The experimental work reported here is devoted to the electrical study of two atmospheric pressure dielectric barrier discharge (DBD) reactors operating at high gas flow, conceived for surface treatment applications in spatial afterglow conditions. Both reactors are of coaxial geometry with the dielectric covering the active electrode, and are driven by a power generator delivering quasi-sinusoidal voltage waveforms in the 100–160 kHz range. The influence of the gas flow value and of the input power on the electrical operation of these systems is investigated. The comparative study performed here, by means of electrical measurements, reveals the influence of parameters such as geometrical dimensions and dielectric material used on the operation of the DBD. Power factor measurements are used to quantify the reactors' electrical performance. Optical diagnostics and kinetic modelling reveal a high chemical activity of the systems appropriate for the treatment of surfaces at atmospheric pressure.

PTFE surface modifications have been realized using low-pressure RFGD, DBD and APGD in different atmospheres. Compared to the RFGD NH₃ plasma, the DBDs operating in H₂/N₂ lead to similar surface concentrations of amino groups and similar surface damage, but with a much higher specificity. Both APGDs in H₂/N₂ and NH₃/N₂ lead to lower concentrations of amino groups, but with similar specificity, and with lower surface damage than the RFGD treatment. A method is proposed to evaluate the efficiency of the different discharges for amine surface functionalization of PTFE, and it is concluded that the NH₃/N₂ APGD discharge is the one that give the best results for an effective surface treatment.

Atomic-force microscopy was used to study structural chemical transformations on the surface of polyvinyl chloride films subjected to modification with compounds based on acrylic acid derivatives, with preliminary activation of the polymer surface with a corona discharge.

Polyolefin surfaces, namely isotactic poly(propylene) (iPP) and low-density polyethylene (LDPE), were modified by corona discharge plasma. The chemical changes on the modified surfaces were observed, deeply affecting the surface and the adhesive properties of the studied materials. The hydrophobic recovery in the case of iPP is considerably dependent on the polymer crystallinity. The presence of the processing agents in the LDPE has a significant influence on the surface hydrophobization dynamics.

In this work, low pressure glow discharge O₂ plasma has been used to increase wettability in a LDPE film in order to improve adhesion properties and make it useful for technical applications. Surface energy values have been estimated using contact angle measurements for different exposure times and different test liquids. In addition, plasma-treated samples have been subjected to an aging process to determine the durability of the plasma treatment. Characterization of the surface changes due to the plasma treatment has been carried out by means of Fourier transformed infrared spectroscopy (FTIR) to determine the presence of polar species such as carbonyl, carboxyl and hydroxyl groups. In addition to this, atomic force microscopy (AFM) analysis has been used to evaluate changes in surface morphology and roughness. Furthermore, and considering the semicrystalline nature of the LDPE film, a calorimetric study using differential scanning calorimetry (DSC) has been carried out to determine changes in crystallinity and degradation temperatures induced by the plasma treatment. The results show that low pressure O₂ plasma improves wettability in LDPE films and no significant changes can be observed at longer exposure times. Nevertheless, we can observe that short exposure times to low pressure O₂ plasma promote the formation of some polar species on the exposed surface and longer exposure times cause slight abrasion on LDPE films as observed by the little increase in surface roughness.

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.

Ammonia plasma treatments were performed on both thermoplastic plates and fabrics made of poly (ethylene terephthalate)(PET). The plates became more hydrophilic with improved adhesion properties as expected, whereas the fabrics became more hydrophobic, yet positively charged. Plasma treatments of PET fabrics using gas mixtures such as NH3/N2 and HZ/NZ were performed in order to simulate pure ammonia plasma treatments since such treatments are not always applicable in industrial applications, due to environmental and safety reasons. It was shown that the recommended and allowed gas compositions, 15% NH; in N2 and 5% H2 in N2, did not show any similarity with pure ammonia plasma treatments with respect to surface charge, wettability and chemical surface composition. At least 80% NH; in N; or 80% H2 in N2 is needed to simulate an ammonia-like plasma treatment of PET fabrics.

