Glow discharge plasma is an effective method for treating surfaces, sputtering, etching, plasma-assisted deposition, ashing, and is used in a range of other processes. Sigma Technologies Int’l, Inc., has developed a novel plasma system which can be operated at atmospheric pressure, thereby eliminating the need for vacuum chambers and pumps. This atmospheric plasma system can be effectively used for surface treatment and for plasma-assisted deposition. This plasma system has been tested successfully for the functionalization of various polymer films. The surface energies of the films treated by the newly developed atmospheric plasma system have been shown to increase substantially, thereby enhancing the wettability and adhesion properties of these films. Details of the atmospheric pressure plasma system, and the results from treatment tests are presented.

Critical surface tension (CST) is a measure of solid surface tension and is mainly determined by measuring the contact angle of a droplet on a target solid surface. The concept of CST makes it possible to determine solid surface tension without any unprovable assumptions such as the Fowkes hypothesis. However, it requires somewhat special devices and skills for measuring the contact angle. In this work, we propose a simple method to determine the CST of a solid by measuring the droplet spreading area. This method is developed by combining the conventional CST with a simple analytical droplet model. The difference in estimated CSTs between our method and the conventional one is within 3.0%. Our method enables a quick and simple evaluation of the solid surface tension without special devices for measuring the contact angle.

Poly(tetrafluoroethylene) (PTFE) samples were surface modified in gas plasma atmospheres of air, oxygen, argon and water vapour in order to increase the surface energy. Its dispersive and polar components were determined by contact angle measurements after various treatment times. Plasma treatment times of only 15s were sufficient in all gases studied for substantial surface modification of PTFE. The chemical composition of the surfaces was studied by X-ray photoelectron spectroscopy (X.p.s.). The main results of all the plasma treatments were the abstraction of fluorine and the production of surface crosslinks, whereas only a low level of oxygen-containing groups was attached into the surface layer.

Hypothesis: Both the surface free energy (γ) and solubility (δ) parameters of substances are related to their cohesive energies which are decided by intermolecular interactions, and there should be some intrinsic relationships between the two parameters. Understanding of the γ-δ correlations is of great fundamental and practical importance. Several empirical γ-δ equations have been proposed so far, but their application to solids is limited. This is because the molar volume (V~) as a parameter exists in these equations while the V~ of solids is commonly hard to be obtained. Hence, the development of γ-δ equations without the parameter V~ is essential for solids.

Method: The γ and δ data of 21 solids including polymers and layered solid materials were chosen, and possible γ-δ relationships were systematically explored using the parameter data of solids by a trial and error fitting method.

Finding: Six γ-δ equations without the parameter V~ are proposed. The γ parameters include total (γ_t), dispersive (γ_d), and polar (γ_p) ones, and the δ parameters include the Hildebrand parameter (δ_t) and the Hansen dispersive (δ_d), polar (δ_p), and hydrogen-bonding (δ_h) ones. Interestingly, the so-obtained V~-free γ-δ equations are also valid for most liquids including nonpolar and polar ones. These γ-δ equations can provide a way to estimate non-measurable parameters from measurable parameters for solid materials, which is beneficial to the application of the characteristic parameters (γ and δ) for solid material engineering.

The characterization of polymer-water interfaces by contact angle measurement is performed using water-immiscible liquids. It gives the dispersive and the nondispersive components of surface free energy as a function of functional group of copolymer hydrogels. Using the method of Rusanov, the contactangle-induced deformation of the three-phase region in our systems was examined. The systems used were poly(2-hydroxyethyl methacrylate) (HEMA), poly(2-hydroxyethyl methacrylate-methyl methacrylate) (HEMA-MMA), poly(2-hydroxyethyl methacrylate-methoxyethoxyethyl methacrylate) (HEMA-MEEMA), poly(2-hydroxyethyl methacrylate-aminoethyl methacrylate) (HEMA-AEMA), and poly(2-hydroxyethyl methacrylate-diethylaminocthyl methacrylate) (HEMA-DEAMA). The deviation of contact angle due to the surface deformation was found to be appreciable in case of poly(HEMA-AEMA) and poly(HEMA-DEAMA).

Contact angle measurements on polymer hydrogels were performed at various temperatures, and we obtained the dispersive (γ_s^d) and nondispersive (γ_s^p) components of the surface tension of polymer hydrogel at each temperature. Utilizing the temperature dependence values of γ_s^d and γ_s^p, we obtained the surface entropies of polymer hydrogels. The polymer hydrogels used were isotactic and syndiotactic poly(2-hydroxyethyl methacrylate) (HEMA), poly(2-hydroxyethyl methacrylate + aminoethyl methacrylate) (HEMA + AEMA), poly(2-hydroxyethyl methacrylate + N-vinyl pyrrolidone) (HEMA + VP), poly(2-hydroxyethyl methacrylate + methyl methacrylate) (HEMA + MMA), poly(2-hydroxyethyl methacrylate + methoxyethyl methacrylate) (HEMA + MEMA), and poly(2-hydroxyethyl methacrylate + methoxyethoxyethyl methacrylate) (HEMA + MEEMA), respectively. The contact angles were also measured by using droplets of water-immiscible liquids under conditions in which the polymer hydrogel was fully hydrated.

