This book describes the fundamentals and applicability of the atmospheric-pressure non-thermal plasma surface modification of materials. Non-thermal plasma modification is an effective procedure for chemical activation. In this book, the principles of non-thermal plasma surface modification and its application to various machine parts are described. By reading this book, technologists from a variety of fields can learn about plasma generation and surface treatment technology, which will assist them in performing advanced procedures. This book also explains the basics of atmospheric-pressure plasma and the principle of plasma treatment in an easy-to -understand manner and also provides examples of the application of atmospheric-pressure plasma surface modification technologies to plastics, glass, polymers, and metals. After reading this book, readers can get the knowledge that researchers need to apply the methodology to meet their own research goals. T he book is self-contained in the sense that it spans the divide between the fundamentals and more advanced content regarding applications. Many engineers and graduate students working in this field get many helps.

Poly(butylene succinate) (PBS) films were processed by a radio frequency (RF; 13.56 MHz) low-pressure plasma of oxygen and argon/oxygen, and an oxygen plasma with an argon post-crosslinking plasma to improve their wettability property. Specimens were treated at different times with fixed power processing of 100 W (0.3 W/cm2) and a fixed pressure of 10 Pa. A significant change in hydrophilicity evaluated by the water contact angle was observed. The contact angle of a water drop decreased from 80° for the untreated sample to values lower than 5° for plasma-treated samples. The effect of ageing on the wettability of PBS substrates was also examined, showing a more pronounced trend in the first 4 h and reaching a plateau in the following days. However, partial surface hydrophilicity was maintained for up to 15 days. A practical application of the surface functionalization produced by plasma was obtained via the deposition of SiOx onto PBS surfaces; the study of films’ oxygen permeability demonstrated that the plasma pre-treatment increased the adhesion between PBS and SiOx, resulting in significantly improved oxygen barrier properties. In order to evaluate the morphology and roughness modification caused by plasma exposure, atomic force microscopy characterization was carried out. Chemical information about treated surfaces, such as an increase in oxygen functional groups during plasma exposure, was measured by Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy. Finally, the effects of plasma on crystallinity were investigated by X-ray diffraction.

Polyolefins are well-known and the most commonly used polymers worldwide. Advantages like outstanding mechanical properties, chemical resistance, low cost, and processability are neighboring with some drawbacks like relatively high gas and vapor permeability, low surface energy. This chapter introduces surface plasma modification as an environmentally friendly, fast, and versatile technique. Details regarding different plasma reactor designs, generation methods, working parameters suitable for treating polyolefins are presented. Furthermore, plasma activation, grafting, and etching are described as the most commonly used techniques for surface energy modification to enhance polyolefins' biocompatibility, printability, adhesion to materials, and other parameters. For instance, plasma activation cross-linking of the polymer chains can be achieved, which leads to gas and vapor permeability improvement. Choice of working conditions allows controlling the degree of cross-linking, the type, and the concentration of the incorporated functional groups on the surface. Plasma polymerization is introduced as a technique for coating deposition with different properties and functionality depending on the operating parameters and monomer selection. Improvement of barrier layer performance and modification of the surface energy are the main applications of plasma polymerization of polyolefins.

The hydrophobic characteristic of polymers is considered a limiting property for its applications. To some extent, this has been overcome by techniques such as non-thermal plasma, which, even with a few seconds of application, can increase the surface energy and hydrophilic character of polymers. However, this technique is associated with advantages and disadvantages. Surface degradation related to oxidation and crosslinking are considered irreversible changes, in most cases, while the hydrophobic character is quickly restored, presenting a challenge to researchers all over the world. As a reversible behavior, efforts have been made to understand this particular characteristic of the hydrophobic recovery (or the aging effect) of polymers. The application of non-thermal plasma on polymeric surfaces has also been used in biomedicine as a sterilization device to control the growth of biofilms, as well as to increase the biocompatibility of prosthetic surfaces. This chapter discusses some particular characteristics of polyolefins exposed to plasma.

