylactide nanocomposite (PLAC) containing 5 wt% of an aluminosilicate nanofiller (Cloisite 30B) on water (Θ_W) and diiodomethane (Θ_D) contact angles as well as on surface free energy (γ_s) of these polymers was studied. Θ_W and Θ_D as advancing contact angles were measured with use of a goniometer while γ_s was calculated by the Owens–Wendt method. It was found that Θ_W increased with the rising E_u while Θ_D remained approximately constant. Assuming E_u = const, it could be stated that the increase in γ_s was much more evident for PLA than for PLAC. This increase resulted practically from the change in the polar component of γ_s because the dispersive component for the two materials only slightly decreased with increase in E_u.

Adhesion of epoxy resins on copper foils for printed circuit board (PCB) applications is improved by nearly a factor of 5, using surface cleaning and deposition of a 15-nm-thick film in a low-pressure remote plasma-enhanced chemical vapor deposition process. The cleaning pretreatment, using an N₂–O₂ oxidizing gas mixture with moderate heating (343 K), gives the best results. This pretreatment removes the carbonaceous contaminants present on the topmost surface of the sample and slightly oxidizes the copper into CuO. This oxide is then reduced during the deposition treatment, presumably by reaction with the aminopropyltrimethoxysilane (APTMS) precursor. The surface roughness is unchanged after treatment, thereby showing that the improvement of the copper/epoxy adhesion is only due to the chemistry of the plasma coating. Applying these results to dielectric barrier discharges allows us to achieve the same level of adhesion, which, therefore, does not depend on the process.

Low-pressure plasma generated in a typical parallel plate reactor and atmospheric pressure plasma produced by a plasma needle were utilized to modify the surface of poly(styrene–butadiene–styrene) (SBS) elastomers. An RF discharge (13.56 MHz) in helium was used in the both cases. The SBS surfaces were investigated by T-peel tests, contact-angle measurements, and IRS–FTIR spectroscopy. It has been found that such plasma treatments drastically improve the strength of adhesive-bonded joints between the SBS surfaces and polyurethane adhesives, however, the plasma needle operation has turned out to be more effective. The molecular processes proceeding on the SBS surfaces have been briefly discussed.

An environmentally friendly plasma amination process for the activation of polymers prior to electroless metallization using dielectric barrier discharges (DBD) at atmospheric pressure was investigated. One focus of the work was on the correlation between plasma parameters and palladium coverage on the polymer on the one hand and the palladium coverage and adhesion of a galvanic copper metallization on the other hand. Using XPS spectroscopy it was found that a DBD treatment of polyimide (PI) films with mixtures of N₂ and H₂ leads to considerably higher Pd surface concentrations than on untreated reference samples or foils treated in air-DBD. The Pd coverages achieved result in peel strengths of a copper metallization of up to 1.4 N · mm⁻¹.

World-class, fully automated manufacturing processes rely more and more on advanced, environmentally friendly surface treatment technologies. An innovative atmospheric pressure plasma technique allows inline rubber and plastic manufacturing processes to become fully automated with total process control. A thorough pretreatment must produce surfaces with reliable and repeatable characteristics to achieve optimal adhesive bonding, coating and printing results. In addition, pretreatment must be delivered in a cost-effective and safe manner. The new process uses the high effectiveness of plasma for microfine cleaning, high-surface activation and nanocoating. In most cases the plasma application takes the place of environmentally unfriendly and costly solvent cleaning or chemical adhesion promoters and primers.

A low-temperature, atmospheric pressure oxygen and helium plasma was used to treat the surfaces of polyetheretherketone, polyphenylsulfone, polyethersulfone, and polysulfone. These aromatic polymers were exposed to the afterglow of the plasma, which contained oxygen atoms, and to a lesser extent metastable oxygen (^1δ_g O₂) and ozone. After less than 2.5 seconds treatment, the polymers were converted from a hydrophobic state with a water contact angle of 85±5 to a hydrophilic state with a water contact angle of 13±5 . It was found that plasma activation increased the bond strength to adhesives by as much as 4 times. X-ray photoelectron spectroscopy revealed that between 7% and 27% of the aromatic carbon atoms on the polymer surfaces was oxidized and converted into aldehyde and carboxylic acid groups. Analysis of polyethersulfone by internal reflection infrared spectroscopy showed that a fraction of the aromatic carbon atoms were transformed into C=C double bonds, ketones, and carboxylic acids after plasma exposure. It was concluded that the oxygen atoms generated by the atmospheric pressure plasma insert into the double bonds on the aromatic rings, forming a 3-member epoxy ring, which subsequently undergoes ring opening and oxidation to yield an aldehyde and a carboxylic acid group.

