PTFE foils were plasma-treated in order to enhance their adhesion to thin films. The effect of plasma treatment using argon and oxygen discharge gases on the surface energy of PTFE foils was examined by measuring the contact angles of water droplets placed on the foil surface. Exposure to the plasma for only about 10-20 s was very effective in enhancing the surface energy. By depositing gold films onto the PTFE substrates, it was found that this enhancement in surface energy was directly related to an increase in the film adhesion. It was also found that Ar plasma treatment of a few tens of seconds followed by O₂ plasma treatment for 10 s was even more effective for adhesion enhancement.

As discussed in Chapter 1, it has been recognized for many years that the establishment of intimate molecular contact is a necessary, though sometimes insufficient, requirement for developing strong adhesive joints. This means that the adhesive, and primer if one is employed, needs to be able to spread over the solid surface, and needs to displace air and other contaminants that may be present on the surface.

Contact angle measurements have been widely used^1–6 to calculate the values of the dispersion force, γ ^d _s , and polar force, γ ^p _s , components to the total surface free energy of a material using a derivation originally proposed by Kaelble.² In this analysis a pair of simultaneous equations is derived which for two liquids, i and j, on a common solid surface may be written as:

where α is the contact angle of the liquid on the solid surface. Thus, if the values of α, γ ^d _l , γ ^p _l and γ _l (where γ _l = γ ^d _l + γ ^p _l ) for the two liquids are known, these equations may be solved to yield the dispersion, γ ^d _d ;, and the polar, γ ^d _s , force components to the surface free energy of the solid surface. The total surface free energy, γ _s , is then simply the sum of these components.

Such polymers are commonly used as release coatings for pressure sensitive adhesive tapes. In this paper the bulk, surface, and interfacial structures of polyvinyl N-alkyl carbamates having either decyl or octadecyl side chains are examined. The bulk structures and thermal transitions were characterized using X-ray scattering and differential scanning calorimetry. Dynamic mechanical thermal analysis was used to investigate thermal transitions and rheology (i.e., segmental mobility) of the polyvinyl N-alkyl carbamates. The surface energies of polyvinyl N-alkyl carbamate coatings were determined using contact angle methods, while X-ray photoelectron spectroscopy and static secondary ion mass spectrometry were employed to characterize the near-surface compositional profiles of the coatings. The peel force provided by the polyvinyl N-alkyl carbamate coatings, as a function of aging time and temperature, was measured for a tape having an acrylic acid containing alkyl acrylate based pressure sensitive adhesive. The changes in peel force with aging time and temperature were related to the ability to maintain a stable interfacial structure between the PSA and polyvinyl N-alkyl carbamate coatings. Changes in the interfacial composition upon aging were characterized by comparing the surface compositions of the PSA and polyvinyl N-alkyl carbamate coatings initially, prior to contact, as well as after aging and peeling them apart. The increase in peel force upon aging can be attributed, in large part, to a restructuring at the PSA/polyvinyl alkyl carbamate interface. Energetically favorable acid-base interactions between the basic urethane and acetate groups in the polyvinyl alkyl carbamates and the acrylic acid groups in the PSA provide a driving force for the restructuring. If the segmental mobility within the polyvinyl alkyl carbamate is sufficient, restructuring can occur, leading to increased concentrations of these groups at the PSA/polyvinyl alkyl carbamate interface, resulting in higher attractive forces and greater adhesion. The propensity for the polyvinyl N-alkyl carbamate coatings to restructure upon contact with a polar medium was also characterized by monitoring the receding contact angle of water, as a function of water contact time and temperature. A good correlation is seen between the ability of the polyvinyl alkyl carbamate coatings to provide a low peel force for the acrylate PSA tape and the ability of the coatings to maintain a high water receding contact angle.

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 process for corona treating a polymer is described. The process involves exposing at least one surface of an article comprising a polymeric material selected from the group consisting of fluoropolymers, polycarbonates, and polyimides to a corona discharge in an atmosphere containing nitrogen and about 0.01 to about 10 percent of an additional gas selected from the group consisting of hydrogen, ammonia and mixtures thereof.

