In this study, the adhesion properties of adhesives and paints on wood–plastic composites (WPCs) after plasma treatment at atmospheric pressure and ambient air were investigated. Surface energy determination by means of contact angle measurements according to the Owens–Wendt approach and atomic force microscopy to detect changes in surface topography were carried out. An increase in the polar component of surface energy and an increase in surface roughness after plasma treatment were detected, indicating enhanced bond strength. To confirm these results, bond strength tests were conducted. By tensile bond strength tests, increased adhesion of waterborne, solventborne and oil-based paints on plasma treated surfaces was found. Furthermore, by shear bond strength tests, an increase in bond strength of plasma treated WPCs bonded with poly(vinyl acetate) and polyurethane adhesives was ascertained.

The van Oss–Chaudhury–Good theory (vOCGT) was checked for a large artificial set of work of adhesion input data calculated for 15 solids and 300 liquids. Numerical values of LW component and acid (A) and base (B) parameters were assigned to 15 solids. These 15 solids were grouped in 5 sets of 3 solids in each. Also numerical values of LW component and A and B parameters were assigned to 300 liquids (three sets of 100 liquids in each). Data for these solids and liquids were especially selected to represent real types of materials encountered in practice. For all 15 solids and 300 liquids the work of adhesion values were calculated and these values were assumed to be error-free. Next, new values of the work of adhesion were obtained by adding a random homoscedastic error (A vector of random variables is homoscedastic if it has the same finite variance.) of the normal distribution (Also called the Gaussian distribution — it is continuous probability distribution defined by two parameters: the mean and variance (standard deviation squared, σ²).), belonging to 8 distributions of a mean value equal to the error-free work of adhesion value and standard deviations of 0.5, 1, 2, 5, 7, 10, 15 and 20 mJ/m². The LW components and A and B parameters for these solids were back-calculated for each error level. Two different methods for the solution of a 3-equation set were used and they gave practically the same results irrespective of the error level and liquids and solids used. It was found that there existed a linear correlation between the RMSE (root mean square error) of the solution and the standard deviation of the work of adhesion data. This correlation was highly significant (with a correlation coefficient higher than 0.999) and was true separately for LW component, A and B parameters as well as for the total solution vector (i.e., combinedly for the LW component, A and B parameters). The RMSE values of the total solution vector (having as elements values of the LW component, A and B parameters) as well as separately for LW component and A and B parameters were correlated with the condition number of a given 3-equation set. A very good correlation was found only for the total solution, much worse for A or B parameters, and practically there was a lack of correlation for the LW component. Based on the correlation between the RMSE and the standard deviation of the work of adhesion it was possible to determine what should have been the maximal standard deviation of the work of adhesion if the calculated value of a given LW component or A or B parameter did not differ by more than 1 mJ/m² from an error-free (true) value.

Surface modification of thermotropic liquid crystalline aromatic polyester (LCP) films was carried out by low-pressure plasma treatment to improve the initial adhesion as well as the long-term adhesion reliability, a measure of durability between the LCP films used as substrates for printed circuit boards. Plasma irradiation was carried out in various plasma gases with different plasma modes such as reactive-ion-etching, and direct-plasma (DP) with pressures ranging from 6.7 Pa to 26.6 Pa. The introduction of polar groups on the film surface such as phenolic hydroxyl groups and carboxyl groups enhanced the initial adhesion by increased chemical interaction. However, if the concentration of polar groups became too high, the longterm adhesion reliability estimated by the pressure cooker test was degraded due to the acceleration of the penetration of water molecules into the interface. A large surface roughness was also effective in preventing the decrease in the long-term adhesion reliability. However, too much increase in surface roughness decreases the long-term adhesion reliability. The DP-treatment in the O₂ atmosphere at a gas pressure of 6.7 Pa was found to be the best plasma condition for both the initial adhesion as well as the long-term adhesion reliability between the LCP films.

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.

The poly(ethylene terephthalate), PET, film was exposed to atmospheric pressure plasma under various plasma processing parameters. The wettability of the PET film immediately after the exposure and after storage in air, which was determined by the sessile drop method, was strongly dependent on the plasma processing parameters. The contact angle hysteresis on the plasma-exposed PET film was examined by the Wilhelmy method. It was found that the hydrophobic recovery of the PET surface on storage after the plasma exposure was observed only for the advancing contact angle and that the receding angle remained almost the same. These experimental findings were explained on the basis of the calculation by Johnson and Dettre for the advancing and receding contact angles on model heterogeneous surfaces.

