The paper investigates the effect of corona discharge (CD) treatment on the properties of surface layer (SL) of polylactide (PLA) film. The modification of PLAwas carried out in the air and helium atmosphere and the results were compared on the basis of the assessment ofwettability, surface free energy (SFE) calculated using Owens-Wendt method aswell as the degree of oxidation (O/C) of the modified SL, determined by photoelectron spectroscopy.

The surface functionalization of polyimide (Matrimid^® 5218) films was carried out by cold plasma treatment with CF₄, N₂ and O₂ gases using a radio frequency discharge and the optimum plasma conditions were evaluated by water contact angle measurements. The surface hydrophobicity of polyimide films was obtained after CF₄ plasma treatment, while O₂ and N₂ plasma treatments contributed to the hydrophilic surface functionalization. X-ray photoelectron spectroscopy (XPS) results revealed the presence of CF_x, amino or oxygen-containing groups attached to the polyimide film surface depending on the treatment gas. A strong influence of the used plasma gas on the film roughness was determined by atomic force microscopy (AFM) measurements. The influence of the surface modification on CO₂, N₂ and O₂ gas permeation through the plasma treated films was evaluated. The permeation behaviour was characterized in terms of transport parameters, namely, coefficients of permeability, diffusion and solubility. The permeability coefficient of all plasma treated polyimide films for the studied gases (CO₂, N₂ and O₂) was found to decrease following the order of increasing the kinetic molecular diameter of the penetrant gas. Besides, the selectivity coefficient was found to be significantly increased after the plasma treatments – α_CO2/N2 was increased up to 36% and 98% for O₂ and N₂ plasma treated Matrimid^® 5218 films, respectively. The relationship between the gas permeation behaviour and the surface modification of polymer film by cold plasma was discussed.

Polydimethylsiloxane (PDMS) and glass are among the most widely used materials in biomedical and microfluidic applications. In this paper, oxygen plasma exposure was used to improve the adhesion properties of PDMS and glass. The effect of bonding quality parameters such as RF power, time of activation and oxygen flow was investigated. Bonding area and strength, two main indicators of bonding quality, were detected using manual peel and mechanical shear tests, respectively, to optimize the bonding parameters. It was observed that increase in activation time and RF power increased the bonding strength considerably. The oxygen flow had a slight influence in increasing the bonding strength. The application of this bond has also been demonstrated in PDMS–glass micropump, so this technique can be potentially applied for fabrication of PDMS–glass-based microfluidic and biomedical devices.

The optimization of heat-sealing process parameters, including time, temperature, and pressure, was performed on a monolayer linear low-density polyethylene (LLDPE) film. The seal properties examined for each process condition were: seal initiation temperature (T_si), plateau initiation temperature (T_pi), final plateau temperature (T_pf), plateau seal strength (SS_p), and failure mode. Increasing dwell time enhanced seal strength. However, it was found that the rate of this enhancement is different for each interval of dwell time. A narrow temperature plateau was observed for dwell times lower than 0.4 s and higher than 2 s, while in between a broad temperature window was observed. The pressure shows its influence up to the stage of wetting. And after providing the intimate contact between two film layers, additional increase in pressure does not enhance seal strength significantly. A 3D mapping of process safety zone was introduced for seal strength in the range of heat seal process variables for the very first time. The analysis of this 3D representation revealed that seal strength has a linear correlation with the square root of dwell time. In addition, the interfacial bond strength was shown to be proportional to the fraction of melted crystals. It was found that this fraction is determined by dwell time and temperature. Topography and morphology of surfaces after peeling revealed enlargement of fibrillar morphology to taller failure fracture complex shapes. Extensive roughness analysis on film surfaces after peeling found the much rougher surfaces after breakage of strong bonding.

This paper studies the effects on valid domain of contact angles and error limits of solid surface tension components and parameters (SSTCPs)/square roots of SSTCPs (SQSSTCPs) from the changes in liquid surface tension components and parameters (LSTCPs) when applying the van Oss–Chaudhury–Good (vOCG) approach. The results of maximum absolute errors and maximum relative errors (MREs) in SQSSTCPs/SSTCPs, induced by errors in LSTCPs or contact angles, show that most SQSSTCPs/SSTCPs can be evaluated at moderate accuracy from the lowest condition number liquid triplets, assuming that |Δθ_i| = 1° and  = 0.1 mN/m (i = 1, 2, 3, k = LW, +, −). This confirms the validity of the vOCG approach. The accuracy of each SQSSTSCP/SSTCP declines with increasing θ_i or decreasing parameter when θ_i > 0 or a critical value, provided the other two contact angles are kept fixed. This explains the underlying reasons for negative SQSSTCPs. At the scale proposed by vOCG, dimethyl sulphoxide is not suggested for use. Comparing with the MREs obtained at vOCG scale, considering the acidity of diiodomethane improves the accuracy of ; using the scales proposed by Lee and Shen do not affect the accuracy of SSTCPs, but using the scale proposed by Della Volpe et al. improves the accuracy of SSTCPs at low θ₂ and θ₃ while declines that at high ones. For a low , low surface tension apolar liquid is preferred for high accuracy. The dependence of the accuracy of SQSSTCPs/SSTCPs on contact angles suggests the importance of considering contact angle in accuracy evaluation.

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.

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.

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.

