The surface modification of high density polyethylene by a CO₂ microwave plasma is described with the aim of fixing carboxylic groups. The characterization is discussed in terms of functionalization, degradation, crystallization and cross-linking. The formation of carboxylic acids seems mainly favored by the presence of the CO₂ active species. The degradation leading via chain scissions to the formation of volatile byproducts is shown to be heterogeneous by mainly affecting amorphous zones. The structural modification is associated with a twisting motion of macromolecular chains having defects to more organized conformations. Finally, cross-linking appears weak due to the absence of chromophoric sites and of VUV radiations in the plasma.

Metallized polymer or polymer-based materials are used in a large range of electronics applications including the fabrication of ohmic contacts, chip-level interconnects, printed circuit boards and shielded materials.^1–7 For such technological applications, electroless deposition is the most widely used method in practice today.⁸ Basically, electroless plating is an autocatalytic redox process occurring in aqueous solution between ions of the metal to be deposited (generally Ni or Cu) and a strong reducer. Typical procedures involve a variety of multi-step sequences for the preparation of the surfaces to be coated. Conventionally, substrates are cleaned with solvents to remove surface contaminants, chemically etched to obtain a micro-roughened oxidized surface, and then seeded with a catalyst such as palladium. Chronologically, the seeding process was first accomplished by using a two-step procedure involving substrate treatment successively in dilute SnC1₂ (sensitization step) and PdC1₂ (activation step) acidic solutions. Further, a one-step procedure using a colloidal suspension containing both Sn and Pd species (a SnC1₂/PdC1₂ acidic solution) has been developed and is presently in common use in industrial environments. In this last case, the Pd/Sn colloidal particles adsorbed on the polymer surface must be exposed (acceleration step) to a solubilizer (a HCl or NaOH solution) to remove the excess of Sn⁺² species surrounding the catalytic Pd-based core of the colloidal particles. As can easily be inferred from the details of such multi-step procedures, it is today highly desirable to develop alternative approaches for making the insulating surfaces catalytically active. These approaches should require no chemical surface etching, reduce the number of process steps, and provide a highly selective, well-defined interaction between the catalytic species and the surface to be coated.⁹

The wet adhesion of water borne acrylic dispersions is a crucial factor on the performance of outdoor coatings on wood. Pine sapwood was treated with several methods for surface activation to increase the wet adhesion of water borne acrylic dispersions. The wet adhesion was measured by pull-off tests as well as with a modified cross-cut test. Atmospheric plasma, corona treatment and fluorination increased the wet adhesion of the coating which is attributed to the increasing polar portion of the surface free energy. Other ways of improving the wet adhesion are the addition of promotors, the use of primers and organisational improvements.

The rf power was modulated (discharge on-time of 10 μs and discharge off-time of 50–500 μs), for pulsed argon (Ar) and oxygen (O₂) plasmas used to irradiate PET film surfaces to modify the film surfaces. From data regarding the contact angle for the modified PET film surfaces and chemical analyses with XPS, effects of the rf power modulation on the surface modification are discussed. The pulsed Ar and O₂ plasmas are effective in modification of the PET film surface. There is no difference in the contact angle between the pulsed plasma and the continuous plasma. Furthermore, the pulsed Ar plasma is advantageous in formation of hydroxyl groups on the PET film surfaces. The rf power modulation has a possibility to modify into peculiar surfaces. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2845–2852, 2002
https://onlinelibrary.wiley.com/doi/abs/10.1002/app.10865

The changes of contact angle (θ) and surface free energy (γS) under low-temperature air plasma in the polymers of different chemical structure and polarity (polyethylene, PE; polypropylene, PP; poly(ethylene terephtalate), PET and poly(methyl methacrylate), PMMA) pointed out to the greater effect of short-time plasma action (5–15 s) on these parameters as compared to longer times of exposure.

The non-reversion effect of θ changes caused by plasma in PE and PP suggests that the oxidation processes mainly decide about values in nonpolar polymers. The significantly greater θ changes in PE than those in PP indicate that the side groups present in the main chains impede oxidation of such a polymer by plasma.

The reversion of θ changes in PET and in PMMA, and return of these values to almost the initial ones after 10 min storage proves that the main reason for θ changes in polar polymers is a certain alteration of the chain conformation.

