The effects of the specimen temperature of low-density polyethylene (LDPE) in O₂ plasma treatment were studied to enhance the amount of hydrophilic functional groups introduced and to reduce the aging effect. The specimen temperature was varied from 25°C to 100°C. The smallest water contact angle was obtained with the 45°C specimen and the largest amount of hydrophilic functional groups was introduced with the 100°C specimen, as determined by X-ray photoelectron spectroscopy (XPS). Therefore, a two-step plasma treatment with two different specimen temperatures, i.e. 100°C followed by 45°C, decreased the water contact angle and reduced the aging effect. It appears that the hydrophilic functional groups introduced were located at the specimen surface (about 0.5 nm) at low temperature and that the aging effect was reduced due to the hydrophilic functional groups formed inside (0.5-8 nm) at high specimen temperature. The aging rate and the diffusion coefficient were also estimated, depending on the specimen temperature, using the experimental aging data.

Corona treatment improved bonding between sheets of cellulose and synthetic polymers. The bond strength increased at higher temperatures of pressing. Physical changes in the surface were detected microscopically after corona treatment in air. Sheets treated in pure nitrogen made strong bonds although the surface treated in nitrogen was indistinguishable from the untreated surface.

If a low-density polyethylene sheet is treated in a corona discharge and subsequently pressed to a similarly treated sheet at 45°C, the bond formed is much stronger than that between similarly pressed but untreated sheets. Several series of observations have indicated that this enhanced autohesion is not due to surface oxidation or to surface crosslinking (CASING). Evidence is presented that the effect may be related to some type of electret formation induced in the polymer sheet by the corona discharge.

Corona treatment of low-density polyethylene in oxygen or oxygen-containing gases produced bumps on the surface, while treatment in nitrogen, hydrogen, argon, or helium caused no detectable surface change. Bumps made by an oxygen corona increased in size with time and temperature of the treatment. The bumps were removed when a treated polymer sheet was dipped into solvents such as CCl₄, ethanol, or 0.2% aqueous NaOH. Infrared analysis indicated that most of the oxidized layer was eliminated from the polymer surface by solvent dipping and that the degraded products contained a substantial proportion of CH₂ groups. It is suggested that the bumps are caused by the migration of low molecular weight degradation products to charged areas of the polymer surface.

The hydrophobic recovery of polydimethylsiloxane elastomers was studied after exposure to partial electrical discharge. Silicone elastomers that were thoroughly extracted of free oligomeric impurities as well as those deliberately contaminated with low molecular weight (LMW) silicone fluids were used for these studies. Contact angle and X-ray photoelectron spectroscopy revealed that the recovery rates of the oxidized extracted samples are strongly influenced by the applied voltage, humidity, and aging condition. The recovery rates increase considerably as the applied voltage and the humidity during discharge increase. Remarkably, the oxidized samples stored under high vacuum (10⁻⁷ Torr) exhibit lower recovery rates than those aged in air. Free silicone fluid, when added to the elastomer, affects the recovery rate as well; however, significant recovery is seen even without any added fluid. These results imply that the LMW species that are formed in situ during electrical discharge are sufficient to cause the hydrophobic recovery of oxidized PDMS elastomers.

The surface characteristics of ethylene-vinyl acetate (EVA) were modified by argon, air, and oxygen plasma at atmospheric pressure. The surface energies of the EVA were evaluated by contact angles according to a sessile-drop method and adhesion energy (G(IC)) was estimated by a 180 degrees peel test with polyurethane (PU). After the plasma treatments, the surface free energies (or specific polar component) of the EVA increased about five times compared to that of virgin EVA. The adhesion between the EVA and the PU is significantly improved by the plasma treatment. Especially, Ar/air/O(2) plasma treatment increases G(IC) of EVA/PU up to about 600% compared to that of the sample using virgin EVA.

The molecular parameters of poly(vinyl alcohol) have enormous effects on its physical and chemical properties. Therefore, the surface characteristics of poly(vinyl alcohol) films are also determined by the molecular parameters. In this study, the dependence of the surface free energy on the molecular weight, degree of saponification, and stereoregularity of poly(vinyl alcohol) films has been evaluated with contact-angle measurements. The surface free energy of poly(vinyl alcohol) films increases with decreases in the syndiotactic dyad content, molecular weight, and degree of saponification. The polar component of the surface energy is not affected by the deviation of the molecular weight and degree of saponification very much. However, it decreases with increases in the syndiotactic dyad content and ranges from 11.64 to 4.35 dyn/cm.
© 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007 https://onlinelibrary.wiley.com/doi/abs/10.1002/app.26010

