Surface properties of modern materials are usually inadequate in terms of wettability, adhesion properties, biocompatibility etc., so they should be modified prior to application or any further processing such as coating with functional materials. Both the morphological properties and chemical structure/composition should be modified in order to obtain a desired surface finish. Various treatment procedures have been employed, and many are based on the application of non-equilibrium gaseous media, especially gaseous plasma. Although such treatments have been studied extensively in past decades and actually commercialized, the exact mechanisms of interaction between reactive gaseous species and solid materials is still inadequately understood. This special issue provides recent trends in nanostructuring and functionalization of solid materials with the goal of improving their functional properties.

We are presenting recent advances in surface functionalization of materials such as functional polymers using gaseous plasma treatments. Functionalization is a result of chemical interaction between solid materials and reactive plasma species including charged particles, neutral radicals, excited species and UV radiation. The degree of surface functionalization depends on the type of polymers and fluxes of reactive plasma species. An appropriate choice of plasma parameters thus enables almost arbitrary tailoring of the surface wettability. This review paper gives a brief introduction to the formation of reactive gaseous species upon plasma conditions in different discharge configurations and describes plasma-surface interaction with an emphasis on the differences between different reactive plasma species. Analysis of the relevant literature is given and correlations between treatment parameters and surface finish are drawn. Numerous authors have used plasma treatment for modification of the surface functionalities, however, the obtained surface properties often differ even for the same materials. The reason for such diverse results is the application of various gaseous discharges for plasma generation. Apart from the type and amount of functional groups induced by plasma treatment, the surface functionality depends also on the surface morphology on the sub-micron scale; therefore, this effect is stressed as well. Finally, some future guidelines are given.

Polymer materials are widely employed in many fields due to the ease with which they can be formed into complex shapes, their versatile mechanical properties, light weight, and low cost. However, many applications are hindered by the chemical compatibility of polymer surfaces, which are generally hydrophobic and bond poorly to other media such as paints, glues, metals and biological media. While polymer surfaces can be treated by wet chemical processes, the aggressive reagents employed are detrimental to the environment, limiting the range of modifications that can be achieved by this route. Plasma functionalization is an attractive alternative, offering great versatility in the processed surface characteristics, and generally using environmentally benign compounds such as rare gases, oxygen and nitrogen, as well as very small quantities of organic precursors. Since the modified surfaces are only a few monolayers thick, these processes are extremely rapid and low in cost. The first industrial process to be developed was plasma oxidation, which increases the surface energy of the polymer, improving the adhesion of paint, glue and metal to the component. Plasma oxidation can be achieved using both low-pressure and atmospheric pressure (APP) discharges. Subsequently, many other processes have emerged, allowing other functional groups to be grafted, including amines, hydroxyl and carboxylic acid groups. Plasma polymerization, starting from gaseous monomers, allows a whole new family of surface chemistries to be created. These processes have many exciting applications in the biomedical field due to the control they give on biocompatibility and selective interaction with living cells. This article will present the fundamentals of plasma interactions with polymers, the plasma devices employed (both at low-pressure and at APP) with their advantages and drawbacks, and a survey of current and future applications.

In this study, recent advances in tailoring the surface properties of polymers for the optimization of the adhesion of various coatings by non-equilibrium gaseous plasma are reviewed, and important findings are stressed. Different authors have used various experimental setups and reported results that scatter significantly and are sometimes contradictory. The correlations between the processing parameters and the adhesion are drawn, and discrepancies are explained. Many authors have explained improved adhesion with the adjustment of the surface free energy or wettability of the polymer substrate and the surface tension of liquids used for the deposition of thin films. The adhesion force between the polymer substrate and the coating does not always follow the evolution of the surface wettability, which is explained by several effects, including the aging effects due to the hydrophobic recovery and the formation of an interlayer rich in loosely bonded low molecular weight fragments.

Nonthermal plasma (NTP), or cold plasma, has shown many advantages in the agriculture sector as it enables removal of pesticides and contaminants from the seed surface, increases shelf life of crops, improves germination and resistance to abiotic stress. Recent studies show that plasma treatment indeed offers unique and environmentally friendly processing of different seeds, such as wheat, beans, corn, soybeans, barley, peanuts, rice and Arabidopsis thaliana, which could reduce the use of agricultural chemicals and has a high potential in ecological farming. This review covers the main concepts and underlying principles of plasma treatment techniques and their interaction with seeds. Different plasma generation methods and setups are presented and the influence of plasma treatment on DNA damage, gene expression, enzymatic activity, morphological and chemical changes, germination and resistance to stress, is explained. Important plasma treatment parameters and interactions of plasma species with the seed surface are presented and critically discussed in correlation with recent advances in this field. Although plasma agriculture is a relatively new field of research, and the complex mechanisms of interactions are not fully understood, it holds great promise for the future. This overview aims to present the advantages and limitations of different nonthermal plasma setups and discuss their possible future applications.

Surface modification of polymers has become a vibrant field of research on account of a myriad of rationales which stimulated numerous efforts. The current paper serves as a condensed survey of the advances made through different approaches adopted for tuning the surface properties of polyvinyl chloride as a homopolymer extensively used on a large scale. Though it does not address all challenges involved, this paper communicates and highlights, through concise discussion, the findings of the efforts undertaken in recent decades. It is ultimately concluded with a perspective of the huge capacities and promising future directions.