Plasma treatment and vacuum Al deposition on films from biaxially oriented polypropylene is a multistep large scale industrial process, mainly ending up in packaging film laminates. As atmospheric plasma treatment processes suffer from lack of reproducibility, low pressure plasma treatment processes that can be operated in-line with the metal deposition are being developed. Process development is difficult, because the final packaging film laminate has to deliver optimum properties of adhesion as well as of the barrier against oxygen and water vapor permeation. As a typical production run involves tens of thousands to up to one hundred thousand square meters of film, experiments on an industrial scale are expensive, so smaller scale experimental processes are needed, which so far do not match well enough with industrial process characteristics. Moreover, bonding mechanisms between the treated substrate film and the deposited Al layer are not sufficiently understood. This paper describes the sequence in development and optimization of substrate films and plasma treatment that has been performed on an experimental as well as on an industrial scale. A sufficient correlation between experimental and industrial scales was achieved, which helps to perform development and optimization on a small scale before scaling up to industrial processes. However, improvement is still needed both in fundamental understanding of the aluminum–polypropylene interface as well as in experimental equipment and methodology.

Interactions of cellulose fiber surfaces with water and other liquids depend on surface morphology as well as intrinsic material properties. Smooth nanocrystalline cellulose (I) films can be used as models to study surface phenomena, where the effects of surface morphology and roughness are minimized. Contact angle measurements are particularly sensitive to surface roughness. In this work, we measured the advancing and receding contact angles for water on thin model cellulose (I) and regenerated cellulose (II) films. The advancing and receding contact angles on model cellulose (I) surfaces were lower than on cellulose (II) surfaces, and the contact angle hysteresis was also lower for the smooth model cellulose (I) surfaces prepared from nanocrystal suspensions. The surface free energy was evaluated for the various cellulose surfaces from contact angle measurements.

In order to characterize a solid surface, the commonly used approach is to measure the advancing and receding contact angles, i.e., the contact angle hysteresis. However, often an estimate of the average wettability of the solid–liquid system is required, which involves both the dry and wetted states of the surface. In this work, we measured advancing and receding contact angles on six polymer surfaces (polystyrene, poly(ethylene terephthalate), poly(methyl methacrylate), polycarbonate, unplasticized poly(vinyl chloride), and poly(tetrafluoroethylene)) with water, ethylene glycol and formamide using the sessile drop and captive bubble methods. We observed a general disagreement between these two methods in the advancing and receding contact angles values and the average contact angle determined separately by each method, although the contact angle hysteresis range mostly agreed. Surface mobility, swelling or liquid penetration might explain this behaviour. However, we found that the 'cross' averages of the advancing and receding angles coincided. This finding suggests that the cross-averaged angle might be a meaningful contact angle for polymer–liquid systems. Hence, we recommend using both the sessile drop and captive bubble methods.

Measurements of the surface tension (γ_LV) and advancing contact angle () on poly(tetrafluoroethylene) (PTFE) and poly(methyl methacrylate) (PMMA) were carried out for aqueous solutions of sodium decyl sulfate (SDS) and p-(1,1,3,3-tetramethylbutyl)phenoxypoly(ethylene glycol) (TX100) and their mixtures. The results obtained indicate that the values of the surface tension and contact angles of solutions of surfactants on PTFE and PMMA surfaces depend on the concentration and composition of the surfactant mixtures. Calculations based on the Lucassen-Reynders equation indicate that for single surfactants and their mixtures at a given concentration in the bulk phase the values of surface excess concentration of surfactants at water–air and PTFE–water interfaces are nearly the same, so the adsorption of the surfactants at water–air and PTFE–water interfaces should also be the same. However, the adsorption of TX100 and its mixtures with SDS at water–air interface is higher than that at PMMA–water interface, which is confirmed by the ratio of absolute values of molecular interaction parameters at these interfaces calculated on the basis of Rosen approach. If we take into account the hydration of the poly(ethylene oxide) chains of TX100 and acid and base parameters of the surface tension of water it appears that the PMMA surface is covered by the 'pure' water molecules from the solution or molecules connected with the chain of nonionic surfactant. On the other hand, the lack of SDS molecules at the PMMA–water interface may result from the formations of its micelles which are connected with the TX100 chain.