The role of roughening and functionalization processes involved in modifying the wettability of poly(ε-caprolactone) (PCL) after treatment by an atmospheric pressure glow discharge plasma is discussed. The change in the ratio of CO/C–O bonds is a significant factor influencing the wettability of PCL. As the contact angle decreases, the level of CO bonds tends to rise. Surface roughness alterations are the driving force for lasting increases in wettability, while the surface functional species are shorter lived. We can approximate from ageing that the increase in wettability for PCL after plasma treatment is 55–60% due to roughening and 40–45% due to surface functionalization for the plasma device investigated.

A new version of axisymmetric drop shape analysis (ADSA) called ADSA-NA (ADSA-no apex) was developed for measuring interfacial properties for drop configurations without an apex. ADSA-NA facilitates contact angle measurements on drops with a capillary protruding into the drop. Thus a much simpler experimental setup, not involving formation of a complete drop from below through a hole in the test surface, may be used. The contact angles of long-chained alkanes on a commercial fluoropolymer, Teflon AF 1600, were measured using the new method. A new numerical scheme was incorporated into the image processing to improve the location of the contact points of the liquid meniscus with the solid substrate to subpixel resolution. The images acquired in the experiments were also analyzed by a different drop shape technique called theoretical image fitting analysis-axisymmetric interfaces (TIFA-AI). The results were compared with literature values obtained by means of the standard ADSA for sessile drops with the apex. Comparison of the results from ADSA-NA with those from TIFA-AI and ADSA reveals that, with different numerical strategies and experimental setups, contact angles can be measured with an accuracy of less than 0.2°. Contact angles and surface tensions measured from drops with no apex, i.e., by means of ADSA-NA and TIFA-AI, were considerably less scattered than those from complete drops with apex. ADSA-NA was also used to explore sources of improvement in contact angle resolution. It was found that using an accurate value of surface tension as an input enhances the accuracy of contact angle measurements.

The effect of different nebulized liquids directly introduced into the dielectric barrier discharge (DBD) was compared with simple air DBD treatment of polyethylene foils. Water, alcohols and aqueous solutions of different organic substances (environmentally compatible) and water soluble polymers were applied as aerosols and injected into the DBD zone. The DBD residence time (number of treatment cycles) and the power were varied. The durability of the surface modification effect was studied after removing of Low-Molecular Weight Oxidized Material (LMWOM) by washing the samples with water and ethanol. The modified foils were characterized by XPS and contact angle measurements as a function of the applied plasma conditions. The concentration of functional groups at modified surfaces was estimated by derivatization and subsequent XPS measurement.

We present new spreading-drop data obtained over four orders of time and apply our new analysis tool G-Dyna to demonstrate the specific range over which the various models of dynamic wetting would seem to apply for our experimental system. We follow the contact angle and radius dynamics of four liquids on the smooth silica surface of silicon wafers or PET from the first milliseconds to several seconds. Analysis of the images allows us to make several hundred contact angle and droplet radius measurements with great accuracy. The G-Dyna software is then used to fit the data to the relevant theory (hydrodynamic, molecular-kinetic theory, Petrov and De Ruijter combined models, and Shikhmurzaev’s formula). The distributions, correlations, and average values of the free parameters are analyzed and it is shown that for the systems studied even with very good data and a robust fitting procedure, it may be difficult to make reliable claims as to the model which best describes results for a given system. This conclusions also suggests that claims based on smaller data sets and less stringent fitting procedures should be treated with caution.

The surface of high-performance poly(ethylene terephthalate) (PET) fibers is difficult to wet and impossible to chemically bond to different matrices. Sizing applied on the fiber surface usually improves fiber wetting, but prevents good adhesion between a matrix and the fiber surface. The present study demonstrates that the plasma treatment performed by Surface dielectric barrier discharge (Surface DBD) can lead to improved adhesion between sized PET fabric and polyurethane (PU) or poly(vinyl chloride) (PVC) coatings. Moreover, it points out that this plasma treatment can outperform current state-of-the-art adhesion-promoting treatment. Plasma treatment of sized fabric was carried out in various gaseous atmospheres, namely N₂, N₂ + H₂O, N₂ + AAc (acrylic acid) and CO₂. The adhesion was assessed by a peel test, while wettability was evaluated using strike-through time and wicking rate tests. Changes in fiber surface morphology and chemical composition were determined using scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS), respectively. Only the CO₂ plasma treatment resulted in improved adhesion. As indicated by the analyses, increased surface roughness and the incorporation of specific oxygen-containing groups were responsible for enhanced adhesion. The results presented were obtained using a plasma reactor suitable only for batch-wise treatment. As continuous treatment is expected to provide higher homogeneity and, therefore, even better adhesion, a scaled-up Surface DBD plasma system allowing continuous treatment is presented as well.