Although an adhesive joint can distribute load over a larger area than a mechanical joint, requires no holes, adds very little weight to structures and has superior fatigue resistance, it requires careful surface preparation of adherends for reliable joining and low susceptibility to service environments. The load transmission capability of adhesive joints can be improved by increasing the surface free energy of the adherends with suitable surface treatments. In this study, two types of surface treatment, namely the low pressure and the atmospheric pressure plasma treatment, were performed to enhance the mechanical load transmission capabilities of carbon/epoxy composite adhesive joints. The suitable surface treatment conditions for carbon/epoxy composite adhesive joints for both low and atmospheric pressure plasma systems were experimentally investigated with respect to chamber pressure, power intensity and surface treatment time by measuring the surface free energies of the specimens. The change in surface topography of carbon/epoxy composites was measured with AFM (Atomic Force Microscopy) and quantitative surface atomic concentrations were determined with XPS (X-ray Photoelectron Spectroscopy) to investigate the failure modes of composite adhesive joints with respect to surface treatment time. From the XPS investigation of carbon/epoxy composites, it was found that the ratio of oxygen concentration to carbon concentration for both low and atmospheric pressure plasma-treated carbon/epoxy composite surfaces was maximum after about 30 s treatment time, which corresponded with the maximum load transmission capability of the composite adhesive joint.

Asymmetric poly(vinyl alcohol) (PVA) membranes were prepared by the phase inversion technique, and crosslinked with glutaraldehyde. The degree of crosslinking of the membrane was controlled by varying the crosslinking conditions. The effects of the degree of crosslinking on the swelling characteristics, contact angles, critical surface tensions, and pervaporation characteristics were examined. A method for the evaluation of the degree of crosslinking, which needs only the gluaraldehyde concentration of the crosslinking solution to be measured after the crosslinking reaction, is proposed, and was found useful. The degree of swelling of PVA membrane for water decreases abruptly as the degree of crosslinking increases. However, the degree of swelling for ethanol is nearly independent of the degree of crosslinking. The critical surface tension of the membrane increases more or less within the range of 37.0–40.0 dyn cm⁻¹ with increasing degree of crosslinking below 30%. But, it is nearly constant at 40.5 dyn cm⁻¹ above 30%. The wetting behavior of the membrane may not be greatly affected by the degree of crosslinking. The selectivity factor and permeate flux of the membrane in the pervaporation of the ethanol-water mixture of 95 wt% ethanol concentration decrease similarly with increasing degree of crosslinking. The pervaporation characteristics seem to be closely related to the swelling behavior. The degree of crosslinking is an important variable for swelling behavior and pervaporation characteristics.

Oxygen plasma treatment was used to change the hydrophobic polysulfone ultrafiltration membrane to the hydrophilic membrane. The contact angle of water decreased with increasing the oxygen plasma treated time of polysulfone membrane and was saturated with 20 s of oxygen plasma treated time. Functional groups introduced by oxygen plasma treatment were examined using X-ray photoelectron spectroscopy (XPS) and zeta potential of oxygen plasma treated polysulfone membrane was measured using electrophoretic light scattering (ELS) spectrometer. O/C ratio increased from 33 to 50% and isoelectric point (IEP) of membrane surface increased from pH 3 to 4.5. For oxygen plasma treated polysulfone membrane, the flow rates of pure water and gelatin solution increased at all pH range and plasma treated membranes showed less fouling at membrane surface. The mechanisms of reduced fouling and improved cleaning efficiency of oxygen plasma treated polysulfone membrane were also studied.

Chemical etching, plasma, and ion beam treatments were used to modify the surface of Polytetrafluoroethylene (PTFE). Each surface treatment method developed different surface characteristics. In addition to morphological observation, contact angle, atomic chemical composition, and adhesion strength were measured after treatment with various methods. The different adhesion strengths were explained based on the morphology and atomic chemical composition of the treated PTFE surfaces. The chemical etching showed substantial defluorination, and the adhesion strength was fairly high. The argon plasma treatment introduced very large amounts of oxygen into the surface, and the surface was very smooth with a crater-like structure. Ion beam treatment induced a form of spires whose dimensions were of several micrometers, depending on the ion dose, whereas the oxygen plasma-treated samples showed short spires with spherical particles on the top. The spire-like surface morphology and increased surface area during bonding by ion beam treatment appear to be the reason for a higher adhesion strength than that of the oxygen plasma-treated PTFE. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1913–1920, 2000
https://onlinelibrary.wiley.com/doi/abs/10.1002/1097-4628%2820000829%2977%3A9%3C1913%3A%3AAID-APP7%3E3.0.CO%3B2-%23

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.

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.

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.

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.