Surface free energy (SFE) is a property which depends on the chemical state and roughness of the surface and it is necessary to develop a reliable method to evaluate SFE value on a small area, taking into account these two different contributions. Today contact angle methods are the most used and they allow to evaluate the global mean value of SFE on areas of mm² size. With these methods, it is not possible to evaluate the effects of roughness, surface defects, chemical contamination on SFE value. In addition, it is difficult to determine the surface free energy value on small components which have dimensions smaller than drop diameter. Nanoindentation and atomic force microscopy techniques provide alternative direct measurement methods to evaluate the SFE on small areas (on the order of μm² or nm²) through a contact mechanism triggered by the contact of two bodies. In order to evaluate the adhesion properties, currently three models, Johnson– Kendall–Roberts, Maugis–Dugdale and Derjaguin–Muller–Toporov, use the value of pull-off force (force required to separate the indenter tip from the sample). All influences of surface morphology on SFE values are lost using these methods. In fact the adhesion value obtained refers to the energy balance between two conformal surfaces, which depends mainly on the morphology of the harder material (i.e., diamond tip). In this work we describe a new methodology for the SFE determination consisting in the modeling and quantitative evaluation of the interaction between the tip and sample surface during the approach phase in a nanoindentation test. During the test, the nanoindenter tip is attracted to the sample surface until the sample reaction forces become significant (in this case physical contact between two bodies is achieved). The SFE value is evaluated using experimental force of attraction and displacement of the nanoindenter spherical tip when it approaches the sample surface. In this method the sample surface is not altered by the tip, therefore unlike pull-off force method, it could be very useful to evaluate the actual SFE considering the effect of sample morphology (controlled roughness or pattern).

A new concept for molecular interface design in metal–polymer systems is presented. The main features of this concept are the replacement of weak physical interactions by strong covalent bonds, the flexibilization of the interface for compensating different thermal expansions of materials by using long-chain flexible and covalently bonded spacers between the metal and the polymer as well as its design as a moisture-repellent structure for hindering diffusion of water molecules into the interface and hydrolysis of chemical bonds. For this purpose, the main task was to develop plasmachemical and chemical techniques for equipping polymer surfaces with monotype functional groups of adjustable concentration. The establishing of monotype functional groups allows grafting the functional groups by spacer molecules by applying usual wet-chemical reactions. Four processes were favoured for production of monotype functional groups by highly selective reactions: the plasma bromination, the plasma deposition of plasma polymers, the post-plasma chemical reduction of O-functionalities to OH-groups, and the chemical replacement of bromine groups by NH₂-groups. The grafting of flexible organic molecules as spacers between the metal layer and polymer improved the peel strength of the metal. To obtain maximal peel strength of aluminium coatings to polypropylene films and occurrence of cohesive failure in the polypropylene substrate, about 27 OH groups per 100 C-atoms or 6 COOH groups per 100 C-atoms were needed. Introducing C_6–11-aliphatic spacers 1 OH or COOH group per 100 C-atoms contributed about 60% of the maximal peel strength of the Al–PP system, i.e. 2 or 3 spacer molecules per 100 C-atoms were sufficient for maximal peel strength.

A low-temperature, atmospheric pressure helium and oxygen plasma has been used for the surface preparation of aluminum 2024 prior to adhesive bonding. The plasma converted the aluminum from a water contact angle (WCA) of 79° to down to 38° within 5 s of exposure, while sanding reduced the WCA to only 51°. Characterization of the aluminum surface by X-ray photoelectron spectroscopy revealed a decrease in carbon contamination from 70 to 36% and an increase in the oxygen content from 22 to 50% following plasma treatment. Similar trends were observed for sanded surfaces. Lap shear results demonstrated bond strengths of 30 ± 2 MPa for the sanded aluminum vs. 33 ± 1 MPa for plasma-treated aluminum, where sol gel and primer coatings were added to the surface preparation. Following seven days of aging, wedge crack extension tests revealed cohesive failure percentages of 86, 92, and 96% for sanded, plasma-treated, and sanded/plasma-treated aluminum, respectively. These results indicate that atmospheric pressure plasmas are an attractive alternative to acid treatment or abrasion techniques for surface preparation prior to bonding.

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.

This paper describes our investigation of the effects of forced air plasma treatment on polypropylene and polyethylene. The morphology of the treated surfaces has been carefully examined using a variety of tools including optical profiling. The complex surface morphology was observed to change with increasing treatment and varying intensity of the treatment over the surface. Optimum treatment conditions have been deduced using surface energy determinations and can be compared with the morphological changes. Determinations of surface energy, both the polar and non-polar components, have been made after exposure to varying moisture conditions for varying times. Different results are obtained for different environments and from different materials. These results demonstrate that forced air plasma treatment is a highly effective means of increasing the surface energy of polymers, which can be long-lasting, provided the treated surfaces are kept in dry conditions.

