Lifshitz-van Der Waals Component Research Articles

Work of adhesion and activity of aqueous solutions of ternary mixtures of hydrocarbon and fluorocarbon nonionic surfactants at the water–air and polymer–water interfaces

The values of the surface tension and contact angle on the polytetrafluoroethylene surface (PTFE) of aqueous solutions of the ternary mixtures of hydrocarbon surfactants, TX100 and TX165, and fluorocarbon FSN100 at different mole fractions of surfactants in the bulk phase were applied for the studies of the correlation between the adsorption of surfactants at the solution–air and polymer–solution interfaces, the work of adhesion determined from the Young–Dupree equation, the parameter of the intermolecular interactions and the spreading coefficient of aqueous solutions of the studied mixtures on the PTFE surface. For this purpose the values of the total mole fraction and activity of surfactants at the polymer–solution interface obtained from the Sprow and Prausnitz equation were compared to those at the solution–air one. Also on the basis of the mole fraction of the particular surfactants at the PTFE–solution and water–air interface and on the assumption of the additivity of the adhesion work, the work of adhesion of the fluorocarbon tail to the PTFE surface as well as the Lifshitz–van der Waals component of the PTFE surface tension were calculated.

Passivation of High-Surface-Energy Sites of Milled Ibuprofen Crystals via Dry Coating for Reduced Cohesion and Improved Flowability

Ibuprofen micronization with dry coating is investigated to examine its influence on passivation/stabilization of high-surface-energy sites and reduced cohesion. A fluid energy mill was used to micronize ibuprofen particles down to 5-28 μm with or without simultaneous nanosilica coating. Powder flow property and dispersibility were characterized using FT4 powder tester and Rodos/Helos laser diffraction particle sizer. Surface energy was characterized using a next generation inverse gas chromatography instrument. Uncoated micronized ibuprofen showed an increased Lifshitz-van der Waals (LW) dispersion component of surface energy with increasing milling intensity. In contrast, dry-coated milled powders showed a significant reduction in the LW component, whereas physical mixture of uncoated micronized ibuprofen and silica exhibited no reduction in surface energy, indicating that dry coating is necessary for the passivation of high-energy sites of ibuprofen created during micronization. Surface energy of pure micronized ibuprofen was highly heterogeneous, whereas dry-coated ibuprofen had greatly reduced heterogeneity. Micronization with dry coating also improved flowability and bulk density as compared with pure active pharmaceutical ingredient micronization without coating, or just blending with silica. Overall, dry coating leads to decreased cohesion and improved flowability because of reduced LW dispersive component of surface energy and creating nanoscale surface roughness.

Effect of chemical modification on surface free energy components of Aerosil silica powders determined with capillary rise technique

Abstract The knowledge about interfacial energy interactions and surface free energy is necessary for understanding and modeling many surface and interface processes. The aim of this paper is to study the effect of the chemical modification on the surface free energy components of Aerosil OX50. This fumed silica is chemically modified using the hydrophobic organosilane hexadecyltrichlorosilane (HTS). The modification process is studied by Fourier transform infrared spectroscopy (FTIR) and total carbon mass measurements performed on solid silica samples. The combination of these two techniques allows the determination of the adsorption isotherm of HTS onto silica showing the formation of a plateau for an initial concentration of 3 mM. The quantity adsorbed of HTS at maximum coverage is 2.14 μmol/m 2 . However, the chemical modification does not elaborate a compact layer. The HTS density is approximately 1.2 molecules/nm 2 which is close to the density of hydroxyl groups on the surface. A recent method, developed by Chibowski and Perea-Carpio, based on imbibition of probe liquids into a thin porous layer (capillary rise), is used for the determination of the surface free energy components. The surface free energy γ s decreases continuously from 54.2 mJ/m 2 for bare silica to 46.7 mJ/m 2 for silica treated at an initial concentration of 4 mM following a linear diminution of γ s with the HTS adsorbed amount. The apolar Lifshitz-van der Waals component γ s LW is reduced from 41.1 mJ/m 2 to 35.8 mJ/m 2 . The electron-donor parameter γ s − drops from 53.9 mJ/m 2 to 27.5 mJ/m 2 while the electron-acceptor parameter γ s + remains roughly constant (1 mJ/m 2 ). Trends in the surface free energy components are notably linked to observations in infrared spectra and give additional information about the structure of the HTS layer.