Oxygen plasma-treated quenched and annealed polypropylene (PP) films with different crystallinities were investigated to characterize the surface rearrangement behavior during aging using contact-angle measurements and X-ray photoelectron spectroscopy. Optimum plasma conditions were examined by varying the power, time and pressure. Less crystalline quenched PP showed a larger increase in water contact angle and a larger decrease of oxygen atomic concentration during aging than the more crystalline annealed PP, since the oxygen species, such as hydroxyl groups, introduced by oxygen plasma treatment, oriented towards or diffused faster into the bulk with lower crystallinity. The degree of crosslinking on the surface was enhanced after plasma treatment and, in addition to increased crystallinity, the crosslinked structure induced by plasma treatment restricted chain mobility and lowered the aging rate of the PP surface.

Injection-molded samples of polypropylene were exposed to oxygen plasma and SACO (SAndblasting and COating) treatments. The pretreated surfaces were successively adhesively bonded or lacquered. The adhesion strength and failure mode of these specimens were examined. The surfaces obtained after treatments were characterized by electron spectroscopy for chemical analysis (ESCA), contact angle measurements, and scanning electron microscopy (SEM). Both microroughness and chemical modification of the surface led to an increase in adhesion by up to a factor of 10. The stability of the surface changes generated during the plasma and SACO pretreatments was observed by different kinds of aging experiments in air and water. The aging of SACO-treated surfaces led to no significant change on the surface. In the case of plasma-treated surfaces, hydrophobic recovery during aging in air reduced the polarity of the surface layer. During aging in water, no hydrophobic recovery on the surface was observed.

The surface characteristics of polymers are important factors determining their interfacial properties and their technological performance. Changes in physical and chemical properties of a polymer film may be induced by subjecting the material to a variety of surface modification techniques, one of which is ion-beam modification. In order to understand the underlying mechanisms X-ray photoelectron spectroscopy (XPS) was used to study the alterations of the polystyrene (PS) surface after Ar-ion treatment under well controlled conditions with low ion doses from 10¹² to 10¹⁶ cm^-2. The ion bombardment leads to surface functionalization, loss of aromaticity, and free radical formation. Induced surface cross-linking and the formation of polar groups raised the surface glass transition temperature of PS film.

Ultrahigh molecular weight polyethylene (UHMWPE) fibers were treated using pulsed KrF (248 nm) excimer laser in air and in diethylenetriamine (DETA), to improve their adhesion to epoxy resin. The effects of fluence, number of pulses and the treatment environment were explored. Topographical and chemical changes on the fiber surface were characterized using several techniques, including X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), atomic force microscopy (AFM) and dynamic wettability measurements. SEM micrographs and AFM images revealed that the surface roughness of fibers increased after the laser treatment and was a function of the fluence (energy density) of the laser beam and number of pulses. The XPS data indicated that oxygen and nitrogen were incorporated on the fiber surfaces making them more polar. The dynamic wettability data confirmed the presence of polar groups on the fiber surfaces. The UHMWPE fiber/epoxy resin interfacial shear strength (IFSS) increased by up to 600% for some treatment conditions. Introduction of polar groups and increased surface roughness are two main factors that contribute to the increased adhesion (IFSS) of the UHMWPE fiber/epoxy resin system significantly.

Ultra-high-molecular-weight polyethylene (UHMWPE) fibers (Spectra® 1000) were treated using pulsed XeCl excimer laser (308 nm) to improve their adhesion to epoxy resin. The la-ser treatments were carried out in air and in diethylenetriamine (DETA) environments with varying numbers of pulses and fluences. The effects of the laser treatments on the fiber surface topography, chemistry and wettability were investigated. The interfacial shear strength (IFSS) with epoxy resin was measured using a single fiber pull-out test. The surface roughness was characterized using scanning electron microscopy (SEM) and atomic force microscopy (AF M). The laser treatment introduced grooves along the fiber length and increased the fiber surface roughness up to 6-times the control value, as measured by AFM. The X-ray photoelectron spectroscopy (XPS) data indicated that oxygen and/or nitrogen were incorporated on the fiber surface afier the laser treatments depending on the environment in which the treatments were carried out. For some treatments the oxygen/carbon ratio increased by up to 2.5-times the control value. The dynamic wettability data showed that the laser treatments significantly increased the acid-base component of the surface energy and the work of adhesion. The UHMWPE fiber/epoxy resin IFSS increased by up to 400% for certain treatment conditions. The introduction of polar groups and higher surface roughness were found to be the two main factors that contributed to the significant increase in the adhesion of the UHMWPE fiber/epoxy resin system.

