## 4 Conclusions  
Cold plasma treatment is broadly used for modification of chemical composition and wettability of organic and nonorganic compounds [1; 2; 3; 4; 5; 6; 7; 8; 9; 51]. The influence of the plasma treatment on the surface chemical composition and properties of the polyvinylchloride catheters was explored with three different plasma sources. It can be concluded that the Corona, low pressure radiofrequency, and DBD plasma discharges increased essentially the hydrophilicity of PVC tubing. The Corona plasma treatment demonstrated the most pronounced influence on the eventual wettability of catheters. One-minute plasma treatment of the tubing by the Corona plasma discharge decreased the apparent contact angle from \(\theta~{}=~{}93\pm 0.5^{\circ}\) to \(\theta~{}=~{}30\pm 0.5^{\circ}\). The energy of water adhesion of pristine and plasma-treated PVC estimated with the Dupre formula is reported. Cold plasma treatment increased markedly the specific free surface energy of PVC, calculated with the Chibowski equation [45]. Kinetics of the hydrophobic recovery following the plasma treatment of PVC was explored [26; 27; 28; 29; 30]. The hydrophobic recovery following the plasma treatment of PVC is never complete, in other words the saturation contact angle \(\theta_{sat}\) is slightly lower than the initial apparent contact angle inherent for the pristine PVC. It is noteworthy that the kinetics of hydrophobic recovery following the plasma treatment is well-described by the exponential fitting suggested in [28] for all kinds of studied discharges. We established that the hydrophobic recovery following the cold plasma treatment was the slowest for the radiofrequency plasma discharge, and was most rapid for the DBD plasma treatment of PVC. The characteristic times inherent to the kinetics of the hydrophobic recovery of the plasma-treated PVC (\(\tau\cong 1.0\) day) supported the hypothesis that the effect was influenced by the bulk mobility of polymer chains [50]. Energy-dispersive X-ray spectroscopy of the chemical composition of the near-surface layers of the catheters indicated their oxidation, emerging from the cold air plasma treatment. This oxidation was irreversible and changed very slightly under one week ageing under ambient conditions. Thus, we conclude that the phenomenon of the hydrophobic recovery hardly correlated with the oxidation of the polymer (PVC) surface.  
Conceptualization, E.B. and S.N.-V.; methodology, I.L. and M.F.; validation, M.F. and Y.B.; formal analysis, I.L. and M.F.; investigation, I.L. and Y.B.; resources, Y.B.; data curation, I.L. and Y.B.; writing--original draft preparation, E.B.; writing--review and editing, E.B. and S.N.-V.; supervision, E.B. and S.N.-V.; project administration, S.N.-V.; funding acquisition, S.N.-V. All authors have read and agreed to the published version of the manuscript.  
This research was supported by the Ministry of Science & Technology, Israel (Grant No. 3-16288) supporting EB and SNV.  
Not applicable.  
The data presented in this study are available on request from the corresponding author.  
This work was supported by a grant from the Israel Ministry of Science and Technology, Grant no Merkava 3-16288 supporting EB and SNV. The authors are indebted to [PERSON] for her kind help with the energy-dispersive X-ray spectroscopy analysis of the samples. The authors are indebted to the anonymous reviewers for extremely fruitful suggestions.  
The authors declare no competing interest.