The effect of oxygen plasma treatment on adhesion and surface properties of polypropylene (PP) was assessed. An oxygen rich modified PP layer, immiscible with bulk PP, was formed by the treatment. Contact angle measurements showed that macromolecular motions led with time to rearrangements of the surface layer drastically decreasing its wettability, while its composition, measured by XPS, remained unaffected.The shear strength of PP-epoxy joints increased after plasma treatment. The locus of failure was found to occur at the PP/epoxy interface for untreated PP, within PP in the case of oxygen-plasma-treated samples, close to the modified PP/bulk PP interface. This result suggests that the plasma treament improves the interaction at the PP/epoxy interface, but weakens the mechanical strength of the surface layer thereby creating a weak point at the modified PP/bulk PP interface.

Protective properties of zinc coating increase with an additional coating such as: chromate, phosphate, paint and polymer coating. Besides, additional treatment of zinc coating serves decorative purposes as well. The paper presents the influence of additional coating of zinc coating on their adhesive properties which are especially helpful in processes where adhesion plays an essential role. These processes include among others: gluing, painting or varnishing. Adhesive properties are characterized by the value of surface free energy.

The surface of the bio-material polymethyl methacrylate (PMMA) was treated with CO₂, Nd:YAG, excimer and high power diode laser (HPDL) radiation. The laser radiation was found to effect varying degrees of change to the wettability characteristics of the material depending upon the laser used. It was observed that interaction with CO₂, Nd:YAG and HPDL effected very little change to wettability characteristics of the PMMA. In contrast, interaction of the PMMA with excimer laser radiation resulted an increase in a marked improvement in the wettability characteristics. After excimer laser treatment the surface O₂ content was found to have increased and the material was seen to be more polar in nature. The work has shown that the wettability characteristics of the PMMA could be controlled and/or modified with laser surface treatment. However, a wavelength dependence of the change of the wetting properties could not be deduced from the findings of this work.

The paper describes an experimental investigation of the possibility of industrial modification of surface wettability and adhesion of polymers by the action of a plasma of a gliding discharge generated in air at atmospheric pressure in a simulated production process. The test material was polypropylene plates (PP). The modification was performed by a device with a multi-electrode (four pairs) system, which is not common. The quality of pre-processing and usability was evaluated primarily in terms of the industrial requirements, which means a change in wettability and adhesion expressed by the contact angle/surface free energy value in dependence to sample exposure time expressed by the conveyor belt speed. The surface free energy assessment of a treated polymeric surface by contact angle measurement was carried out by analyzing static sessile drops and evaluated by Owens–Wendt–Rabel–Kaelble (OWRK) model. The results determined a set of operating parameters at which the modification process meets the industrial requirements. By evaluating the change in surface free energy in relation to the storage time, the degree of hydrophobic recovery of the treated samples, i.e. the time stability of the plasma-treated surface, was also determined. It has been found that plasma-treated PP surface fully meets industrial demands and can be stored for at least 50 days.

A novel absorption test method was developed based on a modification of the Bristow Absorption Apparatus. The proposed method combines corona treatment (CT) with short contact time absorption behavior to study particularly ink wetting and sorption on substrates in-line. The method makes it possible to study e.g. the coagulation of pigment inks induced by deposited charges i.e. electrocoagulation, the effect of short contact times on liquid/substrate interactions, and problems related to charge decay such as whiskering. In-line measurement with a short delay time minimizes the effect of ambient conditions (heat, moisture) on charge decay, and thus simulates the conditions in commercial digital printing processes.The functionality of the method was evaluated by testing paper samples with and without polymer coatings. Uncoated samples were used to study absorption properties. It was found that in some cases the CT changes both the wetting and absorption of ink and that in other cases the main changes are in the absorption behavior. Four CT levels (0, −100, −450, and −900 W*min/m2) were studied and it was found that the highest treatment level increased the absorption of the applied inkjet ink the most. As expected, the contact time between liquid and substrate was found to be an important variable affecting the absorption. Print density and mottle were determined on coated samples with the CT levels of 0, −160, and +160 W*min/m2. CT improved print density significantly, whether the treatment was positive or negative, and also reduced the mottling tendency.

The wetting (or dewetting) of a solid by a liquid is an integral part of many important processes such as coating, petroleum recovery, distillation and the handling of liquid fuels in low gravity conditions. Several experiments^1–4 have shown that wetting lines (where liquid, air and solid phases meet) which are straight at slow rates of movement over the solid have a sawtooth shape at sufficiently high speeds. We now offer a quantitative explanation for this phenomenon based on the postulate that, for a given system, there is a maximum rate at which wetting can proceed. The consequences of this interpretation are likely to be important, since, in many practical situations, the aim is to maximise the speed of wetting without entraining the displaced phase.

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

THE nature of active nitrogen, the mechanism of its afterglow¹, and its gas phase reactions with organic molecules² have been discussed. I have now investigated a heterogeneous active nitrogen reaction at a polymer surface.

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.

A plot of the initial spreading pressures F sub ba or initial spreading coefficients S sub ba against the surface tensions of a homologous series of organic liquids b can be used to determine the critical surface tension for spreading on a second substrate liquid phase a. Straight-line relations are found for various homologous series. The intercept of that line with the axis of abscissas F sub ba 0, or S sub ba 0 defines a value of spreading for that series. This method is advantageous because it eliminates the need for measuring or calculating the contact angle of lens b floating on liquid a, it can be applied to any liquid substrate, and it is applicable even when spreading does not lie within the range of surface tensions of the members of the homologous series of liquids b. The value of spreading for the waterair interface was determined in this way using several homologous series of pure hydrocarbon liquids. The lowest value found was 21.7 dynescm at 20 deg C for the n-alkane series. Higher spreading values were obtained using olefins or aromatic hydrocarbons as the result of interaction between the unsaturated bond and the water surface. Since the results are analogous to those reported earlier for solid surfaces, it is concluded that the clean surface of water behaves as a low-energy surface with respect to low-polarity liquids. This result is to be expected if only dispersion forces are operative between each alkane liquid and water.