According to Bikerman, who attributes failure in adhints to a weak boundary layer, it is almost impossible and meaningless to correlate adhesive strength to surface-chemical properties of adhints. Though his assertion seems to be confirmed by the recent studies of Schonhorn and his coworkers on the methods of CASING and TCR, not a few results have yet been accumulated, which show a close relation between them. In this paper surface-chemical criteria for the optimum adhesion are investigated and the minimum interfacial tension or the maximum wetting pressure is deduced from the published data and our own as a first approximation. It is emphasized that, when critical surface tension γ _c would be used as a measure of surface-chemical properties of solid, its variability according to liquid series (nonpolar, polar and hydrogen bonding liquids) should be carefully taken into consideration. The importance is shown for polyethylene and its fluorine substituted polymers, using newly measured contact angle data and Zisman's data. Results of Levine et al. and Schonhorn et al. on adhesive shear strength with epoxy adhesives are replotted against available values of γ _c obtained by the use of hydrogen bonding liquid (γ _c ^c ), which are thought to reflect wetting behaviors of epoxy adhesives quite well. Each curve shows a maximum around γ _c ^c = 40 dyne/cm with few points falling off the curves.

The effect of Ar, Ar/C2H5OH, O2 and Ar/O2 RF (13.56 MHz) plasma treatments on surface free energy and morphology, optical properties and adhesion of polycarbonate (PC) substrates has been studied. Changes in the surface properties were followed as a function of the plasma treatment time. The polar and dispersion components of the polymer free surface energy were determined on the basis of the theory of Owens, Wendt, Kaelble and Uy. It was found that all RF plasma treatments led to an increase in the polar component of PC, mainly due to an increased hydrogen bonding ability. The increase in surface free energy reached its maximum at short plasma treatment with 3:1 gas mixture of Ar/O2. This treatment also led to pronounced improvement of the adhesion of thin SiO2 films plasma deposited on modified PC substrates, while the treatments with pure oxygen or Ar/ethanol plasma had negative effect on the adhesion.

By applying a simple device comprising a power supply for arc welding and a plasmajet torch, a new method for plastic surface treatment to improve adhesion of the plastic was developed. The method enables such surface treatment instantly in the air atmosphere by applying the plasmajet to test pieces and is effective to various k-inds of plastics, especially to crystalline plastics as polyethylene.

When several pieces of polyethylene were treated under the following conditions in our experiment, the contact angle of water on the surface was improved from 80" to 20" and the adhesive strength by the tensile test was also remarkably improved from a few kg/cm2 to 120kg/cm2.

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.

Corona treatment is an essential process used in the flexible packaging industry to improve adhesion on low surface-energy polymers. This paper explores how corona treatment prepares polymers for adhesion, how surface energy correlates to a good bond, forms of measurement and common pitfalls to avoid. By understanding the function of corona treatment and the science of the bond, converters can achieve consistent adhesion in printing, coating and laminating applications.

Gas plasma treatment of poly(ethylene terephthalate) nonwoven (NW–PET) was used to increase the hydrophilicity of single- and multilayer NW–PET. NW–PET was treated with a pulsatile CO₂ or with a pulsatile H₂O glow discharge. X-ray photoelectron spectroscopy (XPS) showed significantly more oxygen with CO₂ glow-discharge-treated NW–PET than with H₂O glow-discharge-treated-NW–PET surfaces. Moreover, the introduction rate of oxygen at a single layer of NW–PET was higher for a CO₂ than for a H₂O glow-discharge treatment. Titration data revealed significantly higher surface concentrations of carboxylic groups for CO₂ glow-discharge NW–PET than for H₂O glow-discharge-treated NW–PET. Mass spectrometry analysis revealed that the entire internal surface of a single layer of NW–PET was modified. XPS and contact measurements confirmed the modification of the internal surface of multilayers of NW–PET. H₂O and CO₂ glow-discharge-treated substrates consisting of six layers of NW–PET had a nonuniform surface concentration of carboxylic acid groups as determined with titration experiments. The outside layers of the substrate contained a higher surface concentration of carboxylic acid groups than did the inside layers. XPS analysis and titration data showed that the rinsing of H₂O and CO₂ glow-discharge-treated NW–PET with water changed the surface composition considerably. Part of the carboxylic acid group-containing species were washed off. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 480–494, 2000
https://onlinelibrary.wiley.com/doi/abs/10.1002/(SICI)1097-4628(20000124)75:4%3C480::AID-APP3%3E3.0.CO;2-9

It is shown that the best fit of experimental data to the correlation equation as used by Fowkes¹ cannot be considered as a criterion of correctness with which the mathematical formula expresses the way of polar interaction at interfaces. Examples of other evidence are given that the polar part of work of adhesion may be well represented by the geometrical mean of polar components of surface energies.