Surface free energy analysis of adsorbents used for radioiodine adsorption

In this work, the surface free energy of biomass-based activated carbons, both fresh and impregnated with triethylenediamine, has been evaluated. The contribution of Lifshitz van der Waals components was determined by the model proposed by van Oss et al. The results obtained allowed predicting the most probable configurations of the impregnant onto the carbon surface and its influence on the subsequent adsorption of radioactive methyl iodide.

Surface energy characterization of carbonate rocks

Carbonate rocks (calcite and dolomite) account for more than half of the world's hydrocarbon reserves. Despite the complexity posed by these rocks, it is important to understand the fundamental forces of adhesion responsible for the spreading and distribution of reservoir fluids, such as crude oil/brine on the reservoir rock surface. These physico-chemical interactions determine the surface energetics of a reservoir and affect their wetting characteristics. Inverse gas chromatography is introduced to characterize the surface energy of carbonates (calcite and dolomite). The behavior of the polar and non-polar interaction forces was investigated at varying water coverage and at different temperatures. The results indicated that in general as the water coverage increased, the Lifshitz–van der Waals component of surface energy decreased to nearly that of the bulk water, while the acid–base component also showed a decreasing trend. The Lifshitz–van der Waals component of surface energy always decreased with increase in temperature, while the acid–base properties showed contrasting trends for the two minerals.

Surface energy characterization of sandstone rocks

The fundamental forces of adhesion are responsible for the spreading of fluids such as crude oil/brine on the reservoir rock surface. These physico–chemical interactions determine the surface energetics of a reservoir and thus their wetting phenomena. Inverse Gas Chromatography (IGC) is introduced to characterize the surface energy of sandstones (Ottawa sand and Berea sandstone). The surface chemistry of the sandstone rocks is further elucidated using X-ray diffraction (XRD) and X-ray Photoelectron Spectroscopy (XPS) techniques. The behavior of the polar and non-polar interaction forces was investigated at varying water coverage and at different temperatures. The results indicated that in general as the water coverage increased, the Lifshitz–van der Waals component of surface energy decreased to nearly that of the bulk water, while the acid–base component also showed a decreasing trend. The Lifshitz–van der Waals component of surface energy always decreased with increase in temperature, while the acid–base properties showed contrasting trends in line with changes in surface chemistry of the sandstones, due to the change in temperature. Finally, the wetting properties arising in reservoir sandstones were related to the surface chemistry of the reservoir fluids and their interactions with the reservoir rock surface.

Surface Tension of Polytetrafluoroethylene and Polymethyl Methacrylate under the Influence of the Fluorocarbon Surfactant Film

Measurements of the contact angle for water, formamide, and diiodomethane on polytetrafluoroethylene (PTFE) and polymethyl methacrylate (PMMA) covered by Zonyl FSN-100 (FSN100) and Zonyl FSO-100 (FSO100) films were made. On the basis of the obtained values, the Lifshitz–van der Waals component and electron-acceptor and electron-donor parameters of the acid–base component of PTFE and PMMA covered by the surfactant film surface tension were determined by the use of van Oss et al. approach to the interfacial tension and Young’s equation. The components and parameters of surface tension were discussed in the light of the sorption of fluorocarbon surfactants at the polymer/solution interface and proper orientation of the surfactant molecules to this interface. Taking into account the changes of determined values of the components and parameters of PTFE and PMMA surface tension under influence of the surfactant films, the relationship between the adhesion tension and the surface tension, as well as between the cosine of contact angle and the surface tension of aqueous solution of fluorocarbon surfactants, was explained.

Wettability, adhesion, adsorption and interface tension in the polymer/surfactant aqueous solution system. I. Critical surface tension of polymer wetting and its surface tension

The contact angle of aqueous solutions of Triton X-100, Triton X-114, Triton X-165, sodium dodecylsulfate, sodium hexadecylsulfonate, cetyltrimethylammonium bromide, cetylpyridinium bromide, sodium N-lauryl sarcosinate, dodecyldimethyethylammonium bromide, tetradecyltrimethylammonium bromide and benzyldimethyldodecylammonium bromide on polytetrafluoroethylene, polymethyl methacrylate and nylon 6 was studied. The contact angle values were used in the Young equation for the polymer–solution interface tension calculation and for the determination of the critical surface tension of polymer wetting. The critical surface tension of polymer wetting was obtained on the basis of the relationship between the cosine of contact angle and/or the adhesion tension as a function of the surface tension of aqueous solution of studied surfactants and then was discussed in relation to the Lifshitz–van der Waals components and electron-acceptor and electron-donor parameters of polytetrafluoroethylene, polymethyl methacrylate and nylon 6 surface tension. The role of the parameter of interfacial interactions in the relationship between the critical surface tension of polymer wetting and the surface tension was also considered. This parameter was calculated by using the polymer–solution interface tension as well as the polymer and aqueous solutions of surfactant surface tension.

