A RECENT communication by Gray¹ illustrates a possible pitfall in the use of the theories of Fowkes^2–5 and Good and Girifalco^6,7 to estimate surface energies, and the various components of surface energy, from contact angles. This source of error is the incorrect identification of the surface tension terms, and the equating of the contact angle in a contaminated, experimental system to that in a system composed of properly pure components. Thus, Gray wrote Fowkes's equation in the form

Wetting, the process of water interacting with a surface, is critical in our everyday lives and in many biological and technological systems. The contact angle is the angle at the interface where water, air and solid meet, and its value is a measure of how likely the surface is to be wetted by the water. Low contact-angle values demonstrate a tendency of the water to spread and adhere to the surface, whereas high contact-angle values show the surface’s tendency to repel water. The most common method for surface-wetting characterization is sessile-drop goniometry, due to its simplicity. The method determines the contact angle from the shape of the droplet and can be applied to a wide variety of materials, from biological surfaces to polymers, metals, ceramics, minerals and so on. The apparent simplicity of the method is misleading, however, and obtaining meaningful results requires minimization of random and systematic errors. This article provides a protocol for performing reliable and reproducible measurements of the advancing contact angle (ACA) and the receding contact angle (RCA) by slowly increasing and reducing the volume of a probe drop, respectively. One pair of ACA and RCA measurements takes ~15–20 min to complete, whereas the whole protocol with repeat measurements may take ~1–2 h. This protocol focuses on using water as a probe liquid, and advice is given on how it can be modified for the use of other probe liquids.

This study systematically characterises a matrix of water-based flexographic inks with respect to their rheology, surface tension and wetting of liquid packaging board, to provide a basis for interpretation and prediction of their printing performance. For all pigment and acrylate polymer vehicles and mixing proportions the inks were shown to be shear thinning and thixotropic, with plastic viscosity, yield stress and storage and loss moduli increasing strongly with content of solution polymer (at comparable solids contents). The solution polymer decreases the static surface tension of the inks, but generally leads to an increase in their equilibrium drop contact angle on the polyethylene- (PE-) coated board due to increase in the ink-board interfacial energy. The solution polymer also decreases the drop spreading rate, and a simple model is tested to express the spreading dynamics in terms of equilibrium contact angle and a rate parameter given by the effective ratio of surface tension to viscosity.

The objective of this paper was to understand the effects of plasma activation, and thus influence of the surface energy and chemistry changes on offset print quality. Pigment coated and surface sized papers were treated with corona and atmospheric plasma in pilot and laboratory scales. The surface energy and surface chemistry changes were evaluated by contact angle and X-ray photoelectron spectroscopy (XPS). Offset printing was performed in laboratory scale with an IGT unit with predampening and in a pilot scale sheet-fed offset printing press. In addition, the ink setting rate was measured using an ink on paper tack tester. Plasma activation increased the surface energy of the papers. Furthermore, the polarity of the paper surface increased due to formed polar oxygen containing molecular groups. Due to differences in treatment times laboratory scale plasma treatment formed mainly carboxyl and ester groups, whereas pilot scale treatment induced mainly alcohol, ethers, aldehydes and/or ketones on paper surfaces. Printing evaluation showed that plasma activation influences both ink and water absorption properties. According to print tack results plasma activation led to faster ink-setting. With hydrophobic surface-sized paper plasma activation influenced the ink transfer, print gloss and density by changing dampening water absorption properties. The difference in surface chemistry with laboratory scale plasma treated samples was also reflected in the print quality properties. SEM imaging showed that too intense plasma activation can cause topography changes in addition to of the surface chemistry changes.

The objective of this paper was to understand the effects of plasma activation, and thus influence of the surface energy and chemistry changes on offset print quality. Pigment coated and surface sized papers were treated with corona and atmospheric plasma in pilot and laboratory scales. The surface energy and surface chemistry changes were evaluated by contact angle and X-ray photoelectron spectroscopy (XPS). Offset printing was performed in laboratory scale with an IGT unit with predampening and in a pilot scale sheet-fed offset printing press. In addition, the ink setting rate was measured using an ink on paper tack tester. Plasma activation increased the surface energy of the papers. Furthermore, the polarity of the paper surface increased due to formed polar oxygen containing molecular groups. Due to differences in treatment times laboratory scale plasma treatment formed mainly carboxyl and ester groups, whereas pilot scale treatment induced mainly alcohol, ethers, aldehydes and/or ketones on paper surfaces. Printing evaluation showed that plasma activation influences both ink and water absorption properties. According to print tack results plasma activation led to faster ink-setting. With hydrophobic surface-sized paper plasma activation influenced the ink transfer, print gloss and density by changing dampening water absorption properties. The difference in surface chemistry with laboratory scale plasma treated samples was also reflected in the print quality properties. SEM imaging showed that too intense plasma