These changes, taking place after longer plasma treatment, suggest that the side ester groups in PMMA retard the above-mentioned conformational transformations. Then, in both kinds of polymers (polar and nonpolar) the structure of macrochain decides about the efficiency of reaction caused by plasma, and at the same time the side groups retard not only the oxidation processes but the conformational changes as well.

Novel types of non-thermal plasma sources at atmospheric pressure based on multi-pin DC (direct current) diffusive glow discharge and AC (alternative current) streamer barrier corona have been elaborated and tested successfully for cold surface treatment of polymer films [polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET),] and polyester fabric. Results on physical properties ofdischarges mentioned and output energy characteristics of new plasma sources as well as data on after-treatment changes in wettability of films and fabrics are presented. The main goal of this study was to find out the experimental conditions for gas discharge and surface processing to achieve a remarkable wettability change for a short treatment time.

The liquid state of matter plays a very important role in everyday life, and the liquid surface has a dominant role in many phenomena. In fact, about 70% of the surface of Earth is covered by water. The most fundamental characteristic of liquid surfaces is that they tend to contract to the smallest surface area to achieve the lowest free energy. Whereas gases have no definite shape or volume, completely filling a vessel of any size containing them, liquids have no definite shape but do have a definite volume, which means that a portion of the liquid takes the shape of that part of a vessel containing it and occupies a definite volume, with the free surface plane except for capillary effects where it is in contact with the vessel. This is evident in rain drops and soap films, in addition to many other systems that will be mentioned later. The cohesion forces present in liquids and solids and the condensation of vapors to liquid state indicate the presence of much larger intermolecular forces than the gravity forces. Furthermore, the dynamics of molecules at interfaces are important in a variety of areas, such as biochemistry, electrochemistry, and chromatography. The degree of sharpness of a liquid surface has been the subject of much discussion in the literature.

The surface energies of poly (methyl methacrylate), polycarbonate and poly (tetrafluoroethylene) which have been exposed to UV radiation in an ambient ozone-air atmosphere have been elucidated from surface tension and contact angle data using these test liquids: ethylene glycol, formamide, glycerol, methylene iodide and water. Comparisons of surface energy values obtained using Kaelble’s two-liquid method, Good’s three-liquid method and Neumann’s macroscopic apнproach are reported. It is tentatively suggested that atmospheric moisture may play a role in producнing discordant values since the test liquids ethylene glycol, formamide and glycerol are highly hyнgroscopic in nature. It has been demonstrated that UV/ozone irradiation produces changes in surface roughness. Poly (tetrafluoroethylene) shows three distinct regions: first, where at low irradiation times the surface roughness is enhanced and following this, the roughness decreases before increasнing finally to a terminal value. The behavior is somewhat similar for polycarbonate although the dramatic increase in roughness exhibited by poly (tetrafluoroethylene) is absent. The roughness characteristics are quite different for poly (methyl methacrylate) where a large change in roughness is observed at only one specific irradiation time. Thus presently it is not possible to predict surface roughness changes for a particular polymer and more studies on the morphological changes occurнring at different surfaces are being carried out.

The behavior of a silicone sealant during its application, from its extrusion from the carнtridge to the completion of the joint, has been identified as a key feature for professional applicators. This feature called “ease of use’* is very complex and includes many different criteria such as the ease of extrusion and joint smoothing, the aesthetic of surface finish, the stringing, and the action of a tooling aid (aqueous solution of surfactant) during the smoothing operation. Several of these criteнria seem directly linked to surface properties of the uncured sealant. In an attempt to translate these subjective properties into quantitative measurements in the laboratory and to understand the underнlying parameters that can be used to control these features, the surface energy of uncured sealants was measured using the solid-liquid contact angle technique. The surface energy data were further correlated with ratings collected from professional applicators with regards to ease-of-use criteria. A correlation was also built between the contact angle values obtained with various tooling aid soluнtions against the surface of the sealant and the ease of smoothing obtained by using these tooling aids at the application stage. The evolution of the contact angle of a water droplet at the surface of uncured sealant with time provided some insights in the understanding of the migration and/or reнorientation of polar entities from the sealant bulk to the sealant surface.