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.

A critical review of published studies investigating the dielectric barrier discharge (DBD) treatment of four polymers widely employed in the packaging sector, namely: polyethylene (PE), polypropylene (PP), poly(ethylene terephthalate) (PET) and polystyrene (PS) is presented. The DBD treatment process operates at atmospheric pressure in air, and thereby offers a low cost method of enhancing the surface properties of polymers. The method is suitable for high volume in-line applications such as packaging. It has been reported that treatment doses as low as 0.01 J/cm² result in significant increases in surface energy and wettability, leading to enhanced adhesive bonding and printing performance. Two critical issues limit the improvements obtained via the DBD processing of polymers. Firstly, DBD processing can produce a poorly adhered surface layer of low molecular weight material, which can then interfere with bonding and printing processes. Secondly, the properties of DBD treated polymers tend to revert towards that of the untreated state during storage.

Droplet dynamics analysis concerns the measurements of droplet volume, cap and base areas and contact angles, as they change in time to study evaporation, wettability, adhesion and other surface phenomena and properties. In a typical procedure, the two-dimensional measurements are based on a series of images recorded at successive stages of the experiment from a single view. Only a few basic dimensions of sessile droplets are commonly measured from such images, while many other quantities of interest are derived utilizing geometrical relationships. The reliability of these calculations is limited by the necessary assumption that the droplet shape can be approximated as a spherical cap. In reality, the sessile droplet shapes are influenced by gravity, liquid surface tension, local surface anisotropy and microstructure, which often produce non-spherical cap shapes.

This paper describes an experimental methodology for determination of key parameters, such as volume and contact angle for dynamic sessile droplets that can be approximated either by spherical or ellipsoidal cap geometries. In this method, images collected simultaneously from three cameras positioned orthogonally to each other are used to record the dynamic behavior of non-spherical droplets. Droplet shape is approximated as an ellipsoid of arbitrary orientation with respect to the cameras, which allows determination of volume and contact angle along the base perimeter. A major advantage of this method is that the dynamic parameters of droplets on anisotropic surfaces can be determined even when the orientation of the axes changes throughout the droplet lifetime. The method is illustrated with experimental results for a spherical and an ellipsoidal droplet.

In this work, the effect of medium pressure plasma treatment on thin poly-ϵ-caprolactone (PCL) layers on glass plates is investigated. PCL is a biocompatible and biodegradable polymer which potentially can be used for bone repair, tissue engineering and other biomedical applications. However, cell adhesion and proliferation are inadequate due to its low surface energy and a surface modification is required in most applications. To enhance the surface properties of thin PCL layers spin coated on glass plates, a dielectric barrier discharge (DBD) at medium pressure operating in different atmospheres (dry air, argon, helium) was used. After plasma treatment, water contact angle measurements, X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) were used to examine the PCL samples. These measurements show that the medium pressure plasma treatment is able to increase the hydrophilic character of the samples, due to an incorporation of oxygen groups at the surface and that the surface roughness is significantly decreased after plasma treatment.

In atmospheric pressure plasma treatments water molecules in the substrate material may disrupt the molecular arrangement in the substrate and thus greatly influence the outcome of the plasma treatment. This paper summarizes the results of our recent studies on how moisture influences the etching, surface chemical modification, crystallinity and aging of aramid, ultrahigh molecular weight polyethylene (UHMWPE), polyamide fibers, and poly(vinyl alcohol) (PVA) films. Overall, a higher moisture regain often results in a greatly enhanced etch rate, less surface chemical composition change, increased near-surface crystallinity, which could lead to a higher surface wettability, higher interfacial shear strength between the fibers and resin, decreased water solubility for PVA films, and delayed hydrophobic recovery of plasma treated fibers. Therefore, it is important to control the moisture contained in the substrate in atmospheric pressure plasma treatments.

