One of the main differences between low-pressure and atmospheric-pressure plasma treatments is that there is little moisture involved in the low-pressure plasma treatment, although moisture could exist at the wall of the vacuum chamber or react with the substrate after plasma treatment, while in the atmospheric-pressure plasma treatment moisture exists not only in the environment but also in any hygroscopic substrate. In order to investigate the influence of environmental moisture on the effect of atmospheric pressure plasma treatment, ultra-high-modulus polyethylene (UHMPE) fibers were treated using an atmospheric-pressure plasma jet (APPJ) with 10 l/min helium gas-flow rate, treatment nozzle temperature of 100°C and 5 W output power. The plasma treatments were carried out at three different relative humidity levels, namely 5, 59 and 100%. After the plasma treatments, the surface roughness increased while the water-contact angle decreased with increasing relative humidity. The number of oxygen containing groups increased as the environmental moisture content increased. The interfacial shear strength of the UHMPE fiber/epoxy system was significantly increased after the plasma treatments, but the moisture level in the APPJ environment did not have a significant influence on the adhesion properties. In addition, no significant difference in single fiber tensile strength was observed after the plasma treatments at all moisture levels. Therefore, it was concluded that the environmental moisture did not significantly influence the effect of atmospheric-pressure plasma treatment in improving interfacial bonding between the fiber and epoxy. The improvement of the interfacial shear strength for the plasma-treated samples at all moisture levels was mainly due to the increased surface roughness and increased surface oxygen and nitrogen contents due to the plasma etching and surface modification effect.

Polyethylene (PE) samples were activated by an atmospheric pressure plasma jet. The improvement in adhesive bond strength is attributed to the incorporation of oxygen-containing functional groups into the PE surface. Optical emission spectroscopy in combination with XPS analysis shows differences in the surface reactions for a plasma jet operated with air or pure nitrogen. The results indicate that the surface modifications take place in two different environments with respect to location and time: (a) reactions while the substrate is hit by the plasma jet, and (b) reactions outside the plasma jet after the treatment.

A study on oxygen-plasma treatment of ink-jet paper is presented. Paper was exposed to a weakly ionized, highly dissociated oxygen plasma with an electron temperature of 5 eV, a positive-ion density of 8 × 10¹⁵ m⁻³ and a density of neutral oxygen atoms of 5 × 10²¹ m⁻³. Optical emission spectroscopy (OES) was applied as a method for detection of the reaction products during the plasma treatment of the paper. OES spectra between 250 and 1000 nm were measured continuously during the plasma treatment. The wettability of the samples before and after the plasma treatment was determined by measuring the contact angle of a water drop. The appearance of the surface-functional groups was determined by using high-resolution x-ray photoelectron spectroscopy (XPS), while changes in the surface morphology were monitored with scanning electron microscopy (SEM). Already after 1 s of the plasma treatment the surface, which was originally hydrophobic, changed to hydrophilic, as indicated by a high absorption rate of a water drop into the paper. The OES showed a rapid increase of the CO and OH bands for the first few seconds of the plasma treatment, followed by a slow decrease during the next 40 s. The intensity of the O atom line showed reversed behaviour. The XPS analyses showed a gradual increase of oxygen-rich functional groups on the surface, while SEM analyses did not show significant modification of the morphology during the first 10 s of the plasma treatment. The results were explained by degradation of the alkyl ketene dimer sizing agent during the first few seconds of the oxygen-plasma treatment.

Recently, there has been increased interest in using atmospheric pressure plasmas for materials processing, since these plasmas do not require expensive vacuum systems. However, APGDs face instabilities. Therefore, special plasma sources have been developed to overcome this obstacle, which make use of DC, pulsed DC and AC ranging from mains frequency to RF. Recently, the APPJ was introduced, which features an α-mode of an RF discharge between two bare metallic electrodes. Basically, three different geometric configurations have been developed. A characterization of the APPJs and their applications is presented.

The surface free energy is an essential paper property affecting liquid/ink interaction with the ink-jet paper surface. Different ways of calculating surface energy components for ink-jet papers is introduced. The results given by the very useful van Oss–Chaudhury–Good (vOCG) bi-bidentate model are compared with simpler mono-bidentate and mono-monodentate models. The unbalance in the acid–base (AB) values of the vOCG-model is compensated for, and occasional negative roots obtained are removed when applying the simpler mono-bidentate- and mono-monodentate models. The simple and elegant mono-monodentate model produces comparable values with the other models, and is thus recommended. The calculated percent work of adhesion between the probe liquids and substrates correlates well with surface energy component values. Also the percent work of adhesion between the inks and substrates correlates with surface energy values.

The effect of ultraviolet (UV) radiation in the presence of ozone as a surface treatment for polycarbonate is examined in regards to changes in the wettability, adhesion, and surface mechanical properties. Standalone, 175-µm-thick films of a commercially available polycarbonate were exposed to UV radiation from sources of different power with various treatment times in the presence of supplemental ozone. Significant decreases in the water contact angle were observed after exposure to UV radiation in the presence of ozone. After several variations in the experimental setup, it was determined that the change in water contact angle is a function of the UV irradiance and the work of adhesion follows a master curve versus UV irradiance. Nanoindentation experiments revealed that the modulus of the top 500 nm of the surface is increased following UV exposure, attributable to surface cross-linking. Adhesion tests to the surface (conducted by a pneumatic adhesion tensile test instrument) showed little change as a function of UV exposure. Analysis of adhesion test failure surfaces with X-ray Photoelectron Spectroscopy (XPS) showed the locus of bond failure lay within the bulk polycarbonate and the measured bond strength is limited by the bulk properties of the polycarbonate and/or the creation of a weak boundary layer within the polymer.

This study describes experiments to quantify polymer surface energy changes after exposure to atmospheric plasma. Atmospheric plasma treatment permits surface functionalization at near-ambient temperatures. Polyethylene and polystyrene are treated with an atmospheric plasma unit. The increased surface energy and improved wetting characteristics lead to a significant adhesion improvement with adhesives that cannot be used without surface treatment.

Combined surface treatments using plasma fluorination and surface roughening were applied to investigate whether they could increase the peel property of PET beyond the value needed for use as a release coating of pressure-sensitive adhesive tapes. The peel strength of PET treated with CF₄/He APG plasmas decreased to approximately 100 N · m⁻¹, but not quite to the ideal value of PTFE, 20 N · m⁻¹. We also prepared PET with a rough surface (matte PET) to examine the effect of surface roughening. The matte PET peel strengths were decreased by plasma fluorination; the roughest matte PET showed even lower peel strength than PTFE. We conclude that the combined treatments could be effective in the formation of a surface with high peel property on PET.

Surface properties of a Melinex 800 PET polymer material modified by an atmospheric-pressure air dielectric barrier discharge (DBD) have been studied using X-ray photoelectron microscopy (XPS) and contact angle measurement. The results show that the material surface treated by the DBD was modified significantly in chemical composition, with the highly oxidised carbon species increasing as the surface processing proceeds. The surface hydrophilicity was dramatically improved after the treatment, with the surface contact angle reduced from 81.8° for the as-supplied sample to lower than 50° after treatment. Post-treatment recovery effect is found after the treated samples were stored in air for a long period of time, with the ultimate contact angles, as measured, being stabilised in the range 58–69° after the storage, varying with the DBD-treatment power density. A great amount of the C–O type bonding formed during the DBD treatment was found to be converted into the CO type during post-treatment storage. A possible mechanism for this bond conversion has been suggested.