Three polyethylene (PE) types with different branching structures were subjected to air, water and ethanol aerosol-assisted dielectric barrier discharges (DBD) for surface modification. Using the air DBD the incorporated oxygen concentration was found to be independent on the branching of PE in contrast to the introduction of OH groups, which was PE-2 > PE-1 > PE-3. For water-aerosol DBD the succession of OH concentration was in the order of PE-1 > PE-2 > PE-3. Ethanol aerosol-assisted DBD produced the lowest concentration of OH groups also independent on the branching of PE. The chemical nature of introduced oxygen functional groups was inspected by X-ray photoelectron spectroscopy (XPS) and assigned as CO, >CO/CHO/OCO and OCO.

Static contact angle and dynamic (advancing and receding) contact angles of water on polymeric surfaces were investigated using microscope cover glasses coated with various plasma polymers of trimethylsilane and oxygen. By variation of the mole fraction of the TMS/oxygen mixture, glass surfaces having varying degrees of wettability were prepared. The advancing contact angle of a sessile droplet, which is independent of the droplet volume, is considered as the static contact angle of water on a polymeric surface, θ_S, which is a parameter characteristic to a polymeric surface. The dynamic contact angle of water refers to the contact angle of which three-phase contact line is in motion with respect to the surface. The dynamic advancing (immersing) contact angle, θ_D,a, and receding (emerging) contact angle, θ_D,r, were measured by the Wilhelmy balance. The difference between θ_D,a and θ_D,r is mainly due to the direction of dynamic force acting on the three-phase contact line. The discrepancy between the immersion and the emersion buoyancy lines and the corresponding values of contact angles can be used to indicate the hysteresis due to the dynamic factor (the dynamic hysteresis). The dynamic hysteresis is largely determined by the critical immersion depth in which the three-phase contact line remains at the same place on the surface while the shape of meniscus changes when the motion of the sample is reversed. The dynamic hysteresis may contain the contribution of the change of static contact angle due to the surface-configuration change caused by the wetting of the surface (the intrinsic hysteresis). The dynamic hysteresis varies according to the value of cos θ_S, with the maximum at the threshold value around 0.6 and linearly decreases above this value, as the emersion line approaches the limiting buoyancy line determined by the surface tension of the liquid. The intrinsic hysteresis follows the same trend with the maximum at around 0.8. The three contact angles are related by cos θ_S = (cos θ_D,a + cos θ_D,r)/2.

In the gas flame treatment of low surface free energy (SE) substrates, such as high-density polyethylene (HDPE), problems might arise from under or over flaming, oxygen concentration differences in and around of the flame, etc. Consequently, in printing applications, the possible variation of induced SE existing on the surface, could cause distortion on printed letters. In this research, a new method based on the wetting and spreading phenomena was developed to display and study details of the SE variation on HDPE flame treated substrates. It was an easy and quick method. Results showed good agreements with previous works done on the flame treatment characteristics. The optimal flaming was achieved, while the substrate surface had been positioned about 10 to 12 mm below the tip of the flame's blue part. Also when the flaming speed had been controlled about 80 mm/s. Results from the adhesion strength test supported the optimum situations found previously by others. It was hoped that this new method could also be capable of estimating the critical SE of solid surfaces in future works.

Currents during corona charging and surface potential decay after corona charging have been studied on polymeric films. As has been reported before, surface potential is a useful tool for investigating the electrical properties of an insulating material, making it possible to discriminate charge injection from polarization processes, when data are correctly analysed, and it has also been shown that, on thin polymeric films, slow polarization processes leading to heterocharge formation dominate at low fields, while charge injection occurs above a given field threshold. We present here a combined study of the surface potential after charge deposit and current flowing on the back electrode during the corona charge; we show that current measurements during the charge confirm the interpretation of potential measurements after corona charge. The outbreak of “hollows” in the potential distribution on the surface is clearly linked to the predominance of injected charge on the polarization charge. However, even at high fields, polarization phenomena will dominate again a given time after corona discharge stopping.

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.