In vivo measurement of the surface energy of human fingernail plates

The surface energy of the human nail plate is expected to influence the adhesion of microorganisms (and subsequent colonization and infections) as well as that of medicines (and subsequent drug permeation) and of cosmetics. The aim of the study was therefore to measure the surface energy of nail plates in vivo. The surface energy of healthy human fingernails (untreated, hydrated and abraded) and of hoof membranes (often used as a model for the nail plate) was estimated from contact angle measurements of liquids (water, formamide, diiodomethane and glycerol) on the nail plate and subsequent computation using the Lifshitz-van der Waals/acid-base (LW-AB) approach. The surface energy of untreated fingernail plates was found to be 34 mJ m(-2) . Most of this total energy was from the apolar Lifshitz-van der Waals component. When the polar component of the surface energy was analysed, the electron donor component was considerably larger than the electron acceptor one. Hydrating the nail plate had no significant influence on the surface energy. In contrast, abrasion caused a small, but statistically significant increase in the apolar surface energy component. The surface energy of bovine hoof membrane was similar to that of the fingernail plate. We conclude that the human fingernail plate is a low-energy surface and that bovine hoof membranes may be used as a substitute for the nail plate in certain experiments.

Relationship Between Interfacial Shear Strength and Interfacial Tension of Silicone/Quartz Glass Fiber Composites

In this paper, the surface tension components of three silicone resins were determined with an advanced contact angle technique, which was composed of dynamic cycling contact angle and axisymmetric drop shape analysis (ADSA). The interfacial properties of three silicone/quartz glass fiber composites were measured through interfacial shear strength (IFSS) testing experiment. It was found that the Lifshitz–van der Waals component was the main surface tension component for all of the silicones. There is a perfect linear relationship between the interfacial tension and the IFSS. With the increase of the Lifshitz-van der Waals component, the interfacial tension and the IFSS of composites increased. Therefore, the Lifshitz-van der Waals component is the most important parameter for explaining the interfacial shear property of silicone/glass fiber composites.

Insights into bacterial contact angles: Difficulties in defining hydrophobicity and surface Gibbs energy

One of the principal techniques for evaluating the surface hydrophobicity of biological samples is contact angle. This method, applied readily to flat-smooth-inert surfaces, gives rise to an important debate when implemented with microbial lawns. After its initial description, in 1984, several authors have carried out modifications of the technique but the results obtained have not been previously judged. This work focuses on the particularities of contact angle measurements on bacterial lawns and enhances the idea of the impossibility of using water contact angle as a universal measurement of bacterial hydrophobicity. Contact angles can only be used as relative indicators of hydrophobicity, in a similar way to tests based on microbial adhesion to solvents. The strong dependence of contact angles on dried bacterial lawns with measuring time and environmental conditions (e.g. pH of the media) preclude the estimation of their absolute values, and so, of the cells surface Gibbs energy. Yet, for a given measuring time, it is found that the hydrophobicity and the apparent bacterial surface Gibbs energy components are qualitatively related to the bacterial surface electrical potential. In particular, a hydrophobic increase is always accompanied by an increase of the cells Lifshitz-Van der Waals component and a decrease of their acid-base component and absolute zeta potential. Therefore, the present study shows that the physico-chemical surface properties that characterize bacteria are not independent, and one of them can be qualitatively described in terms of the others when measuring contact angles at a fixed time after the drying of the microbial beds.

Cold flame-sprayed and oil-impregnated porous metallic coatings

Porous metallic coatings were prepared from three commercial alloy powders on 16MnCr5 steel by cold flame spraying. The mechanical characterisation of the coatings was performed by Vickers microindentation and debonding tests. Porosity was determined by image analysis of the optical micrographs of the polished cross-sections. The coatings were impregnated with motor oil 15W40 with the aim of preparing a lubricating system. The amounts of oil uptake and release by the coatings were determined under controlled conditions. The surfaces of the coatings were examined by X-ray photoelectron spectroscopy (XPS) and wettability studies. The amounts of oil uptake and release showed inverse relationship with the oxygen concentration at the surface and also with the Lifshitz-van der Waals component of surface energy. These relationships offer the possibility of controlling the lubrication properties of cold flame-sprayed and oil-impregnated porous metallic coatings.