One of the major disadvantages of low density polyethylene (LDPE) films is their poor adhesive properties. Therefore, LDPE films have been treated with atmospheric pressure air plasma in order to improve their surface properties. So as to simulate the possible conditions in an industrial process, the samples have been treated with two different sample distances (6 and 10 mm), and treatment rates between 100 and 1000 mm s⁻¹. The different sample distances are the distance of the sample from the plasma source. The variation of the surface properties and adhesion characteristics of the films were investigated for different aging times after plasma exposure (up to 21 days) using contact angle measurement, atomic force microscopy, weight loss measurements and shear test. Results show that the treatment increases the polar component and these changes improve adhesive properties of the material. After the twenty-first day, the ageing process causes a decrease of wettability and adhesive properties of the LDPE films (up to 60%).

Atmospheric pressure plasma processing has attracted significant interests over decades due to its usefulness and a variety of applications. Adhesion improvement of polymer surfaces is among the most important applications of atmospheric pressure plasma treatment. Reflecting recent significant development of the atmospheric pressure plasma processing, this work presents its fundamental aspects, applications, and characterization techniques relevant to adhesion.

The current broad interest in wetting characterization of solid surfaces is driven by recent advances in the formulation of surfaces and coatings that are superhydrophobic, superhydrophilic, oleophobic, oleophilic and so on. Unfortunately, the contact angle data presented in many publications raise some concerns among the surface chemists and physicists who work with contact angle measurement techniques on a regular basis. In those articles, best practices are often ignored, and the data presented are limited to the static contact angles measured for small droplets, a few times smaller than typically recommended. The reported contact angles are neither advancing nor receding, and their reproducibility in different laboratories is therefore questionable. In this note, guidelines to measurements of reproducible and reliable advancing and receding contact angles are summarized.

In this work, air dielectric barrier discharge (DBD) operating at the line frequency (60 Hz) or at frequency of 17 kHz was used to improve the wetting properties of polypropylene (PP). The changes in the surface hydrophilicity were investigated by contact angle measurements. The plasma-induced chemical modifications of PP surface were studied by X-ray photoelectron spectroscopy (XPS) and Fourier-transformed infrared spectroscopy (FTIR). The polymer surface morphology and roughness before and after the DBD treatment were analyzed by atomic force microscopy (AFM). To compare the plasma treatment effect at different frequencies the variation of the contact angle is presented as a function of the deposited energy density. The results show that both DBD treatments leaded to formation of water-soluble low molecular weight oxidized material (LMWOM), which agglomerated into small mounts on the surface producing a complex globular structure. However, the 60 Hz DBD process produced higher amount of LMWOM on the PP surface comparing to the 17 kHz plasma treatment with the same energy dose. The hydrophilic LMWOM is weakly bounded to the surface and can be easily removed by polar solvents. After washing the DBD-treated samples in de-ionized water their surface roughness and oxygen content were reduced and the PP partially recovered its original wetting characteristics. This suggested that oxidation also occurred at deeper and more permanent levels of the PP samples. Comparing both DBD processes the 17 kHz treatment was found to be more efficient in introducing oxygen moieties on the surface and also in improving the PP wetting properties.

In this work particular attention has been paid to the aging behavior of biaxially oriented polypropylene (BOPP) film surfaces modified with the acrylic acid (AAc) corona discharge treatment previously reported. Three different corona energies of 15.3, 38.2 and 76.4 kJ/m² were studied. The surface properties of treated films during 90 days of aging were compared with those of normal air-corona treated films prepared with the same corona energies. The surface chemical compositions of aged films were analyzed by curve-fitting of the ATR-FTIR spectra. The wettabilities of all aged films were monitored by water contact angle and surface free energy measurements. The change of surface topology of air- and AAc-corona treated films was investigated at 1 day, 7 days and 90 days of aging using the technique. In addition, the surface adhesions of aged films were determined with the T-peeling test. The results showed that the amount of polar functional groups on the surface of aged films had changed. However, the aged films of the AAc-corona treated films still showed greater wettability than did the air-corona treated films and could retain high surface hydrophilicity for more than 90 days of aging under ambient condition. The surface topology of both types of aged films changed after aging from a globular structure to a flatter surface, due to mobility of the deposited polymer layer. The AAc-corona treated films showed rougher surfaces due to the influence of poly(acrylic acid) deposition and they could retain the improved surface wettability despite the change in surface topography. The adhesion peel forces of aged films decreased slightly due to the topological changes. A mechanism for the change in surface topography and in chemical functionality of each type of aged film is proposed.

Different methods used to determine the surface energy of solids from the contact angles of different liquids were compared considering their theoretical background, and multicomponent approaches were applied to polymers and surface-treated polymers containing only C, H, O and N. These methods involve different approximations and give different results regarding surface energy, supporting the view that none of them provides absolute values having the accuracy expected for thermodynamic parameters and their use in computing quantities such as the work of adhesion and interfacial energy. Nevertheless they ranked the surface polarity in the same order, which was also the order simply provided by the water contact angle. A multivariate analysis of works of adhesion deduced from measured contact angles for a set of liquids on different solids may be a relevant alternative to deterministic approaches for ranking surfaces and deciphering the factors which govern their behavior. As the acid-base interactions are involved in surface energy and are due to specific chemical functions, the relationship between the water contact angle and the surface composition was examined, using surface-oxidized polypropylene as a model case. The cosine of the water contact angle was found to correlate with the “surface” oxygen concentration determined by XPS. However, this correlation may be misleading. Actually the surfaces showing the highest oxidation and the highest apparent hydrophilicity should be regarded as covered with a layer of adsorbed compounds, rather than belonging to a defined solid phase.