Adhesion is a surface phenomenon occurring in many processes, e.g., bonding, painting or varnishing. Knowing the adhesion properties is critical for evaluating the usability or behaviour of materials during these processes. Good adhesion properties favour the processes of bonding, resulting in high strength of adhesive joints. Adhesive bonded joints are used in many industries, and the subject of this study was 7075 aluminium alloy sheet bonded joints as typically used in the aviation or construction industry. Surface free energy (SFE) can be used to determine the adhesion properties of the materials. The SFE of the tested sheets was determined with the Owens–Wendt method, which consists in determining the dispersion and polar components of SFE. The purpose of this work was to correlate the bonded joint strength of selected aluminium alloy sheets to the surface free energy of the sheets that had been subjected to degreasing only and no other prior treatment was used. Single-lap bonded joints of 7075 aluminium alloy sheets were tested. Higher joint strength was measured for the thinner sheets, while the lowest strength was measured for the thickest sheets. This suggests that the thickness of the joined parts is an important factor in the strength of bonded joints. The comparison of adhesion properties to the strength of adhesive joints of tested materials shows that there is no direct relation between good adhesion properties (i.e., high SFE) and joint strength. As for degreasing, the highest joint strength was observed for aluminium alloy sheets with the lowest SFE; the sheets which were not degreased gave the highest SFE and highest joint strength.

Corona, flame, atmospheric plasma, and liquid flame spray (LFS) techniques were used to create highly hydrophilic surfaces for pigment-coated paper and board and machine-glossed paper. All the surface modification techniques were performed continuously in ambient atmosphere. The physical changes on the surfaces were characterized by field emission gun-scanning electron microscopy (FEG-SEM), atomic force microscopy and Parker Print-Surf surface roughness. The chemical changes were analysed by X-ray photoelectron spectroscopy. The superhydrophilic surfaces, i.e. contact angle of water (CAW) <10°, were created mainly by modifying the surface chemistry of the paper and board by argon plasma or SiO2 coating. The nano- and microscale roughness existing on paper and board surfaces enabled the creation of the superhydrophilic surfaces. Furthermore, the benefits and limitations of the surface modification techniques are discussed and compared. For example, the SiO2 coating maintained its extreme hydrophilicity for at least six months, whereas the CAW of argon plasma-treated surface increased to about 20° already in one day.

In the case of the peeling of adhesive tapes from soft adherends, the contributions of the compressive force at the adhered portion as well as the larger deformation of adherend have essential roles in determining the peeling properties. In this paper, the peel force of an adhesive tape from a soft adherend has been measured to understand the peeling mechanism, which is greatly affected by the peel angle. A commercially available pressure-sensitive adhesive was used as the tape, and a cross-linked polydimethylsiloxane (PDMS) was used as the soft adherend. The purpose of this study is to clarify the effects of the peel angle on the peel behavior of this system at room temperature under different material specifications and different experimental conditions. The factors that affect the peel force of the PDMS adherend included the degree of cross-linking in PDMS, the thickness of PDMS, peel angle, and peel velocity. Two characteristic peel patterns were observed, which depended on the material specifications and different experimental conditions. The peel mechanism was discussed in terms of the deformation of the adherend.

Polystyrene (PS) was treated with vacuum UV (VUV) (λ = 104.8 and 106.7 nm) photo-oxidation and X-ray photoelectron spectroscopy detected a controlled increase in the atomic percentage of oxygen up to a saturation level of ca. 20 at% O. Initially, C–O and carbonyl groups are observed due to the formation of alcohols, ethers, esters, and ketones. Water contact angle measurements showed ca. 25% increase in hydrophilicity of the surface with oxidation. Atomic Force Microscopy observed little changes in surface roughness with treatment time. The super water absorbent polymer poly(acrylic acid) was thinly grafted to the modified PS surface.

The uncertainty in contact angles from sessile drops measured by the tangent method was estimated using a standard error propagation technique involving partial derivatives. If contact angles are <60°, then uncertainty of the tangent method appears to be quite small,≤ ± 2°. However, as θ values approach 90°, uncertainty increases asymptotically and can exceed  ±5°.

The effect of atmospheric pressure plasma treatment on the adhesion between a protective coating and AA1100 alloy was investigated. Two plasma sources were used for surface modifications: atmospheric pressure plasma jet and dielectric barrier discharge. The surface roughness and water contact angle measurements were conducted in order to evaluate the changes on the aluminium surface after plasma processing. The paint coating was tested using the adhesion tape test (ASTM D3359). A significant improvement of surface wettability and adhesion was obtained after plasma treatments.

The uncertainty in contact angles from the Wilhelmy tensiometer was analyzed using standard error propagation techniques involving partial derivatives across the full range of wettability, from completely wetting to non-wetting surfaces. Uncertainties in force, sample perimeter, and liquid surface tension of 1% were shown to yield uncertainty in contact angles of a few degrees over the middle range of wettability, but exceeded 10° at the extremes.