Methods for the surface free energy determination of solids based on wetting by liquids are reviewed. Some critical remarks and new ideas are included.

In recent years much emphasis has been placed on the importance of specific interactions in determining a wide range of polymer properties. Following the work of Fowkes and coworkers,^1,2 all non-dispersion force interactions falling into the “specific” category may be considered to arise from acid/base interactions. This places heavy emphasis on methods for determining suitable acid/base parameters for polymers, with inverse gas chromatography (IGC) as a convenient choice. The IGC approach employed by one of us³ uses Gutmann's theory⁴ of (Lewis) acids and bases, and determines polymer interaction properties by placing these in contact with vapors of selected fluids for which acidlbase indexes, AN and DN, are available. Retention volume data for interacting vapor/polymer combinations are compared with the retention volumes of dispersion-force probes (e.g., n-alkanes), leading to the identification of AN and DN parameters for the polymer.³

Polymeric solid surfaces were prepared by a radiation-induced graft copolymerization technique using various mixtures of 2-hydroxyethyl methacrylate (HEMA) and ethyl methacrylate (EMA). Low-density polyethylene (PE) films were used as graft substrates. Contact angles on these polymeric surfaces were determined in air and under water. The critical surface tension (γ_c) of each polymeric surface in air was estimated by the Zisman method. Geometric mean and harmonic mean approximation methods were utilized to estimate the dispersion force contribution (γ_s^d) and the polar contribution (γ_s^p) to the total surface free energy (γ_s) from contact angle data in air. The geometric mean approximation was also used to estimate γ_s^d′ and γ_s^p′ from contact angles under water. The calculated values of γ_s^d, γ_s^p are strongly dependent on the pair of liquids chosen for the calculation regardless of the approximation adopted. The values of γ_s, calculated as the sum of γ_s^d and γ_s^p, are close to the γ_c values and are less dependent on the pair of liquids used. A comparison of the ratio γ_s^d/γ_s^p for the same surface in air and under water suggests that major polymer chain conformational changes occur, particularly with respect to the hydroxyl side chain, when such surfaces are immersed in water.

Surface modification of polystyrene derivatives by ozone (O3) was investigated by in situ FT-IR spectroscopy. Polystyrene (PS) and its derivatives, poly (4-methyl polystyrene)(P4MS) and poly (α-methyl polystyrene)(PαMS) were used to compare the surface modification by O3 at different temperatures. Polymer film of 5 µm thickness was exposed to 3026 ppm of gaseous O3 in the FT-IR cell heated in the range of 0–70◦ C. Then, in situ FT-IR spectra of these films were measured under O3 exposure. It was found that the IR band assigned to C= O stretching appeared in PS and P4MS with a weak dependence on temperature; but the appearance of the C= O band was strongly dependent on temperature in the case of PαMS. The O3 reactivity of PαMS was rather lower than that of polyethylene (PE). These results strongly suggested that thermally decomposed O3 species attacked the main chain of the PS and P4MS at high temperatures. Furthermore, we investigated the surface properties of these polymer films before and after the O3 modification by AFM and water contact angle. Evidence was shown that thermal ozonolysis process for PαMS having methyl group on the polymer main chain was depressed.

The capacity of a cold atmospheric-pressure air plasma (CAAP) device for advanced first aid is presented. Using swine as an animal model, two trials: 1) a large, curved cut in hindquarters area and 2) amputation of a front leg, were performed. Cold atmospheric-pressure air plasma effluent, which carries reactive oxygen species (ROS) atomic oxygen (OI), is applied for wound treatments. Swift hemostasis of the wounds by the CAAP treatment was demonstrated. The pressure applied by a finger on the cut arteries in trial 1 and the tourniquet applied in trial 2 could be removed immediately after the treatment and there was no re-bleed in both cases. CAAP hemostasis mechanism was explored via in-vitro tests. The tests on sodium citrate mixed blood-droplet samples show that 1) the heat delivered by the CAAP has no impact on the observed clot formation, 2) plasma effluent activates platelets to promote coagulation state and cascade, and 3) the degree of clotting increases with the total amount of applied OI by means of the CAAP effluent. It took only 16 s of the CAAP treatment to reach full clotting, which was considerably shortened from the natural clotting time of about 25 minutes. The tests on smeared blood samples show that the reduction of the platelet count and the increase of RBC count are proportional to the amount of applied OI. A plausible CAAP hemostasis mechanism is concluded from the in vitro test results and the animal model trials.

