One technique for the experimental determination of the dispersion and polar contributions to solid tension, γ_s ^d and γ_s ^p , is to measure the contact angle θ of a set of m liquids of known dispersion and polar contributions to surface tension on the solid and then to calculate γ_s ^d and γ_s ^p . There are two common techniques for this calculation, graphically¹ or analytically.^2,3 The graphical technique is limited in that it only considers dispersion forces (i.e., nonpolar systems) and so only isolates γ_s ^d . For this reason the analytical procedures which isolate both γ_s ^d and γ_s ^p are more commonly used, and they can be expressed in matrix notation as:

>where A is a 2 × 2 matrix containing information about the characterizing liquids and their contact angles, and the vector ◯ is related to γ_s ^d and γ_s ^p . Equation (1) is solved for all ^mC₂ different liquid pairs to give a set of values for γ_s ^d and γ_s ^p which can then be subjected to statistical analysis.

Kevlar 149 fibers were surface-modified by NH₃, O₂, and H₂O plasmas to improve the adhesion to epoxy resin. Poly(p-phenylene terephthalamide) (PPTA) film prepared from Kevlar 149 fibers was also modified to estimate the changes in surface energy caused by the plasma treatments. The interfacial shear strength (IFSS) between the fiber and epoxy resin was measured by the microbond pull-out test. The fracture surfaces of microbond pull-out specimens were examined by scanning electron microscopy (SEM) to identify the failure mode of the microcomposites. The results showed that the IFSS of the Kevlar 149 fiber/epoxy resin system was remarkably improved (up to a factor of 2.42) by these plasma treatments and the treatment time was the governing factor in improving the IFSS. After the plasma treatments, the fracture mode of the microcomposites changed from failure at the interface to failure either in the fiber skin or in the epoxy resin. The surface free energy and the work of adhesion of water on the PPTA surface were markedly improved by the plasma treatments. The polar component of the surface free energy and the acid-base (non-dispersion) component of the work of adhesion made an important contribution to the improvement. Some correlations between the IFSS and the surface energies were found.

Kevlar 149 fibers have been surface treated with NH₃-, 0₂-, or H₂O-plasm to modify the fiber surfaces. SEM (scanning electron microscopy) is used to characterize the surface topography of fibers etched by gas plasmas. The chemical compositions and functional groups of the fiber surfaces are identified by ESCA (electron spectroscopy for chemical analysis) and SSIMS (static secondary ion mass spectroscopy), respectively. The contact angle of water on modified PPTA [poly(p-phenylene terepbthalamide)] film prepared from using Kevlar 149 fibers is also used to investigate the wettability. The results show that the etching abilities of gas plasmas are dependent on the type of gas used for plasma treatments. The contact angle data indicate that all the three gas plasma treatments are effective in rendering the surface of PPTA more hydrophilic. The ESCA analysis results show that the surface compositions of plasma-treated fibers are highly dependent on the type of gas used and treatment time. Changes in surface compositions of fibers treated by NH₃-, O₂-, and H₂O-plasma are observed. Increasing nitrogen and oxygen contents are observed for the NH₃-plasma treatment, and the O₂- and H₂O-plasma treatments, respectively. Furthermore, the incorporation of amino groups into fiber surfaces by NH₃-plasma treatment and the extensive damage of the aromatic ring and the polymer backbone by H₂O-plasma and O₂-piasma are evidenced by SSIMS.

Hydrophilic polymer surfaces are desirable for many applications, such as adhesion and wettability. In this study, we have developed a tenaciously bound hydrophilic surface coating which can be applied to a hydrophobic polymer using a plasma treatment process. In this process, porous polyethylene (PE) was used and pretreated with the plasma discharge of an oxidizing gas, eg carbon dioxide. The treated surface, containing mainly anionic groups, was then soaked in a polycation solution, eg polyethyleneimine (PEI). A tenaciously bound hydrophilic coating was formed due to multiple anchors (ionic interactions) between PEI and the plasma-treated surface. The coated surface was characterized using water contact angle goniometry and X-ray photoelectron spectroscopy (XPS). Both the stability and the durability of the coating have been evaluated using various storage conditions and repeated washing in water. The coating process developed in this study is useful in many applications which require a permanent and lasting wettable polymer surface.