Polymer and paper structures have been successfully utilized in several fields, especially in the packaging industry. Together with barrier properties, printability is an important property in packaging applications. From the point of view of printing, the dense and impervious structure of extrusion coatings is challenging. Flame, corona and atmospheric plasma treatments were used to modify the surface of low density polyethylene (LDPE) and polypropylene (PP) and the influence of these surface modifications on print quality, i.e., toner adhesion and visual quality was studied. The traditional surface treatment methods, i.e., flame and corona treatments, increased the surface energy by introducing oxygen containing functional groups on the surfaces of LDPE and PP more than helium and argon plasma treatments. Only in the case of flame treatment, the higher surface energy and oxidation level led to better print quality, i.e., toner adhesion and visual quality, than the plasma treatments. The morphological changes observed on LDPE surface after flame treatment are partly responsible for the improved print quality. Atmospheric plasma treatments improved the print quality of LDPE and PP surfaces more than corona treatment. The electret phenomenon observed on LDPE and PP surfaces only after corona treatment is the most likely reason for the high print mottling and low visual quality of corona treated surface.

Using dielectric barrier discharges (DBDs) in suitable gas atmospheres, appreciable densities of amino groups can be generated on polymer surfaces. After the introduction and a few remarks on analytical methods for the determination of functional groups densities, this paper presents a short summary of recent studies on the mechanism of the polymer surface amination from nitrogen and nitrogen/hydrogen mixtures, and possible relevant precursor species. Combination of chemical derivatization with quantitative FT-IR spectroscopy was employed for the determination of primary amino groups densities introduced on polyolefin surfaces in DBD afterglows in N₂ and N₂ + H₂ mixtures. Owing to the possibility to generate atmospheric-pressure plasmas in sub-mm³ volumes, DBD plasmas can be used to modify polymer surfaces area selectively: a new process termed 'plasma printing' can be applied for the achievement of micropatterned surface modifications, such as hydrophilization/hydrophobization or chemical functionalization. Direct-patterning polymer surface modification processes are of interest for biochemical/biomedical applications as well as for polymer electronics. Two examples are presented in more detail: • the area-selective plasma amination of carbon-filled polypropylene minidiscs to manufacture microarrays with peptide libraries utilizing parallel combinatorial chemical synthesis, and •the continuous treatment of polymer foils by means of reel-to-reel patterned plasma amination for the subsequent electroless copper metallization, leading to a fast and highly efficient process for the manufacture of structured metallizations for flexible printed circuits or RFID antennas.

Most polymeric materials, particularly polyolefins and their derivatives, present a low surface energy which is the cause of their poor wettability and limits processes such as adhesive bonding, painting, or metalizing. Many methods have been developed and used to modify polymer surfaces for improved wetting, including mechanical treatments, wet-chemical treatments with strong acids or bases, and exposure to flames or corona discharge. In this paper the improvement of wetting properties of several polymeric materials widely used in the automotive industry, such as high density polyethylene (HDPE), low density polyethylene (LDPE), polypropylene (PP) and silicone, is studied by means of surface mechanical abrasion using sandpapers of different grain sizes (1000, 180 and 80). Measurements of the surface roughness are performed using a Hommel Tester T8000 device equipped with a diamond stylus, which provides data on the arithmetic average roughness R_a parameter and Abbott–Firestone curve. Variations in the polymers surface energy (SE) are estimated through contact angle measurements using five test liquids of different polarities. Both components of the SE, dispersion (σ^D) and polar (σ^P), as well as total (σ^T) at different conditions of treatment are analyzed using the Owens–Wendt–Rabel–Kaelble (OWRK) method. Morphological changes induced in the surface are analyzed by Scanning Electron Microscopy (SEM). Additionally, measurements of the static friction coefficient (μ_s) are carried out by the standard method ASTM D 1894-08. A slight enhancement in surface wettability is found with the mechanical abrasion pre-treatment from the SE increase. Finally, a higher value of μ_s is achieved for the abraded specimens as the normal force acting onto the system is increased.

