## 1 Introduction  
A diversity of engineering applications calls for the modification of the surface properties of industrial polymer materials, including their adhesion and wettability. These applications include packaging, protective coatings, adhesives, textile, printing, etc. In the fields of medicine and biotechnology, many products such as catheters and medical implants are completely or partly made of polymers. In contact with biological systems, compatibility of these materials is not always specified. Medical applications often demand the modification of the properties of polymer surfaces. Plasma techniques supply an appropriate tool for the generation of demanded surface properties [1; 2; 3; 4; 5; 6]. Plasma modified materials fulfil the requirements for bioactivity in medicine; for example, the inclusion of antimicrobial agents (metal nano-particles, antimicrobial peptides, enzymes, etc.) in plasma- modified materials (polymeric, metallic, etc.) alters them to produce superior antibacterial biomedical devices with a longer active life [4].  
Various kinds of discharges were already applied for the surface modification of medical polymers including the atmospheric [7] and low pressure plasma discharges [8]. The plasma treatment creates a complex mixture of surface groups, constituting surface physical and chemical properties, which results in an essential increase in the specific surface free energy and consequent change in the wetting properties of the plasma modified surface [9; 10; 11; 12]. It was demonstrated recently that the plasma treatment may result in the cross-linking of polymer molecules [13]. It was reported that plasma treatment leads to the essential electrical charging of a polymer surface observed for both synthetic and biological polymers [14, 15]. It is agreed that the cold plasma modification increases the specific surface energy of polymers, thus resulting in their pronounced hydrophilization [16, 17, 18, 19, 20, 21]. At the same time the precise physico-chemical mechanism of this hydrophilization remains debatable. It was suggested that the hydrophilization of organic surfaces by plasmas may be at least partially related to the re-orientation of hydrophilic moieties constituting organic molecules [22, 23]. The oxidation of plasma-treated surfaces and removal of low-mass fragments present on organic surfaces also contribute to hydrophilization [24, 25].  
It was reported that the specific surface energy of cold plasma-treated polymers decreases with time and consequently hydrophilization provided by plasma treatment is partially lost with time [26, 27, 28, 29, 30]. This process is called hydrophobic recovery [26, 27, 28, 29, 30]. It was demonstrated experimentally that hydrophobic recovery is stipulated by the re-orientation of the polar groups constituting the polymer chains, which were oriented by the plasma treatment [28]. A model for the hydrophobic recovery due to a combination of two thermodynamically non-equilibrium processes, diffusion and molecular reorientation, was suggested [30]. Our manuscript focuses on the estimation of influence of cold plasma treatment on the wettability and hydrophobic recovery of medical grade Polyvinylchloride (PVC), broadly used for manufacturing of medical catheters. Cold plasma treatment of PVC was reported by several groups [31, 32, 33, 34], however the experimental data related to this polymer remain sparse. We report a comparative study of the impact of various plasma discharges, including the Corona discharge, dielectric barrier (DBD) discharge, and radiofrequency low pressure air plasma discharge on the wettability and hydrophobic recovery of medical grade PVC.