Adhesion of evaporated Cu to Teflon PFA (polytetrafluoroethylene-co-perfluoroalkoxy vinyl ether) was greatly enhanced by plasma pretreatment. The efficiency of the treatment decreased in the following order: N₂ > O₂ > (N₂ + H₂) > (O₂ + H₂) > H₂. X-ray photoelectron spectroscopy (XPS) showed the loss of fluorine and the incorporation of oxygen and nitrogen at the polymer surface. Among the gases, H₂ was found to be the most efficient for fluorine elimination, and (N₂ + H₂) for surface functionalization. Based on this investigation, it is proposed that Cu reacts with both oxygen and nitrogen to form, respectively, Cu-O and Cu-N bonds at the interface but no reaction occurs with carbon and fluorine. While greater enhancement in polymer surface wettability and stronger interfacial reactions can account for the higher performance of N₂ over O₂ in improving adhesion, these effects cannot explain the lower efficiency of H₂. Several possibilities are discussed, including surface cleaning, oxygen incorporation and the formation of weak boundary layers.

The surface modification of poly(ethylene terephthalate) (PET) and UV-cured tripropyleneglycol diacrylate (acrylic) films induced by remote N₂ and Ar microwave plasmas (2.45 GHz) was compared by in-situ XPS measurements. Both N₂ and Ar plasma treatments led to destruction of the initial oxygen-containing groups. The destruction of ester groups was much faster for the acrylic than for the PET film, and the destruction of ether groups was much faster than that of ester groups within the acrylic film. Among the plasma gases, N₂ was more effective than Ar in the case of PET, but their difference was negligible in the case of the acrylic film. The higher stability of the PET surface was attributed to the presence of a rigid aromatic backbone, which protected the ester groups from plasma UV irradiation and stabilized the free radicals. The lower stability of the acrylic film was associated with the presence of weak ether groups. New functional groups were created, attributed to carbonyl in the case of Ar, and carbonyl/amide and amine in the case of N₂ plasma treatments. The formation of these new functional groups was very small compared with the loss of ether and ester groups, suggesting that the destruction of these oxygen-containing groups proceeded mainly through elimination of the entire groups.

In the present work, contact angles formed by drops of diethylene glycol, ethylene glycol, formamide, diiodomethane, water, and mercury on a film of polypropylene (PP), on plates of polystyrene (PS), and on plates of a liquid crystalline polymer (LCP) were measured at 20°C. Then the surface energies of those polymers were evaluated using the following three different methods: harmonic mean equation and geometric mean equation, using the values of the different pairs of contact angles obtained here; and Neumann's equation, using the different values of contact angles obtained here. It was shown that the values of surface energy generated by these three methods depend on the choice of liquids used for contact angle measurements, except when a pair of any liquid with diiodomethane was used. Most likely, this is due to the difference of polarity between diiodomethane and the other liquids at the temperature of 20°C. The critical surface tensions of those polymers were also evaluated at room temperature according to the methods of Zisman and Saito using the values of contact angles obtained here. The values of critical surface tension for each polymer obtained according to the method of Zisman and Saito corroborated the results of surface energy found using the geometric mean and Neumann's equations. The values of surface energy of polystyrene obtained at 20°C were also used to evaluate the surface tension of the same material at higher temperatures and compared to the experimental values obtained with a pendant drop apparatus. The calculated values of surface tension corroborated the experimental ones only if the pair of liquids used to evaluate the surface energy of the polymers at room temperature contained diiodomethane. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1831–1845, 2000
https://onlinelibrary.wiley.com/doi/abs/10.1002/(SICI)1097-4628(20000620)76:12%3C1831::AID-APP14%3E3.0.CO;2-Q

In this paper, several acrylic pressure-sensitive adhesives (PSAs) were studied through adhesion tension relaxation (ATR) technique introduced by Kasemura and Takahashi. These acrylic PSA samples were also analyzed through static contact angle, surface free energy, dynamic contact angle hysteresis, and peel force measurements. The study has shown that the acrylic PSAs are multicomponent polymeric systems which reorient their surface segments so as to minimize interfacial tension in response to environmental changes. Therefore, it is important to consider the mobility of the surface segments of PSAs in understanding their contact angle hysteresis. Further, the ATR technique has proven to be useful in estimating such mobility.

This paper follows the “defense” of the Good-van Oss-Chaudhury (GvOC) acid-base approach made in Part I and carries out a detailed analysis of the Zisman critical surface energy and, mainly, of the Neumann equation-of-state (EQS) theory. The analysis is made on both a “practical” and a theoretical basis, trying to highlight the acceptable fitting results of axisymmetric drop shape analysis (ADSA) methods and their independence of the assumed thermodynamic foundations of EQS. Some new and original criticisms of the EQS approach are raised and it is shown that other purely semiempirical models, represented by different fitting equations with the same number of parameters, can represent the data measured by ADSA method with the same goodness as EQS. The equation of state appears as one of many semiempirical approaches for the evaluation of surface free energy of solids. Independent of the previous analysis, the criteria used in ADSA measurements are evaluated and some comments made on them.