Polystyrene films of 100 nm thickness were modified using plasma immersion ion implantation (PIII) with argon ions of energy 20 keV and fluences in the range 2 × 10 ¹⁴-2 × 10 ¹⁶ ions cm ^-2. The structure and properties of the films were determined by ellipsometry and FTIR spectroscopy, as well as AFM, wetting angle measurements, profilometry and optical microscopy. The effects of oxidation, carbonization, etching and gel-formation were observed. The etching rate was found to decrease with PIII fluence. The rates of degradation with increasing fluence of the aromatic and aliphatic parts of the polystyrene macromolecule were found to be similar. Oxidation of the polystyrene film ceases at fluences greater than 10 ¹⁵ ions cm ^-2. The surface morphology of the film did not change with PIII fluence. Washing with toluene produced surface wrinkling for low fluences up to 10 ¹⁵ ions cm ^-2 while at high fluences the modified films were stable.

The biocompatibility of Si⁺ implanted medical polyurethane was studied. Si ion implantation was performed at energies of 40, 60, 80, and 100 keV with doses ranging from 2 × 10¹³ to 2 × 10¹⁶ cm⁻² at room temperature. The results show that the wettability, blood adsorption, anticoagulability and anticalcific bahaviours of the surface were changed significantly by ion bombardment. The results of SEM and XPS analyses indicate that some of the original chemical bonds in the surface region were broken and the degree of destruction was increased after implantation, which was probably the main reason for the surface modification. ESR shows that the number of radicals is not beyond the range 10¹² to 10¹⁴ cm⁻³, which is advantageous for the clinical utilization of polyurethane.

Polymer surfaces typically have low surface tension and high chemical inertness and so they usually have poor wet-ting and adhesion properties. The surface properties can be altered by modifying the molecular structure using plasma immersion ion implantation (PIII). In this work, Nylon-6 was treated using oxygen/nitrogen PIII. The observed improvement in the wettability is due to the oxygenated and nitrogen (amine) functional groups created on the polymer surface by the plasma treatment. X-ray photoelectron spectroscopy (XPS) results show that nitrogen and oxygen plasma implantation result in C–C bond breaking to form the imine and amine groups as well as alcohol and/or car-bonyl groups on the surface. The water contact angle results reveal that the surface wetting properties depend on the functional groups, which can be adjusted by the ratio of oxygen–nitrogen mixtures.

Different plasma treatments in a rf discharge of Ar, He, or N₂ are used to etch, cross-link, and activate polymers like PC, PP, EPDM, PE, PS, PET and PMMA. Due to the numerous ways a plasma interacts with the polymer surface, the gas type and the plasma conditions must be adjusted on the polymer type to minimize degradation and aging effects. Wetting and friction properties of polymers can be improved by a simple plasma treatment, demonstrated on PC and EPDM, respectively. However, the deposition of ultra-thin layers by plasma enables the adjustment of wetting properties, using siloxane-based or fluorocarbon films, and further reduction of the friction coefficient, applying siloxane or a-C:H coatings. Nevertheless, the adhesion of plasma-deposited coatings should be regarded, which can be enhanced by depositing a graded layer.

Polyester and polyamide fabrics were treated with plasma under atmospheric pressure for different durations, 3, 5 and 7 s. The wettability of polyester and polyamide fabrics, measured in terms of contact angle and longitudinal wicking, was improved after plasma treatment. The oxygen content of the fabrics was increased indicating that hydrophilic groups had been introduced into the fabric leading to the improved wettability. However, there was no obvious improvement in dryability because bulk properties of the fibres did not change. Moreover, with the help of plasma treatment, water repellency of the fabrics was greatly improved when water repellency finishing agent was added.