The objective of this study was to determine the surface free energy components of celнlulose ethers films. The surface free energy parameters were calculated from the contact angles of sessile drops of apolar and polar liquids on cellulose ether films cast on glass slides using the Lifshitz-van der Waals/acid-base (LW/AB) approach according to the method of van Oss, Chaudhury and Good (Chem. Rev. 88, 927-941, 1988). The cellulose ethers studied were hydroxypropyl methylcellulose (HPMC), methylcellulose (MC), hydroxypropylcellulose (HPC) and hydroxyethylcellulose (HEC) and ethylcellulose (EC). The total surface free energy of these cellulose ethers ranged from 29-50 mJ/m2. The overall trend in the values of the thermodynamic terms derived from the surface free energy parameters as indicators of hydrophilicity was in good agreement with the relaнtive bulk solubility and hydration behavior of the polymers. Calculation of the work of adhesion with substrates of varying surface free energy parameters indicated that acid-base interactions made a major contribution to the total work of adhesion between cellulose ethers and bipolar surfaces. Changes in surface free energy as a result of the presence of plasticizer or change in solvent compoнsition for EC films were resolvable with the LW/AB approach. Although no direct correlation could be established between the surface free energy parameters and the type of substitution on the celluнlose backbone for the cellulose ethers, the values of the terms derived from the LW/AB approach were consistent with those of cellulose. The LW/AB approach provides a reasonably consistent method for estimating the surface properties of cellulose ethers and the resulting surface free energy parameters are shown to relate to the interfacial properties of the polymers.

Recently receding contact angles have increasingly attracted attention in studies of wetting phenomena. The difference between the advancing and receding contact angles of the same liqнid on the same solid surface is termed 'contact angle hysteresis'. The hysteresis is usually ascribed to the solid surface roughness and/or its chemical heterogeneity. These possible mechanisms of the hysteresis appearance do not exclude another interpretation of the receding contact angle origin (E. Chibowski et al., in: Surfactants in Solution, A.K. Chattopadhyay and K.L. Mittal (Eds.), pp. 31-53, Marcel Dekker, 1996). In this approach, the presence of liquid film behind the drop is considered to be the cause for the ovbserved hysteresis, except, of course, for cases of rough and/or macro-chemically heterogeneous solid surfaces. In this paper, a new approach is presented and then verified using experimental advancing and receding contact angles taken from the literature. This approach allows an evaluation of the total surface free energy of a solid if the advancing and receding contact angles for a probe liquid are known. It does not require values of the solid surface free energy components for estimation of the value of total surface free energy.

The two methods used for contact angle determination in this study are based on liquid porosimetry (LP). The LP measures volumes of different size pores when the liquid advances and then when the liquid drains from a porous structure. The LP provides pore volume distribution (PVD) and numerous other pore structure characteristics. The experimental data for this study were obtained with an automated TRI/Autoporosimeterо. The first method for contact angle measurement uses two liquids. One liquid has a known contact angle with the sample solid and the second is the liquid of interest. A comparison of the capillary pressures in different size pores for the two liquids provides the contact angle data for different size pores in the sample.

The effects of 1, 2, 3, 4-tetrahydronaphthalene (tetralin) solvent and ammonia plasma treatments on surface characteristics and adhesion of ultra-high-strength polyethylene (UHSPE) fiнbers to epoxy resin were studied. Spectra™ 1000 (UHSPE) fibers were treated with either tetralin solvent or in combination with ammonia plasma, under various conditions. The changes in the fiber surface topography were characterized using scanning electron microscopy (SEM). Dynamic wetнtability measurements were made using the Wilhelmy technique. The fiber/epoxy resin interfacial shear strength (IFSS) was evaluated by the single fiber pull-out test. The fiber surfaces after the pull-out test were characterized by SEM. The SEM photomicrographs and wettability data showed that the surface roughness of the fibers increased after the tetralin solvent treatment and the fiber surface became more polar after the ammonia plasma treatment. The IFSS results indicated that combined tetralin and ammonia plasma treatments resulted in significant improvement in the adheнsion strength of UHSPE fibers with epoxy resin. This is attributed to the chemical, mechanical and topographical changes of the fibers resulting from the treatments.