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.

Polyimide films are currently of great interest for the development of flexible electronics and sensors. In order to ensure a proper integration with other materials and PI itself, some sort of surface modification is required. In this work, microwave oxygen plasma, reactive ion etching oxygen plasma, combination of KOH and HCl solutions, and polyethylenimine solution were used as surface treatments of PI films. Treatments were compared to find the best method to promote the adhesion between two polyimide films. The first selection of the treatment conditions for each method was based on changes in the contact angle with deionized water. Afterward, further qualitative (scratch test) and a quantitative adhesion assessment (peel test) were performed. Both scratch test and peel strength indicated that oxygen plasma treatment using reactive ion etching equipment is the most promising approach for promoting the adhesion between polyimide films.

In the study reported in this paper, a series of reproducible conditions were employed to uniformly functionalize nylon 6 surfaces using a commercially available, low-frequency (40 kHz), low-pressure plasma system, utilizing oxygen plasma as a reactive gas. Initially, the plasma-treated samples were investigated using static contact angle measurements, showing a progressive increase in wettability with increasing plasma activation time between 10 and 40 s. Such an increase in wettability (and therefore increase in adhesive capabilities of the surfaces) was attributed to the creation of surface C-OH, C=O, and COOH groups. These surface-chemical modifications were characterized using x-ray photoelectron spectroscopy (XPS) and static secondary ion mass spectrometry (SSIMS). Surface radical densities were also shown to increase following plasma activation, having been quantified using a radical scavenging method based on the molecule 2,2-diphenyl-1-picrylhydrazyl (DPPH). The samples were imaged and analyzed using scanning electron microscopy (SEM) and atomic force microscopy (AFM), to confirm that there had been no detectable alteration to the surface roughness or morphology. Additionally, the “hydrophobic recovery” or “ageing” of the activated polymer samples, post-plasma treatment, was also investigated in terms of wettability and surface-chemistry, with the wettability of the sample surfaces decreasing over time due to a reduction in surface-oxygen concentration.

The interaction between inks and substrates is critical during printing. Adhesion of the ink film is determined by the reciprocal interactions of polar and nonpolar (dispersive) components between polymer films and inks. The greater the similarity between the polar and dispersive components of inks, coating and substrates, the better the wetting and adhesion on the surface of printing substrate. Various liquid materials in printing such as inks, varnishes, lacquers, and adhesives contain high ratios of water. The highly polar nature of water makes the interaction of these materials unsuitable with predominantly disperse polymer surfaces. Some films with polyolefin structure, especially polypropylene, and polyethylene, are nonpolar and cannot form strong bonds with ink, varnish, or lacquer coatings due to their chemical structure. Increasing surface energy components overcomes the poor wetting and adhesion on polymer surfaces. In this review, the topics of water contact angle measurement and determination of surface energy, surface tension, and using sessile drop method for the wettability and ink adhesion of polymer films are surveyed. Information on structural and chemical processes was given that assists in obtaining wettable film surfaces. Recommendations were made for good adhesion and printability based on surface treatment methods and ink modification.

Plasma treatment is one of the methods currently used to obtain polymeric materials with surface properties appropriate to the functionality for which they were designed. However, the effects achieved after surface modification are not always long lasting and involve chemical and physical changes in the outermost layer. In this context, the effects of both argon and oxygen plasma on polylactic acid (PLA) films deposited on titanium were studied to determine which physical and chemical processes occur at the surface, and their duration. Regarding physical surface changes, there were scarcely any differences between both plasmas: roughness was very similar after treatments, root mean square height (Sq) being 10 times higher than the control, without plasma. Water contact angle (WCA) showed that the surface became more hydrophilic after application of the plasma, although hydrophilization was longer lasting in the case of argon treatment.

With regard to chemical changes, it was observed that the argon plasma treatment caused greater fragmentation of the polymer chains, and increased crosslinking between them. ToF-SIMS analysis made it possible to propose mechanisms to explain the formation of the fragments observed.