Any desired surface wettability of a plastic surface can be produced by changing the concentration of the plasma gas, which here is a mixture of oxygen and a compound which includes fluorine. In the plasma treatment, the use of a third electrode consisting of a metal mesh for ion trapping can significantly decrease the etching effect. The plastic surface wettability, given by the contact angle of a water drop, does not have any direct relationship with the surface roughness due to etching in this experiment.

Many useful processes for treating solid surfaces can be carried out by plasma methods. However, most previous work was done at low pressure, usually less than a few torr. For such low pressure processes, the vacuum apparatus requires great cost and is not suitable for the treatments of large scale substrates such as long film rolls. We previously reported that surface fluorination and thin film deposition could be carried out with the atmospheric pressure glow plasma (APG) process [1]. This approach can reduce apparatus costs and can also be applied to high vapor pressure substances such as gum, textiles and biomaterials. In this article, we will discuss the mechanism of stabilization of glow plasma at atmospheric pressure and report examples of applications of this technology.

Improving wettability of the polycarbonate (PC) surface to triple distilled water has been carried out by Ar+ ion irradiation with blowing oxygen gas. The amount of Ar+ was changed from 1014 to 5 × 1016 ions/cm2 at 1 keV energy by a Kaufman-type ion source. Contact angle of the water to PC has been reduced from 78° to 50° with Ar+ irradiation, and to 12° with Ar+ irradiation in various vacuum pressures adjusted by oxygen gas flow rate (0-4 sccm). Strong O-H stretching vibration peaks at about 3370 cm−1 on FT-IR spectra of the polymer appeared after the surface treatments, and the wetting angle of the treated PC was returned to its value (78°) when the PC was exposed in air environment. The minimum contact angles were maintained with the same value when the irradiated polymers were kept in dilute HCl solution. The improved wettability and surface chemical reaction by Ar+ ion irradiation with oxygen was explained by the formation of a hydrophilic functional group. Enhanced adhesion between aluminum and PC was confirmed by the scotch tape test, and was discussed with relation between the hydrophilic group on the polymer surface and the deposited metal.

Ion irradiation with various oxygen flow rates has been carried out to improve the wettability of polymethylmethacrylate (PMMA) to water and to enhance the adhesion between Al and the polymer. Ar+ ion and oxygen ion were irradiated on the polymer, and amounts of ions were changed from 5 × 1014 Ar+/cm2 to 5 × 1016 Ar+/cm2 by a broad ion beam source. Oxygen gas from 0 ml/min to 7 ml/min was flowed near the polymer surface during the ion irradiation, and the energy of ions was changed from 500 eV to 1500 eV. The wetting angle was reduced from 68° to 49° with the Ar+ ion irradiation only at 1 keV energy, to 43° with the oxygen ion irradiation, and dropped to 8° with Ar+ ion irradiation with flowing 4 ml/min oxygen gas near the polymer surface. Changes of wetting angle with oxygen gas and Ar+ ion irradiation were explained by a two-step chemical reaction among polymer matrix, energetic ions, and oxygen gas. The effects of Ar+ ion and oxygen ion irradiation were explained by considering formation of hydrophilic groups due to a reaction between irradiated polymer chain by energetic ion irradiation and blown oxygen gas, and enhanced adhesion between Al and PMMA was explained by the formation of electron acceptor groups in polymer and electron donors in metal, and by the chemical reaction in the interface between irradiated polymer surface and deposited metal.

A new surface modification technique, the so-called ion-assisted reaction (IAR), has been developed; such modification of polymer surfaces offers many industrial applications. The addition of new functional groups on polymer surfaces and permanent hydrophilic polymer surfaces (water contact angle below 30° and surface energy 60-70 mJ/m²) have been accomplished by IAR treatment. The formation of functional groups is significantly dependent on the flow rate of the reactive gas, the irradiating ion dose, and the ion beam energy. Improvements in wettability and surface energy are primarily attributed to the increase of polar characteristics due to the formation of functional groups such as (CO), (CO)O, (CO), etc. The characteristics of the IAR treatment have been reviewed, with outstanding results regarding the wettability and adhesion of various polymers such as PMMA, PC, PP, PS, PI, PVDF, and PTFE.