The effects of oxygen-plasma treatment of ultra-high-modulus polyethylene (UHMPE) fiber on the transverse properties of the UHMPE fiber/vinylester composites have been investigated. The UHMPE fiber/vinylester unidirectional (UD) laminates were prepared with untreated and oxygen-plasma-treated UHMPE fiber. The oxygen-plasma treatment of the UHMPE fiber increases the transverse tensile strength and failure strain of UHMPE-fiber/vinylester composites and changes the failure initiation site from the interface to the interior of the UHMPE fiber. The oxygen-plasma treatment of the UHMPE fiber introduced micro-pits on the fiber surface; these micro-pits improve the interfacial adhesion in UHMPE fiber/vinylester composites through the mechanical interlocking between the micro-pits and the vinylester resin. Finite-element (FE) modeling was performed to investigate the effect of the micro-pits on stress transfer in the UHMPE-fiber/vinylester composite. The micro-pits are known to increase the stress transfer from the vinylester resin to the UHMPE fiber and this increased stress transfer is correlated with the improved transverse properties and the transition of the failure initiation site after oxygen plasma treatment.

The interfacial adhesion of ultrahigh-modulus polyethylene (UHMPE) fibre–vinylester composites was improved by the oxygen plasma treatment of the UHMPE fibre. The chemical functional group formations on the UHMPE fibre surface by oxygen plasma treatment were analysed using diffuse reflectance Fourier transform infrared spectroscopy and the morphological changes of the UHMPE fibre surface by plasma etching were observed by scanning electron microscopy. The wettability enhancement by the chemical functional group formation and the mechanical interlocking due to the micropits were important factors in improving the interfacial adhesion of the UHMPE fibre–vinylester composites by oxygen plasma treatment. In order to investigate the relative importance of the two factors, wettability enhancement and mechanical interlocking, in the improved interfacial adhesion of the UHMPE fibre–vinylester composites, nitrogen plasma treatment was also performed. Nitrogen plasma treatment of the UHMPE fibre was proved to be effective in the formation of the micropittings and ineffective in the chemical functional group formation in comparison with the oxygen plasma treatment. The interlaminar shear strengths of the nitrogen-plasma-treated UHMPE fibre–vinylester composites showed almost the same value as those of the oxygen-plasma-treated UHMPE fibre–vinylester composites. The wettability enhancement and mechanical interlocking are important in the improvement of interfacial adhesion of UHMPE fibre–vinylester composites by plasma treatment and mechanical interlocking seems to be more important.

Oxidative activation of resinous wood surfaces by a corona treatment to improve adhesive bonding was studied. It was found that the wettability of the veneers, including hardwoods, softwoods, and tropical woods increased with an increase in the degree of treatment, and the gluability increased rapidly after the initial mild treatment. To elucidate the nature of any chemical change occurring on the wood surface, the dyeing examination of the wood and its components with Schiff's reagent was made, and the results showed a higher dyeing ability for corona-treated samples compared to untreated ones, indicating that aldehyde groups increased by the corona treatment. The treatment affected the alcohol-benzene extractives, and oxidized them to produce aldehyde groups. Especially, the neutral fraction in the extractives was significantly affected. On the other hand, negligible chemical effects of the treatment on the surface modification of the wood's main components were seen. Both the untreated and corona-treated samples adsorbed basic dye to the same extent of coloration. Thus, no measurable carboxyl groups increased on the surface of the samples. It seems that an increase in the wettability of corona-treated wood veneers resulted mainly from the oxidation of the high hydrophobic surface layer of neutral fraction substances in the extractives, and from the reduction in their hydrophobicity. © 1993 John Wiley & Sons, Inc.
https://onlinelibrary.wiley.com/doi/abs/10.1002/app.1993.070490714

Polyethylene (PE) and polypropylene (PP) were oxygen plasma treated and aged in carefully reproducible conditions. The effect of aging on the surface chemistry, wettability and adhesion were studied using a combination of techniques: contact angle measurements, XPS, SSIMS, adhesion tests (shear and pull).

PE was found to be relatively insensitive to aging both in terms of wettability and adhesion, due to crosslinking during plasma treatment, which is likely to reduce macromolecular mobility within the surface layer.