Surface energetics of bone mineral and synthetic hydroxyapatite using inverse gas chromatography

Surface energy is one of the important factors that govern protein adhesion and cell attachment on biomaterial surfaces. Inverse gas chromatography (IGC) provides an excellent method to measure the surface energetics of rough and porous biosurfaces. In this study IGC was used to characterize and compare the surface energetics of synthetic and biological hydroxyapatites (natural bone mineral). IGC experiments were performed on three samples: synthetic hydroxyapatites with two levels of purity (99% and 90%) and natural biological hydroxyapatite obtained from bovine trabecular bone. The Lifshitz–Van der Waals component of the surface free energy ( γ S L W ) and specific interaction parameter ( ɛ π) were determined by using homologous series of n-alkanes and alkenes as IGC probe molecules, respectively. The synthetic hydroxyapatite had values of γ S L W of 33.4 mJ m −2 at 99% purity and 53.3 mJ m −2 at 90% purity. Biological hydroxyapatite had a value of γ S L W of 45.7 mJ m −2. For the synthetic hydroxyapatite, the values of π-bond specific interaction parameters, ɛ π, were 0.95 mJ (99%) and 3.01 mJ (90%). The biological hydroxyapatite sample had a value of 2.44 mJ for ɛ π. The results suggest that, as compared to the synthetic compounds, the biological apatite has considerable surface heterogeneity, either chemical (impurities) or structural suggesting a scaffold surface that is more conducive of protein adhesion and cell attachment.

The wettability of polytetrafluoroethylene and polymethylmethacrylate with regard to interface behaviour of Triton X-165 and short chain alcohol mixtures: I. Critical surface tension of wetting and adhesion work

Wetting of polymers (PTFE, PMMA) by aqueous solutions of Triton X-165 mixtures with methanol, ethanol and propanol was studied in a wide range of alcohol and Triton X-165 concentration. The Triton X-165 concentration range corresponded to its unsaturated and saturated monolayer in the absence of alcohol. The wetting properties of Triton X-165 and alcohol mixtures were determined on the basis of advancing contact angles measurements by the sessile drop method. From the obtained contact angle values the relationships between cos θ, the adhesion tension and surface tension of the solutions, cos θ and the reciprocal of the surface tension were determined. On the basis of these relationships the correlation between the critical surface tension of PTFE and PMMA wetting and the surface tension of these polymers and work of adhesion of aqueous solution of TX-165 and alcohols mixtures to PTFE and PMMA surface was discussed. The critical surface tension of PTFE wetting was found to be close to its surface tension determined from the contact angles for polar liquids, but the critical surface tension of PMMA wetting considerably lower than its surface tension and even the Lifshitz–van der Waals components of this surface tension.

Behavior of cationic surfactants and short-chain alcohols in mixed surface layers at water–air and polymer–water interfaces with regard to polymer wettability: II. Wettability of polymers

The wettability of polytetrafluoroethylene (PTFE) and polymethylmethacrylate (PMMA) by aqueous solutions of cetyltrimethylammonium bromide (CTAB) mixtures with short-chain alcohols such as methanol, ethanol, and propanol, as well as for 1-hexadecylpyridinium bromide (CPyB) with the same alcohols, was studied on the basis of advancing contact-angle measurements by the sessile drop method over a wide range of alcohol and cationic surfactant concentrations where they can be present in solution in monomeric or aggregated form. It should be noted that the contact angles for aqueous solution mixtures of cationic surfactants with propanol on PTFE surfaces were measured earlier and presented in our previous paper. From the obtained contact-angle values the relationships between cos θ and surface tension of the solutions ( γ LV ) and that between adhesion tension and γ LV were considered. The relationship between the cos θ and the reciprocal of γ LV was also discussed. From these relationships the critical surface tension of PTFE and PMMA wetting and the correlation between the adsorption of cationic surfactant and alcohol mixtures at water–air and polymer–water interfaces were deduced. On the basis of the contact angles and components and parameters of the surface tension of surfactants, alcohols, and polymers also the Gibbs and Guggenheim–Adam isotherm of adsorption and the effective concentration of alcohols and surfactants at polymer–water interfaces were calculated. Next, the work of adhesion of solution to polymer surface with regard to the surface monolayer composition was discussed. The analysis of the contact angles with regard to adsorption of surfactants and alcohols at polymer–water and water–air interfaces allowed us to conclude that the PTFE wetting depends only on the contribution of the acid–base interactions to the surface tension of aqueous solutions of cationic surfactant and alcohol mixtures, and the adhesion work of solution to its surface only slightly depends on the concentration and composition of solution, in contrast to PMMA. The critical surface tension of PTFE wetting is close to its surface tension determined for liquids in which the surface tension is two times or more higher than that of PTFE, but for PMMA it is considerably lower than its surface tension and even the Lifshitz–van der Waals component of this tension.