The acid-base theory of surfaces, as proposed by van Oss, Chaudhury and Good, comнmonly suffers from a series of problems (apparent too high basicity of surfaces, results depending on the choice of liquid triplets, etc.). These problems can be solved if and only if a great attention is paid to the mathematical properties of the equations on which the theory is based. Two of these problems are analysed in detail in the present paper: the choice of the acid-base scale using water as a reference, and the use of the 'equilibrium' contact angle instead of the adнvancing contact angle.

The common measurement of the contact angle is performed in conditions not corresponding to true equilibrium states and gives non-equilibrium values, the advancing and receding contact angles. To solve this problem, a very simple experimental device, based on the Wilhelmy experiment, is proposed in the present paper. It is able to transfer mechanical energy to the three-phase system in a controlled way through a simple loudspeaker; the analysis of some common surfaces is made through this method showing as a new stable minimum of the surface free energy can be attained, independent on the initial conditions and corresponding to a value of the contact angle intermediate between the advancing and receding ones. A comparison is developed with literature results on heterogeneous and rough surfaces, some ‘first-order’-approximation equations proposed in the literature are examined and compared with the new results. A simple but useful theoretical treatment is also compared with the experimental results to allow a more detailed, although qualitative-level, analysis. An important consequence with respect to the calculations of solid surface free energies is indicated.

Electrons produced in atmospheric pressure corona discharges are used for a variety of beneficial purposes including the destruction of gaseous contaminants, and surface treatment. In other applications, such as electrostatic precipitators and photocopiers, unintended reactions such as ozone production and deposition of silicon dioxide are detrimental. In both situations, a kinetic description of the electron distribution in the corona plasma is required to quantify the chemical processes. In this paper, the electron density and energy distributions are numerically determined for a positive dc corona discharge along a wire. The electron density distribution is obtained from the 1-D charge carrier continuity equations and Maxwell's equation. The non-Maxwellian electron kinetic energy distribution is determined from the Boltzmann equation. The effects of wire size (10-1000 μm) and current density (0.1–100 μA/cm of wire) on number density and energy distribution of electrons are presented. With increasing current, the electron density increases, but the thickness of the plasma and the electron energy distribution are not affected. Smaller electrodes produce thinner plasmas and fewer, but more energetic electrons, than larger wires. The effect of electrode size on the electron-impact chemical reaction rate is illustrated by the rates of dissociation and ionization of oxygen and nitrogen.

High density polyethylene sheets 2 mm thick were flame treated to modify the surface properties. Sheets treated using a flame with air to gas (methane) ratio ∼ 10:1 at different distances between the inner cone tip of the flame and the polymer surface were investigated. Grafting of selected monomers as maleic anhydride, acrylamide and glycidyl methacrylate was attempted by flame treatment of sheets covered with a monomer layer. Good grafting results were obtained with acrylamide and maleic anhydride. The surface temperature-time dependence during the flame treatment was measured with a high resolution thermocouple. Scanning Electron Microscopy (SEM) allowed evidencing a modified thickness of about 120 μ. The chemical surface modification was studied by X ray Photoelectron Spectroscopy (XPS) and Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFT). The hydroxyl, carbonyl and carboxyl content was measured after derivatization with reagents containing an elemental tag to facilitate XPS analysis of surface functional groups. In comparison to the untreated polyethylene, wetting tension and contact angle of the flamed materials showed a strong variation. This variation was almost independent of the distance between the flame and the polymer surface. Adhesion between treated polyethylene and a polyurethane adhesive was determined using T-peel test measurements. High adhesion levels were found with flame treated polyethylene at 5 mm distance. XPS results indicate that when adhesion is high, the hydroxyl is in excess compared to the other measured functions, i.e. carbonyl and carboxyl species.

The surface of polyether ether ketone (PEEK) films was modified using plasma treatment, corona, or surface etching to improve their adhesion with regard to glued copper foils and copper layers generated by physical vapor deposition. After the pretreatments, surface chemical analysis was performed by X-ray photoelectron spectroscopy (XPS). The wetting behavior was qualitatively investigated by contact angle measurements. Surface topography was monitored by laser scanning microscopy (LSM). After coating, the adhesion strength of the copper layer was measured by a peel force test. Plasma treatment, corona discharge, or etching lead to a significant increase in adhesion. This increase is caused by a change in surface topography as well as by the incorporation of polar groups into the surface.