In the case of PP, dramatic decreases of wettability occur with time, due to macromolecular motions leading to minimization of oxygen-containing functions at the surface. This behavior was shown to affect the adhesion performance of treated PP.

Oxygen plasma-treated polydimethylsiloxane surfaces were aged in a low-energy (air) and in a high-energy (water) medium. Treated samples were characterized using a combination of surface-sensitive techniques: X-ray photoelectron spectroscopy, static secondary ion mass spectroscopy, and contact angle measurements. Plasma treatments cause large increases in surface tension of treated samples. When aged in air (low-surface-energy medium) the samples returned to a low-surface-tension situation. The mechanism was a combination of diffusive burial of polar groups in the bulk and condensation of silanol groups formed by plasma treatment and consequent crosslinking. When aging was performed in water, a high surface tension was maintained.

PTFE was treated with oxygen plasma, and the effects of treatment time were evaluated by XPS, SEM, and the contact angles of water and CH₂l₂. Advancing and receding angles were interpreted in the light of current theories on contact angle hysteresis. It was found that at short treatment time wettability reflects chemical modification of the surface, while at longer treatment times surfaces are deeply etched and contact angles are controlled by roughness. With water as the wetting liquid, the typical behavior of composite surfaces was observed.

PTFE was treated with oxygen plasma, and the effects of treatment time were evaluated by XPS, SEM, and the contact angles of water and CH₂l₂. Advancing and receding angles were interpreted in the light of current theories on contact angle hysteresis. It was found that at short treatment time wettability reflects chemical modification of the surface, while at longer treatment times surfaces are deeply etched and contact angles are controlled by roughness. With water as the wetting liquid, the typical behavior of composite surfaces was observed.

PTFE was treated with oxygen and argon plasmas and the effects of treatment were evaluated by actinometry, SEM, XPS, static SIMS and contact angle measurements. At short treatment times for both plasmas and at long treatment times for argon plasmas, chemical modification of the surface was dominant, while at longer oxygen plasma treatment times, surfaces are deeply etched but chemically equivalent to untreated PTFE. Interestingly, the change in surface chemistry is paralleled by a simultaneous variation in plasma chemistry, suggesting that the two vary accordingly. The wetting behaviour of treated surfaces is interopreted on the basis of current theories on surface dynamics and contact angle hysteresis.

Oxygen plasma treatment as a surface functionalization technique is discussed. Oxygen-containing functionalities were introduced on the surface of high- (HDPE) and low-density polyethylene (LDPE) by glow discharge. The number of surface hydroxyl groups was increased by a post-discharge wet treatment in a reducing solution. The effects of the substrate nature, the discharge parameters, and the post-discharge wet treatment on the surface functional groups are discussed, and the effectiveness of functionalized surfaces on the yield of coupling reactions is shown.

It is well known that in extrusion coating, the coating adhesion to the substrate decreases with decreasing thickness. The study on this phenomenon is divided into three parts. Part I explores the reduction in adhesion of LDPE to paper and other porous substrates. Several hypotheses are proposed for the origin of this decrease, including a reduction in oxidation time, faster cooling in the air gap, and more rapid quenching in the nip. A model of the molten polymer penetration into the substrate shows that the greatest effect is cooling in the nip; thinner coatings have less time to flow into the substrate interstices once the chill roll contact is made. The model results agree well with experimental adhesion data from the literature.

In Part II, adhesion to aluminum foil and other nonporous substrates is studied. Several hypotheses are proposed for why peel strength decreases in these structures, including a reduction in the air gap time, faster air gap cooling, more rapid nip quenching, and stress imposed during drawing. Modeling and experimental results show that cooling in the nip and imposed stress have the greatest impact.

In Part III, the peel test is analyzed to understand why the peel strength of better adhering adhesives are more sensitive to changes in coating thickness. The analysis shows that changes in the critical dimension of the deformation region at the peel front may be responsible.