Comparison of Surface Tension Components and Hansen Solubility Parameters Theories. Part I: Explanation of Protein Adsorption on Polymers

Surface tension components and Hansen solubility parameters are two different theories used to explain and predict the compatibility and miscibility for polymer blends, composite polymer materials, and additives in polymer matrix. In this paper, the adsorption mechanism of bovine serum albumin (BSA) on eight polymers (PC, POM, PBT, PPO, PSF, PVDF, PEI, and PES) was researched through surface tension components and Hansen solubility parameters theories. The adsorption amounts of BSA on the polymers were measured through static adsorption experiments. It was found that the BSA adsorption amount cannot be directly correlated with the Hansen solubility parameters. However, there is high correlation between the Lifshitz-van der Waals component of surface tension of the polymers and BSA adsorption amount. With the increase in van der Waals value, the BSA adsorption amount on the polymers increases, but there still exists a complicated behavior. The protein adsorption mechanism is complex.

Correlation between surface free energy of quartz and its wettability by aqueous solutions of nonionic, anionic and cationic surfactants

The measurements of the advancing contact angle for water, glycerol, diiodomethane and aqueous solutions of Triton X-100 (TX-100), Triton X-165 (TX-165), sodium dodecyl sulfate (SDDS), sodium hexadecyl sulfonate (SHDS), cetyltrimethylammonium bromide (CTAB) and cetylpyridinium bromide (CPyB) on quartz surface were carried out. On the basis of the contact angles values obtained for water, glycerol and diiodomethane the values of the Lifshitz–van der Waals component and electron-acceptor and electron-donor parameters of the acid–base component of the surface free energy of quartz were determined. The determined components and parameters of the quartz surface free energy were used for interpretation of the influence of nonionic, anionic and cationic surfactants on the wettability of the quartz. From obtained results it was appeared that the wettability of quartz by nonionic and anionic surfactants practically does not depend on the surfactants concentration in the range corresponding to their unsaturated monolayer at water–air interface and that there is linear dependence between adhesional and surface tension of aqueous solution of these surfactants. This dependence for TX-100, TX-165, SDDS and SHDS can be expressed by lines which slopes are positive. This slope and components of quartz surface free energy indicate that the interaction between the water molecules and quartz surface might be stronger than those between the quartz and surfactants molecules. So, the surface excess of surfactants concentration at the quartz–water interface is probably negative, and the possibility of surfactants to adsorb at the quartz/water film–water interface is higher than at the quartz–water interface. This conclusion is confirmed by the values of the adhesion work of “pure” surfactants, aqueous solutions of surfactants and water to quartz surface. In the case of the cationic surfactants the relationship between adhesional and surface tension is more complicated than that for nonionic and anionic surfactants and indicates that the relationship between the adsorption of the cationic surfactant at water–air and quartz–water interface depends on the concentration of the surfactants in the bulk phase.

The wettability of polytetrafluoroethylene and polymethylmethacrylate by aqueous solutions of Triton X-100 and short chain alcohol mixtures

Measurements of advancing contact angles ( θ) were carried out for aqueous solutions of Triton X-100 (TX-100) and methanol and ethanol mixtures at constant TX-100 concentration equal to 1 × 10 −7, 1 × 10 −6, 1 × 10 −5, 1 × 10 −4, 6 × 10 −4 and 1 × 10 −3 M, respectively, on polytetrafluoroethylene (PTFE) and polymethylmethacrylate (PMMA). Using measured contact angle values the relationships between cos θ, adhesion tension and surface tension of the solutions were determined, and on their basis the critical surface tension of PTFE and PMMA wetting was calculated. The obtained average value of the critical surface tension of PTFE wetting is lying in the range of the PTFE surface tension values which can be found in the literature, while for PMMA it is even lower than the Lifshitz–van der Waals component of its surface tension. From the relationship between the adhesion and surface tension and Lucassen–Reynders equation it results that in the case of PTFE the adsorption at the PTFE–solution and solution–air interfaces is the same, which was confirmed by a linear relationship between the cos θ and 1/ γ LV and intercept on cos θ axis equal to −1. However, for PMMA the adsorption of the surface active agents at solution–air interface is higher than at PMMA–solution. Using the values of the contact angle the values of the adhesion work of solution to the PTFE and PMMA surface were also determined, which are constant for PTFE, but for PMMA decrease with alcohol concentration increase. Next, using the contact angle values in the Young equation, the PTFE(PMMA)–solution interface tension was also calculated. The obtained values of PTFE–solution interface tension were compared with those evaluated from the Szyszkowski, Connors and Fainerman and Miller equations, and good agreement between these values was observed for all series of TX-100 and alcohol mixtures at a low alcohol concentration.

