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.

Polyamide 6, polyamide 12, polybutyleneterephthalate, and polyetherimide films are plasma treated in an APGD unit using various applied voltages, gas flow rates, frequencies, and dwell times. The results show changes in the surface chemistry (FTIR); the degree of change in dynamic contact angle is found to be dependent on the polymer type, dwell time, and electrical characteristics of the plasma.

Air plasma treatment at low pressure was applied to modify the surface of a cellulose film with the aim to improve its wettability, dyeability and adhesion properties. The contact angles of different polar liquids on the treated films show an exponential decay with treatment time at a given power; the power–time reciprocity is followed. The calculated surface tension values exponentially rise to the same maximum value with a decrease of the polar fraction. ATR-FTIR analyses suggest that a cellulose dehydration takes place rather than a surface oxidation. The plasma treatment improves also the cellophane dyeability with typical dyes for cellulose fibers: the results of dye uptake follow the same trend as the surface energy. The bond strength of lap joints of cellophane with LLDPE film shows a strong improvement of the adhesion depending on the duration and the power of treatment. The whole results are consistent with ablation effects like those observed with air corona treatment rather than oxygen plasma.

In the absence of weak boundary layers, surface energy can be an excellent indicator of the suitability of a fiber-reinforced composite surface for adhesive bonding. Mechanical surface treatments such as grit blasting are effective and commonly used to prepare composite surfaces, but the roughness introduced by these treatments makes quantification of the surface energy by contact angle methods difficult. This paper shows that the diameter of a small drop of a low-viscosity fluid chosen to have surface tension characteristics very similar to the adhesive can be used as an effective predictor of adhesive bond fracture energy. This technique could form the basis of a sensitive quality assurance tool for manufacturing.

Polyacrylonitrile fibers were treated with a nitrogen glow-discharge plasma. The surfaces of untreated and treated fibers were examined with contact angle measurements, atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). Surface energy calculations of the fibers were carried out from contact angle measurements using the relationships developed by Fowkes. It is found that plasma treatment causes a reduction in water contact angle on the fiber surfaces. The dispersion component of surface energy changes slightly, while the polar component is increased significantly from 14.6 mN/m to 58.7 mN/m and the total surface energy increase is 139%. The increase of surface energy is mainly caused by the introduction of hydrophilic groups on the fiber surfaces after plasma treatment.

Surface properties of polycarbonate (PC), polypropylene (PP), polyethylene terephthalate (PET) samples treated by microwave-induced argon plasma have been studied with contact angle measurement, X-ray photoelectron spectroscopy (XPS) and scanned electron microscopy (SEM). It is found that plasma treatment modified the surfaces both in composition and roughness. Modification of composition makes polymer surfaces tend to be highly hydrophilic, which mainly depended on the increase of ratio of oxygen-containing group as same as other papers reported. And this experiment further revealed that CO bond is the key factor to the improvement of the hydrophilicity of polymer surfaces. Our SEM observation on PET shown that the roughness of the surface has also been improved in micron scale and it has influence on the surface hydrophilicity.

The effect of air dielectric barrier discharge plasma treatment on the chemical structure and morphology of polypropylene (PP)film was studied using UV-VIS (ultraviolet-visible),FT-IR,(Fourier transform infrared),SEM (scanning electron microscopy)and AFM (atomic force microscopy).Polypropylene samples were printed using solvent-based gravure ink.An evaluation of the print quality criteria of the treated PP films included measurement of print density and print gloss.SEM investigated the ink laydown on the modified PP film.The results showed that after a few seconds of plasma treatment,both the surface energy and the surface roughness of the treated PP film increased.There was an increase in the absorbance at the almost-visible range,and C=C and C=O bands were found after the air discharge plasma treatment.A short plasma treatment of 15 seconds was found to bring about a dramatic increase in the print density readings,but a decrease in print gloss.The time of the air discharge plasma treatment was found to have no effect on the print density or print gloss at a high ink film thickness.The results showed that air dielectric barrier discharge plasma treatment,for a few seconds,is effective in printing and is economical for industrial use (this will be studied in detail in future work).

In an attempt to modify the hydrophobic surface properties of polypropylene (PP) films, this study examined the optimum process parameters of atmospheric pressure plasma (APP) using Ar gas. Under optimized conditions, the effects of a mixed gas (Ar/O2) plasma treatment on the surface-free energy of a PP film were investigated as a function of the O2 content. The polar contribution of the surface-free energy of the PP film increased with increasing O2 content in the gas mixture. However, slightly more oxygen-containing polar functional groups such as CO, CO, and COO were introduced on the PP film surface by the Ar gas only rather than by the Ar/O2 gas mixture. In addition, AFM analysis showed that the Ar plasma treatment of the PP film produced the smoothest surface as a result of the relatively homogeneous etching process.

The article describes applications of a novel windowless argon excimer source for surface modification. Experimental results on etching of polymeric surfaces, degradation of organic surface residues, surface activation and modification of gas permeability and selectivity of polymeric membranes are presented. Moreover, radical formation from the excimer source and surface curing of liquid acrylates are examined. Typical treatment times are in the range of minutes for photolytic decomposition effects and seconds for UV curing effects. The surface modification effects induced by the argon excimer source were analysed by XPS, ESR, IR-spectroscopy, white light reflection spectroscopy, scanning electron microscopy, micro-hardness and permeation measurements.

The decrease in the corona treatment effect with time and its influence on the flexographic printability of low-density polyethylene-coated paperboard were studied. After corona treatment, sheets were stored in different ways. Some sheets were stored in a laboratory atmosphere, while others were protected from exposure to light, air, moisture and dust in polyethylene bags. The tendency for ink to spread on the surfaces was studied using contact angle measurements. Printability was evaluated as print density, dot gain, uncovered (white) and mottling. The results obtained show that the surface energy of the protected sheets decreased with time, but not as much and not as quickly as that of the unprotected sheets. In the case of the protected sheets, the percentage uncovered areas and mottling remained constant, but for the unprotected sheets they increased with increasing time after the corona treatment. No significant differences were seen in the other print quality measures. Copyright © 2005 John Wiley & Sons, Ltd.
https://onlinelibrary.wiley.com/doi/abs/10.1002/pts.708