A theory for the current and light pulses of positive glow corona from a point in air is presented; this phenomenon was first observed as an apparently continuous glow by Michael Faraday. Results are obtained, in concentric sphere geometry, for air at atmospheric pressure, by solving the continuity equations for electrons, positive ions, negative ions and metastable oxygen molecules, coupled with Poisson's equation. A series of ‘saw-toothed’ current pulses of period about is predicted with a DC current level. Accompanying the current peaks are discrete pulses of light 30 ns wide. Successive ‘shells’ of positive ions, from successive current pulses, carry 96% of the mean current. The mean current - voltage relationship has the classic square-law form. The seed electrons required for successive pulses are detached from negative ions by metastable oxygen molecules. Photo-ionization is crucial for the discharge at the anode and for the formation of negative ions throughout the gap. The pulse frequency varies with applied voltage and is found to be approximately proportional to the positive-ion mobility. The surface electric field at the central electrode remains close to Peek's onset field. The origin of onset streamers is explained and sub-microsecond voltage pulses are found to produce streamers. The results for concentric-cylinder electrodes are described briefly.

The effect of air dielectric barrier discharge plasma treatment on the chemical structure and morphology of polypropylene (PP)film was studied using UV-VIS (ultraviolet-visible),FT-IR,(Fourier transform infrared),SEM (scanning electron microscopy)and AFM (atomic force microscopy).Polypropylene samples were printed using solvent-based gravure ink.An evaluation of the print quality criteria of the treated PP films included measurement of print density and print gloss.SEM investigated the ink laydown on the modified PP film.The results showed that after a few seconds of plasma treatment,both the surface energy and the surface roughness of the treated PP film increased.There was an increase in the absorbance at the almost-visible range,and C=C and C=O bands were found after the air discharge plasma treatment.A short plasma treatment of 15 seconds was found to bring about a dramatic increase in the print density readings,but a decrease in print gloss.The time of the air discharge plasma treatment was found to have no effect on the print density or print gloss at a high ink film thickness.The results showed that air dielectric barrier discharge plasma treatment,for a few seconds,is effective in printing and is economical for industrial use (this will be studied in detail in future work).

Positive and negative dc corona discharges in CO-air and -air mixtures were applied. Natural humid air was used. The step by step development with time of the formation of gas products after the action of the corona discharge was measured in situ. The discharge tube was situated in an IR gas cell. The IR absorption spectra were scanned from the area of the inter-electrode distance in successive time steps of the action of the discharge (about 1 min). Measurements were performed for three combinations of electrode materials, namely Mo-stainless steel, Mo-brass and Cu-brass. Reflection IR absorption spectra from the surfaces of the electrodes used were scanned after the action of the discharge. The influence of the electrode material on the development with time of the reaction products was observed. Polymer-metal complexes with possible catalytic activity are formed on the surfaces of electrodes. From measurements it resulted that the discharge processes consist of simultaneously acting volume processes of plasmochemical nature (probably initiated by electrons) and electrocatalytic surface processes on electrodes (probably initiated by photons).

The plasmochemical and/or electrocatalytical reactions of carbon monoxide with water vapour were studied. Dc corona discharge of both polarities at room temperature and temperatures enhanced up to 70°C was applied at pressures close to atmospheric.

The reaction products were analysed by IR absorption spectrometry. The main products in the gas phase were CO₂ and CH₄. The reactions are influenced by the formation of a catalytically active surface layer on electrodes. The composition of this layer depends on the polarity of electrode.

Coating of polyethylene (PE), poly(vinyl fluoride) (PVF), poly(tetrafluoroethylene) (PTFE), and poly(vinyl chloride) (PVC) films with flow discharge-polymerized acetylene was investigated. The influence of glow discharge experimental conditions on the nature of the coated layer, the films' wettability, surface roughness, and adhesive joint strength was determined. It was found that coating of these films with plasma-polymerized acetylene led to the formation of a rough, crosslinked, irremovable layer with an improved wettability. The presence of the plasma-polymerized acetylene on the film surface lead to a large improvement in the adhesive joint strength of these films with epoxy adhesive. Best results were obtained with films coated at a low acetylene flow rate. Increase in glow discharge power and treatment time lead to a further improvement.