Abstract
<jats:p>The focus of this study is aimed at generating hollow cathode discharge (HCD) plasma inside three types of polymer tubes, resulting in the activation of tube's inner surfaces. To achieve this goal, both theoretical calculation and experiments were carried out to prove the adopted methodology was feasible. By applying optical emission spectroscopy, with line ratio and modified Boltzmann's plot methods, the plasma sheath could be estimated and applied to the prediction of HCD generation. To verify whether HCD prevails in the tube, the various power input (70 ~ 260 W), tube diameter (3 ~ 7 mm), and working pressure (0.1 and 0.4 torr) were selected. Accordingly, it was confirmed that the tube diameter must be greater than twice the plasma sheath, in order to form HCD, which would then activate the surface. Ar gas was used with a capacitive-coupled RF plasma system. PET, PU, and PTFE tubes were used in this study. The tubes’ inner surfaces were characterized with XPS, and water-contact-angle (WCA) analysis. The results also show that once HCD is generated inside the tubes, these tubes’ inner surface could become hydrophilic, and the values of WCA might decrease by 40°, 45° and 70° respectively for PET, PU, and PTFE, due to the combine effects of the enhanced ion bombardment and radical oxidation. XPS studies show that, for PET and PU, C-O and, particularly, C=O bonds increase significantly. For PTFE, the C-F bonds decrease, while carbonoxygen bonds increase. Overall, the surface activation is thought to be enhanced by ion bombardment attributable eventually to hollow cathode effect (HCE).</jats:p>