Effects of environmental conditions on fluorinated diamond-like carbon tribology

The effects of environmental conditions and fluorine content on friction of diamond-like carbon (DLC) films are determined and discussed. Relative humidity (RH) has a considerable effect on friction values, modifying them up to a factor 2. Two regions of RH are found, depending on its effect over friction. From 20% to 60% of RH, friction decreases probably due to a better substitution of superficial atoms by hydrogen. From 60% to 80% friction remains stable and equal for almost all samples. A possible explanation would be the formation of a physisorbed layer of water on the surface, which would mask the relatively small chemical and structural variations of the films. Moreover, the different components of surface free energy (SFE) are determined using Van Oss–Chaudury–Good model. The results clearly indicate the importance of Lifshitz–Van der Waals component on SFE and the small correction that supposes acid-base interactions. According to this model, the studied DLC is a monopolar basic material. The basic component is reduced when F content is increased.

Plasma treatment of heat treated beech wood – investigation on surface free energy

With an increased interest in finding alternatives for tropical timbers and preservative-treated wood, several new wood treatments have recently been commercialised, e.g., acetylation, furfurylation and heat treatment. For the latter, diverse techniques protected by trademarks have been developed, such as the Plato process, retification process, oil-heat treatment, thermo wood and Stellac treatment, whereby the chemical and physical properties of the treated wood are altered (Boonstra et al. 2006a,b). Beneficial changes are the improved dimensional stability and durability which, among other reasons, are caused by the loss of hydroxyl groups which results in reduced hygroscopicity and increased hydrophobicity of surfaces (Tjeerdsma and Militz 2005; Petric et al. 2007). On the other hand, wettability is a prerequisite for good adhesion, but it is reduced by less hydrophilic surfaces after heat treatment. Accordingly, the deposition of waterborne finishes is generally more difficult on heat treated wood (Petrissans et al. 2003; Geradin et al. 2007). Polymer processing industries are using plasma treatment techniques to improve wettability and adhesion on hydrophobic polymer surfaces (Kogelschatz 2003). By plasma treatment, the O/C ratio is increased by the formation of hydroxyl and carboxyl groups which brings about an increase in surface polarity (Jie-Rong et al. 1999; Drnovska et al. 2003) and may be able to compensate partly the loss of functional groups by heat treatment. Several publications deal with plasma treatment of wood or wooden materials for hydrophilicity increment: elevated surface free energy and an ameliorated wetting behaviour with water were found (Rehn and Viol 2003; Rehn et al. 2003; Evans et al. 2007; Toth et al. 2007; Wolkenhauer et al. 2007a,b,c). In general, air, nitrogen or oxygen are the gaseous media to increase hydrophilicity; however, plasma techniques can also be applied for this purpose, i.e., to decrease hydrophilicity. For example, in the presence of special chemicals or reactive gases (e.g., HMDSO, silane) thin layers can be deposited on wood surfaces for creating water repellent characteristics (Denes et al. 1999; Bente et al. 2004; Odraskova et al. 2007). Podgorski et al. (2000) investigated the wetting behaviour of water on heat treated wood after application of oxygen plasma treatment at low pressure (0.08 mbar) and found a significant decrease of water contact angles. To explore the surface modification by plasma treatment in more detail, the surface free energy and the work of adhesion based on the Lifshitz-van der Waals/acidbase approach were determined (Van Oss et al. 1988). In this approach, the total surface energy is divided into (1) a polar or acid-base component, and (2) a dispersive or Lifshitz-van der Waals component. The polar part is further subdivided into an acid part (electron acceptor) and a basic part (electron donor) with regard to the Lewis acid-base model. The latter includes hydrogen bonding, whereas the disperse part or the Lifshitz-van der Waals part comprises London, Keesom and Debye interactions. In the present study, a dielectric barrier discharge (DBD) was used for plasma treatment of heat treated wood. DBD was performed at atmospheric pressure and ambient air to avoid the impact of low pressure.