Effects of the electron radiation generated by a high-voltage linear accelerator on wettability and surface free energy (SFE) of low-density polyethylene (PE-LD) film were studied. Radiation doses of 25, 50, 100, 250, and500 kGy were used. Water, glycerol, formamide, diiodomethane, and α-bromonaphthalene were applied as measuring liquids for contact angle measurements. The calculations of SFE were made by Owens-Wendt and van Oss-Chaudhury-Good methods, using the results of measurements of contact angle with various systems of the measuring liquids. Wettability tests were also performed. It was found that the contact angle decreased with the rising radiation dose for all the measuring liquids and the shapes of these dependences were similar. However, significant quantitative differences were observed. The largest changes in the contact angle were detected for the dose range of up to 50 kGy. SFE values when measured by different methods and various measuring liquids differed generally in the whole range of the doses applied. Therefore, the surface free energy cannot be accepted as an absolute measure of the thermodynamic state of the surface layer of radiation-modified PE-LD film. Its values can be compared with one another only when they were determined using the same method and the same measuring or standard liquids.

The physical and chemical principles of the process of polymeric material surface layer (WW) modification using corona discharge (WK) in an air were discussed. The phenomenon of low temperature plasma formation and the way of its interaction with polymer surface were described. Basic aims of the process of modification with WK were presented as well as the results obtained this way for particular polymers, among others PE, PP, PVC, PET. In case of PE and PP also the composite materials with polyolefine matrix or fiber filler were considered. The possibilities of corona discharge use in graft polymerization were noticed. Also numerous directions of practical use of the changes of polymers' surface layers caused by corona discharge were marked.

A new method of analysis of differences in the surface free energy (SFE) values of a solid, calculated using the methods of Owens-Wendt (OW) and Neumann and two measuring liquids, water and diiodomethane, is presented. The concept of the analysis bases on the differences in SFE, which occur objectively and regardless of both the precision and the performing conditions of the contact angle (CA) measurements. These differences result from utilizing of different mathematical relations between CA and SFE in each of the methods. The results obtained with these two methods are compared with one another over the SFE range common for polymeric materials (20-50 mJ/m 2). It is calculated that the relative difference in SFE between the results from the OW and Neumann methods can reach 19.9 % over this range.

In the article the analysis of the main methods of calculations of interfacial free energy and surface free energy (SEP) values of solids, in which contact angle measurements' results play a key role, has been presented. The importance of Young's equation and Berthelot's hypothesis as the scientific basis of these methods has been indicated. Various methods of calculations of interfacial free energy values for solid-liquid systems, including calculations of this energy on the basis of state equations or SEP divide to independent components, (especially for polymers) were discussed. The most important methods of calculations of SEP values for polymeric materials on this basis were characterized. The methods of calculations of contact angle values for porous materials, granulated products, powders or fibers on the basis of Washburn equation, what is a base for calculations of SEP of these materials, were presented.

A review covering the general objectives of surface modification of plastics articles with particular reference to the flame modification technique. Hydrocarbon combustion conditions and flame modification parameters are described. Flame modification effects exercised on various, mostly polyolefinic, products are synthetically analyzed. The flame technique is shown to be advantageous and complementary to the corona-discharge technique. The effects of the polypropylene modification conditions on the oxygen content, the wetting angle for water, the free surface energy and the resistance of adhesion bonds are described.

Several methods for the determination of both the surface free energy of polymer materials and the conditions necessary to perform contact angle measurements are discussed. The effects of the corona-treatment energy on the surface free energy and on the adhesion of acrylic adhesive were studied using a biaxially-oriented polypropylene film. The surface free energy was determined by the Owens-Wendt, and van Oss-Chaudhury-Good approaches, as well as with the wettability method, using different liquids. The presented results confirm that the surface free energy value depended on both the method used and the nature of probe liquids. Thus, it cannot be considered as a parameter characterizing unambiguously the surface layer of a corona-treated film. The values of the surface free energy for different film samples can be compared with one another only if determined using the same method and the same liquids. The variations of particular components of the surface free energy with the corona-treatment energy depend on e.g. the nature of probe liquids, which makes interpretation of the observed effects difficult.

The results of an X-ray photoelectron spectroscopic investigation of the oxidation of surface layers of low-density polyethylene (LDPE) and biaxially oriented polypropylene (BOPP) films are presented. The analysis was performed using different take-off angles, namely 10°, 30°, and 90°; thus, the depths of the examined layers were 0.6, 1.9, and 3.7 nm, respectively. It was found that the course of the oxidation process in the surface layers was similar for both polymer films. However, for treatment energies lower than 5 kJ/m², the extent of the oxidation was higher for the LDPE film, whereas for energies above this value, the BOPP film was more oxidized. As detected by X-ray photoelectron spectroscopy (XPS), desorption of oxygen from the film surface occurs for both polymers during the treatment.