In this work a DC plasma reactor was used for deposition of plasma polymerized coating from hexamethyldisiloxane-Ar (35/65%) mixture on polypropylene films. Surface energy parameter have been calculated using Owens-Wendt approaches with the sessile drop method are used to obtain the dispersive γ^D and polar γ^P component of surface free energy. The surface morphology of samples were investigated using scanning electron microscope. Also the chemical properties and wetability of prepared samples were tested using Fourier transform infrared spectroscopy and contact angle measurement, respectively.

Polyethylene terephthalate (PET) plates have been exposed to different nitrogen containing plasmas with the purpose of incorporating nitrogen functional groups on its surface. Results with a dielectric barrier discharge (DBD) at atmospheric pressure and a microwave discharge (MW) at reduced pressure and those using an atom source working under ultrahigh vacuum conditions have been compared for N₂ and mixtures Ar + NH₃ as plasma gases. The functional groups have been monitored by X-ray Photoemission Spectroscopy (XPS). Nondestructive oxygen and carbon depth profiles for the plasma treated and one month aged samples have been determined by means of the nondestructive Tougaard’s method of XPS background analysis. The surface topography of the treated samples has been examined by Atomic Force Microscopy (AFM), while the surface tension has been determined by measuring the static contact angles of water and iodomethane. It has been found that the DBD with a mixture of Ar+NH₃ is the most efficient treatment for nitrogen and amine group functionalization as determined by derivatization by reaction with chlorobenzaldehyde. It is also realized that the nitrogen functional groups do not contribute significantly to the observed increase in surface tension of plasma treated PET.

In this work the influence of the atmospheric pressure plasma treatment on the surface properties of polypropylene (PP) films was investigated. The film samples were modified by atmospheric pressure plasma treatment by diffuse coplanar surface barrier discharge (DCSBD) using ambient air as working gas. The contact angle measurement, the test pen method, atomic force microscopy (AFM) and attenuated total reflection technique Fourier transformed infrared spectroscopy (ATR-FTIR) were applied to analyze the changes of the surface of the polymer film. In all experiments, the contact angle of the treated polypropylene samples decreased and the surface energy of the samples increased in comparison with the plasma untreated samples. The proper surface energy for printing using solvent-based inks was detected by all the samples. There were not observed any significant changes in mechanical properties of the films after plasma treatment by measuring their tear parameters.

The objective of this paper was to understand the effects of plasma activation, and thus influence of the surface energy and chemistry changes on offset print quality. Pigment coated and surface sized papers were treated with corona and atmospheric plasma in pilot and laboratory scales. The surface energy and surface chemistry changes were evaluated by contact angle and X-ray photoelectron spectroscopy (XPS). Offset printing was performed in laboratory scale with an IGT unit with predampening and in a pilot scale sheet-fed offset printing press. In addition, the ink setting rate was measured using an ink on paper tack tester. Plasma activation increased the surface energy of the papers. Furthermore, the polarity of the paper surface increased due to formed polar oxygen containing molecular groups. Due to differences in treatment times laboratory scale plasma treatment formed mainly carboxyl and ester groups, whereas pilot scale treatment induced mainly alcohol, ethers, aldehydes and/or ketones on paper surfaces. Printing evaluation showed that plasma activation influences both ink and water absorption properties. According to print tack results plasma activation led to faster ink-setting. With hydrophobic surface-sized paper plasma activation influenced the ink transfer, print gloss and density by changing dampening water absorption properties. The difference in surface chemistry with laboratory scale plasma treated samples was also reflected in the print quality properties. SEM imaging showed that too intense plasma

One of the parameters characterizing the surfaces of materials is the surface free energy. The most common way to determine its value is to measure the surface tension by the sessile drop method. In this case a contact angle between the surface and the edge of droplets of liquids is measured. There are various approaches to calculate the surface free energy from the contact angle measurements. We made a review and a direct comparison of the most widely used methods and testing liquids in order to re-evaluate their advantages and disadvantages. In the presented work we discuss the limits of applicability of the examined methods. We confirm that methods using a pair of liquids give results dependent on the liquids chosen. Using a pair of non-polar and polar liquid yielded most reliable results. This is even more clear when two-liquid method is transformed into a multiple-liquid method. The algorithms developed during the work will be implemented into liquid contact angle analysis software.