Atmospheric pressure plasma treatment of the surface of a polypropylene film can significantly increase its surface energy and, thereby improve the printability of the film. A laboratory-scale dielectric barrier discharge (DBD) system has therefore been developed, which simulates the electrode configuration and reel-to-reel web transport mechanism used in a typical industrial-scale system. By treating the polypropylene in a nitrogen discharge, we have shown that the water contact angle could be reduced by as much as 40° compared to the untreated film, corresponding to an increase in surface energy of 14 mNm⁻¹. Ink pull-off tests showed that the DBD plasma treatment resulted in excellent adhesion of solvent-based inks to the polypropylene film.

Polymer films of poly(ethylene terephthalate), polypropylene, and cellophane were surface treated with tetrafluoromethane plasma under different time, power, and pressure conditions. Contact angles for water and methylene iodide and surface energy were analyzed with a dynamic contact angle analyzer. The stability of the treated surfaces was investigated by washing them with water or acetone, followed by contact angle measurements. The plasma treatments decreased the surface energies to 2–20 mJ/m² and consequently enhanced the hydrophobicity and oleophobicity of the materials. The treated surfaces were only moderately affected after washing with water and acetone, indicating stable surface treatments. The chemical composition of the material surfaces was analyzed with X-ray photoelectron spectroscopy (XPS) and revealed the incorporation of about 35–60 atomic % fluorine atoms in the surfaces after the treatments. The relative chemical composition of the C ls spectra's showed the incorporation of —CHF— groups and highly nonpolar —CF₂— and —CF₃ groups in the surfaces and also —CH₂—CF₂— groups in the surface of polypropylene. The hydrophobicity and oleophobicity improved with increased content of nonpolar —CF₂—, —CF₃, and —CH₂—CF₂— groups in the surfaces. For polyester and polypropylene, all major changes in chemical composition, advancing contact angle, and surface energy are attained after plasma treatment for one minute, while longer treatment time is required for cellophane. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1591–1601, 1997
https://onlinelibrary.wiley.com/doi/abs/10.1002/(SICI)1097-4628(19971121)66:8%3C1591::AID-APP21%3E3.0.CO;2-5

Transmission electron microscopy and X-ray photoelectron spectroscopy (XPS) were used to characterise thin metal films (Mg, Al, Cu, Ag) thermally evaporated onto polyethylene terephthalate (PET) and to study the formation of the Al/PET interface. The adhesion was measured with a 180° peel test technique. XPS spectra show that the Al atoms react preferentially with the carboxylic group of the PET and that the Al/PET interface exhibits a pseudo layer-by-layer growth mechanism. Two factors strongly favour the increase of metal/PET adhesion: (1) a PET temperature higher than 100°C during metal deposition (Al, Cu and Ag) and (2) a partial pressure of oxygen higher than 10⁻⁵ mbar for the Al evaporation. Furthermore, atomic metal diffusion tends to increase the adhesion while cluster segregation within the PET skin decreases the metal/PET adhesion.

Preliminary results are presented on hydrophilization, grafting, and metal plating of PP nonwovens using novel types of atmospheric-pressure low-temperature plasma sources, namely the "Surface Discharge Induced Plasma Chemical Processing" source and the plasma source based on a coplanar diffuse surface discharge. The plasma sources generate a thin (~ 0.3 mm) surface layer of plasma and are capable of meeting the basic on-line production requirements for surface activation and permanent hydrophilization of light-weight nonwovens.

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.

An atmospheric pressure glow discharge (APGD) was used for surface modification of polyethylene (PE) and polypropylene (PP). The discharge was generated between two planar metal electrodes, with the top electrode covered by a glass and the bottom electrode covered by the treated polymer sample. The discharge burned in pure nitrogen or in nitrogen-hydrogen or nitrogen-ammonia mixtures. The surface properties of both treated and untreated polymers were characterized by scanning electron microscopy, atomic force microscopy, surface free energy measurements and x-ray photoelectron spectroscopy. The influence of treatment time and power input to the discharge on the surface properties of the polymers was studied. The ageing of the treated samples was investigated as well. The surface of polymers treated in an APGD was homogeneous and it had less roughness in comparison with polymer surfaces treated in a filamentary discharge. The surface free energy of treated PE obtained under optimum conditions was 54 mJ m^-2 and the corresponding contact angle of water was 40° the surface free energy of treated PP obtained under optimum conditions was 53 mJ m^-2 and the contact angle of water 42°. The maximum decrease in the surface free energy during the ageing was about 10%.