The effects of the unit corona-treatment energy on the contact angle of various liquids, on the surface free energy, on the extent of oxidation of a surface layer, and on the adhesion of acrylic adhesive were studied using a biaxially-oriented polypropylene (BOPP) film. The surface free energy was determined with the van Oss-Chaudhury-Good (VCG) approach as well as with the wettability method. The extent of oxidation of the surface layer of the corona-treated BOPP film was evaluated with X-ray photoelectron spectroscopy. The adhesion strength of joints between the BOPP film and the acrylic adhesive was measured using the 180°

In the range of the unit corona-treatment energy up to 1.2 kJ/m², a rapid increase in the surface free energy with the treatment energy is observed. In the range above that value, the surface free energy rises relatively slowly. The extent of oxidation of the surface layer and the adhesion strength of joints between the BOPP film and the acrylic adhesive are approximately in direct proportion to the unit energy of the corona treatment. A five-fold growth of the adhesion strength of the studied joints within the examined range of the treatment energy was found.In the range of the unit corona-treatment energy up to 1.2 kJ/m², a rapid increase in the surface free energy with the treatment energy is observed. In the range above that value, the surface free energy rises relatively slowly. The extent of oxidation of the surface layer and the adhesion strength of joints between the BOPP film and the acrylic adhesive are approximately in direct proportion to the unit energy of the corona treatment. A five-fold growth of the adhesion strength of the studied joints within the examined range of the treatment energy was found.In the range of the unit corona-treatment energy up to 1.2 kJ/m², a rapid increase in the surface free energy with the treatment energy is observed. In the range above that value, the surface free energy rises relatively slowly. The extent of oxidation of the surface layer and the adhesion strength of joints between the BOPP film and the acrylic adhesive are approximately in direct proportion to the unit energy of the corona treatment. A five-fold growth of the adhesion strength of the studied joints within the examined range of the treatment energy was found.

The selected problems related to investigations of surface layers (WW) of solids were presented. The analysis of essential limits of van Oss - Chaunhury - Good's (vOCG) method, used for calculation of surface free energy (SEP) of polymeric materials, has been done. Some reasons of discrepancy between the results of calculations, obtained by various authors, were discussed in details. Namely, the need of use of algebraic analysis for selection of the set of three measured liquids, which are necessary in vOCG method, has been pointed. It makes possible to eliminate the sets of liquids being the reasons of bad conditioning of the sets of equations for SEP calculation. The effect of the proper selection of scale of components (acidic and basic ones) of SEP of water on the right evaluation of selected properties of the materials investigated was also presented (Table 1&2). General conclusions concerning the causes of controversy over van Oss - Chaunhury - Good's method were formulated.

Effect of the electron radiation generated by a high-voltage linear accelerator on the wettability, contact angle and surface free energy (SFE) of a biaxially oriented polypropylene (BOPP) film was studied. Radiation doses of 25, 50, 100, 250, and 500kGy were used. Water, glycerol, formamide, diiodomethane, and α-bromonaphthalene were applied as measuring liquids. The calculations of SFE were made with the methods of Owens–Wendt and van Oss–Chaudhury–Good, using the results of measurements of the contact angle with various sets of the measuring liquids. Wettability tests were also performed. It was found that the contact angle decreased with the rising radiation dose for all the measuring liquids and the shapes of these dependences were similar to one another. However, significant quantitative differences were observed. The largest changes in the contact angle were detected in the dose range of up to 100kGy. The SFE values when measured with different methods and various measuring liquids differed generally in the whole range of the applied doses. Therefore, the surface free energy cannot be accepted as an absolute measure of the thermodynamic state of the surface layer of a radiation-modified BOPP film. Its values can be compared with one another only when they were determined with the same method and same measuring or standard liquids.

Influence of the unit energy (E_u) of corona discharge used for modification of pure polylactide (PLA) and polylactide nanocomposite (PLAC) containing 5 wt% of an aluminosilicate nanofiller (Cloisite 30B) on water (Θ_W) and diiodomethane (Θ_D) contact angles as well as on surface free energy (γ_s) of these polymers was studied. Θ_W and Θ_D as advancing contact angles were measured with use of a goniometer while γ_s was calculated by the Owens–Wendt method. It was found that Θ_W increased with the rising E_u while Θ_D remained approximately constant. Assuming E_u = const, it could be stated that the increase in γ_s was much more evident for PLA than for PLAC. This increase resulted practically from the change in the polar component of γ_s because the dispersive component for the two materials only slightly decreased with increase in E_u.