Four types of contact angles (receding, most stable, advancing, and “static”) were measured by two independent laboratories for a large number of solid surfaces, spanning a large range of surface tensions. It is shown that the most stable contact angle, which is theoretically required for calculating the Young contact angle, is a practical, useful tool for wettability characterization of solid surfaces. In addition, it is shown that the experimentally measured most stable contact angle may not always be approximated by an average angle calculated from the advancing and receding contact angles. The “static"” CA is shown in many cases to be very different from the most stable one. The measured contact angles were used for calculating the surface tensions of the solid samples by five methods. Meaningful differences exist among the surface tensions calculated using four previously known methods (Owens-Wendt, Wu, acid-base, and equation of state). A recently developed, Gibbsian-based correlation between interfacial tensions and individual surface tensions was used to calculate the surface tensions of the solid surfaces from the most stable contact angle of water. This calculation yielded in most cases higher values than calculated with the other four methods. On the basis of some low surface energy samples, the higher values appear to be justified.

There are many current and emerging wetting and adhesion issues which require an additional surface processing to enhance interfacial surface properties. Materials which are non-polar, such as polymers, have low surface energy and therefore typically require surface treatment to promote wetting of inks and coating. One way of increasing surface energy and reactivity is to bombard a polymer surface with atmospheric plasma. When the ionized gas is discharged on the polymer, effects of ablation, crosslinking and activation are produced on its surface. In this paper we will analyse the role of plasma and its use in increasing the surface energy to achieve wettability and improve adhesion of polymeric surfaces.

Blown film processors, large and small, have limited resources in both capital and manpower to devote to optimizing their productivity. Yet avenues of improvement are open for even the most over-extended organization. And some of the most effective modifications cost little more than a small change in equipment orientation or procedures. A key aspect of optimizing a blown film layout is line footprint and determining how to minimize footprint and maximize output with each integral piece of equipment on the line. Multiple surface treatment systems are integral to every blown film line and can control product quality and line efficiencies. The objective of this work is to present best practices of blown film manufacturers ranging from multinationals to small privately owned operations relative to the most effective surface treatment system designs, their roll coverings, optimum power density settings, alternative treatment technologies, troubleshooting protocols, and model line layouts that optimize production output.

An atmospheric pressure oxygen and helium plasma was used to activate the surface of poly(methyl methacrylate) (PMMA). The plasma physics and chemistry was investigated by numerical modeling. It was shown that as the electron density of the plasma increased from 3 × 10¹⁰ to 1 × 10¹² cm⁻³, the concentration of O atoms and metastable oxygen molecules (¹Δ_g) in the afterglow increased from 6 × 10¹⁵ to 1 × 10¹⁷ cm⁻³. Exposing PMMA to the afterglow for times between 0 and 30 s led to a 35° ± 3° decrease in water contact angle, and a ten-fold increase in bond strength to several adhesives. X-ray photoelectron spectroscopy of the polymer revealed that after treatment, the surface carbon attributable to the methyl pendant groups decreased 5%, while that due to carboxyl acid groups increased 7%. The numerical modeling of the afterglow and experimental results indicate that oxygen atoms generated in the plasma oxidize the polymer chains.

In this work, an experimental investigation of fluorine gas (F₂) plasma treatment of polypropylene (PP) film reveals the evolution of PP fluorination. Surface analysis of fluorinated PP surfaces describes a surface modification process that is initially quite rapid but slows sharply as the fluorination progresses. The fluorination reaction occurs more rapidly at the PP film surface and evidence of a treatment gradient is seen in the ESCA sampling depth of 10 nm. The increasingly fluorinated surface becomes less reactive to the plasma chemistry and develops a fully fluorinated, cross-linked surface layer that eventually extends the full ESCA sampling depth.

A theory, based on the presence of an adsorbed film in the vicinity of the triple contact line, provides a molecular interpretation of intrinsic hysteresis during the measurement of static contact angles. Static contact angles are measured by placing a sessile drop on top of a flat solid surface. If the solid surface has not been previously in contact with a vapor phase saturated with the molecules of the liquid phase, the solid surface is free of adsorbed liquid molecules. In the absence of an adsorbed film, molecular forces configure an advancing contact angle larger than the static contact angle. After some time, due to an evaporation/adsorption process, the interface of the drop coexists with an adsorbed film of liquid molecules as part of the equilibrium configuration, denoted as the static contact angle. This equilibrium configuration is metastable because the droplet has a larger vapor pressure than the surrounding flat film. As the drop evaporates, the vapor/liquid interface contracts and the apparent contact line moves towards the center of the drop. During this process, the film left behind is thicker than the adsorbed film and molecular attraction results in a receding contact angle, smaller than the equilibrium contact angle.

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.