An understanding of the surface free energy and surface chemistry of solids is needed for investigation into the nature of processes involving adhesion, wetting and liquid penetration. Frequently the contact angles of several probe liquids on a given solid are used for calculation of solid surface free energy. Models by Fowkes, Kwok and Neumann, van Oss, Chaudhury and Good, as well as by Chang and Chen have been used for such calculations. Each of the above models has been championed in the literature. It has been noted by the present author and others that the use of different models may lead to different qualitative interpretations of the nature of a solid surface. A disinterested comparison of the various available models has not been made. In the present paper, a comparison of the calculations is undertaken in order to better understand the limitations of each model. Particular attention to the assumptions required for contact-angle data to be used for surface free energy calculations is given. The effect of the degree to which the experimental contact-angle data meet the required assumptions have on the calculated surface free energy is addressed in this work. When data meeting the theoretical assumptions common to the various published models are used, all of the published models fit the data, to a good approximation, equally well. A poor fit of the experimental data is an indicator that at least one liquid does not fully meet the assumptions re-quired by the chosen model. Differences in the acid—base character of the solid surface appear to re-sult from the acid—base scale used by the model. The paper is intended to raise the awareness of the difficulties in assigning surface free energy and predicting wetting behavior.

The measurement of contact angles and, thus, determination of solid surface tension has been considered for years as a “comedy of errors”, but in recent years the introduction of more sophisticated techniques and of computer-controlled devices, along with a general better understanding of surface structures, has led to a greater precision and accuracy of measurements. However, it is common to neglect the difference between the advancing contact angle and the Young’s angle or to underestimate the role and significance of receding contact angles. In previous papers an experimental procedure has been developed, called the Vibration Induced Equilibrium Contact Angle (VIECA), applied to a Wilhelmy experiment, which appeared to be able to provide a really stable and equilibrium-like value: this procedure was based on previous, rare literature attempts at providing an operational and satisfactory definition of equilibrium contact angle. The VIECA results seem to be related to the advancing and receding values through simple, but approximate, relations. Moreover, the VIECA appears to be independent of the roughness and heterogeneity of the surfaces analysed in the majority of cases. In the present paper, the VIECA method is extended to the sessile drop technique and comparison is made with the common advancing or “static” estimates of contact angle. A theoretical modelling of the physical situation induced by the application of mechanical vibrations to the meniscus or to the drop is proposed. The main consequence of these results is that the contact angles on common surfaces for common liquids are overestimated; a more subtle consequence is the effect on the evaluation of the surface free energy via the most common semiempirical models.

The essential form of an initially straight wetting triple line perturbed by the presence of a (higher surface free energy)“defect” on the solid surface has been recognised for a long time, and it corresponds to a logarithmically decaying form. However, less attention has been paid to the behaviour of the triple line within the domain of the defect. This was actually studied a few years ago from a theoretical viewpoint, leading to the prediction of an inversion of curvature. Recent experimental work has been concerned with the electrochemical treatment of PTFE, leading to small etched areas of higher wettability with typical widths of 100-300 um. Wetting experiments have been carried out on such solids and the results confirm the general conclusion of inverted curvature of the triple line in the treated zones. However, the “excess wettability” in the treated zones, as evaluated experimentally, was found to be greater than predicted theoretically. Possible causes are discussed.

An experimental study of the constant velocity displacement of various water/glycerol solutions by air in poly (vinyl chloride)(PVC) capillary tubes is reported. This topic is of particular interest in relation to dewetting processes on surfaces covered by a liquid film. More specifically, variations of the dynamic contact angle with velocity and their relation to the physicochemical properties of the systems studied are investigated. These results and those of other authors are analyzed in the framework of both hydrodynamical and molecular approaches of the dynamic contact-angle problem. These comparisons indicate that either the molecular or the viscous dissipation mechanism may be dominant, depending on the system studied. These results are used to suggest explanations for apparent discrepancies between dewetting velocity measurements in different systems previously reported by the authors.

We summarize here a mean-field representation of fluid free-energy to a lattice Boltzmann scheme recently proposed for interfacial studies. The interfacial behaviors obtained from this new multi-phase lattice Boltzmann model (LBM) were validated by means of the Laplace equation of capillarity and the capillary wave dispersion relation. Applications of this mean-field LBM to various interfacial studies are reviewed, including wettability on heterogeneous surfaces, self-propelled drop movement, contact line dynamics and solid–liquid interfacial slip. The mean-field LBM simulates systems with better physical reality in terms of solid–liquid interactions and could be an alternative for simulating interfacial phenomena.

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.

A view of contact angle hysteresis from the perspectives of the three-phase contact line and of the kinetics of contact line motion is given. Arguments are made that advancing and receding are discrete events that have different activation energies. That hysteresis can be quantified as an activation energy by the changes in interfacial area is argued. That this is an appropriate way of viewing hysteresis is demonstrated with examples.

A recent study has illustrated a sizeable increase in the printing characteristics of nonwovens following atmospheric plasma treatments. The improvement of properties such as wettability, printability and adhesion opens up new application prospects for treated fabrics.