## 3 Results and Discussion
### Study of the Hydrophobic Recovery Following the Plasma Treatment of the Medical Grade PVC  
The change in the surface properties of polymers induced by the cold plasma treatment is lost with time [26; 27; 28; 29; 30]. This effect is called the \"hydrophobic recovery\" [26; 27; 28; 29; 30]. An understanding of the kinetics and mechanisms of the hydrophobic recovery is crucial for applications of plasma-treated polymers. The pronounced hydrophobic followed the plasma treatment of plasma-treated PVC tubing as illustrated with Figures 5-7, representing \begin{table}
\begin{tabular}{c c} \hline \hline
**PVC Tubing** & **Specific Energy of Adhesion, \(W_{\text{,}}\frac{\text{mJ}}{\text{m}^{2}}\)** \\ \hline Pristine & \(70\pm 1\) \\ Corona discharge treated & \(132.5\pm 2\) \\ Radiofrequency plasma discharge treated & \(111.5\pm 5\) \\ DBD plasma discharge treated & \(101.5\pm 5\) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Specific energy of adhesion established with the Dupre formula for the pristine and plasma-treated PVC tubing. Figure 4: Impact of the dependence of the equilibrium apparent contact angle at the time of plasma treatment is presented. (**A**) Treatment with the Corona plasma discharge. (**B**) Treatment with the radiofrequency plasma device. (**C**) Treatment with the dielectric barrier (DBD) plasma unit. the time evolution of the apparent contact angle measured on the plasma-treated medical grade PVC for various kinds of plasma discharges. Figure 5: Kinetics of the hydrophobic recovery of PVC following Corona plasma treatment is shown. Blue circles correspond to the 15 s treatment; red circles correspond to the 30 s treatment; black circles correspond to the 45 s treatment; and green circles correspond to the 60 s treatment. The dashed line corresponds to the exponential fitting with Equation (5). The parameters of fitting are supplied in Table 2.  
Figure 6: Kinetics of the hydrophobic recovery of PVC following the radiofrequency plasma treatment is depicted. Blue circles correspond to the 15 s treatment; red circles correspond to the 30 s treatment; black circles correspond to the 45 s treatment; and green circles correspond to the 60 s treatment. The dashed line corresponds to the exponential fitting with Equation (5). The parameters of fitting are supplied in Table 3. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Exposure Time, s** & \(\theta_{\text{Sat}}\) & \(\tilde{\theta}\) & **T, Days** \\ \hline
15 & 86 \(\pm\) 1.2 & 27 \(\pm\) 2.7 & 0.7 \(\pm\) 0.2 \\
30 & 88 \(\pm\) 0.2 & 13 \(\pm\) 0.3 & 1.3 \(\pm\) 0.1 \\
45 & 83 \(\pm\) 2.2 & 31 \(\pm\) 5.6 & 0.5 \(\pm\) 0.3 \\
60 & 85 \(\pm\) 2.5 & 17 \(\pm\) 3.4 & 1.5 \(\pm\) 0.1 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Parameters of the exponential fitting of the kinetics of hydrophobic recovery following the DBD treatment of PVC. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Exposure Time, s** & \(\theta_{\text{Sat}}\)\({}^{\circ}\) & \(\tilde{\theta}\)\({}_{\sigma}\)\({}^{\circ}\) & **\(\tau\), Days** \\ \hline
15 & 73 \(\pm\) 2.8 & 45 \(\pm\) 3.7 & 2.2 \(\pm\) 0.5 \\
30 & 60 \(\pm\) 1.6 & 25 \(\pm\) 2.1 & 2.2 \(\pm\) 0.5 \\
45 & 60 \(\pm\) 1.2 & 27 \(\pm\) 2.6 & 1.2 \(\pm\) 0.3 \\
60 & 62 \(\pm\) 5.3 & 34 \(\pm\) 5.7 & 2.7 \(\pm\) 1.3 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Parameters of the exponential fitting of the kinetics of hydrophobic recovery following the Corona plasma treatment of PVC. Figure 7: Kinetics of the hydrophobic recovery of PVC following the DBD plasma treatment is depicted. Blue circles correspond to the 15 s treatment; red circles correspond to the 30 s treatment; black circles correspond to 45 s treatment; and green circles correspond to the 60 s treatment. The dashed line corresponds to the exponential fitting with Equation (5).