The reactive chemical species generated in an atmospheric-pressure plasma jet (APPJ), such as hydroxyl radical and atomic oxygen, are generally regarded as the major sources for several biomedical applications. In this paper, we propose an APPJ with a 25-kHz high-voltage powered stainless steel tube fixed inside a quartz tube and an aluminum grounded electrode that is wrapped around the quartz tube. The results show that the radical intensities of atomic oxygen and hydroxyl radical, gas temperature, and power absorption increase with increasing distance of discharge gap distance under the same applied voltage. Increasing the width of grounded electrode increases gas temperature and causes higher power absorption but only slight change of radical generation. We have applied the APPJ with the conditions of highest radical generation (grounded electrode width = discharge gap distance = 15 mm) for effectively sterilizing Streptococcus mutans within 15 s, which shows a highly potential application for root canal disinfection.

No abstract

In this paper, a plasma-induced hemi-wicking phenomenon observed on hydrophobic sanded polymer surfaces, polypropylene (PP), polyethylene terephthalate (PET) and polyethylene (PE) is reported. An atmospheric-pressure argon plasma jet was used to treat a limited area of the carefully sanded polymer surfaces to induce the hemi-wicking phenomenon. Such hemi-wicking triggered by the plasma activation is different from the traditional type, which is achieved purely by the surface topography. Surface analyses by X-ray photoelectron spectroscopy (XPS) and water contact analysis (WCA) show that the combination of sanding and plasma treatment increased the oxygen-to-carbon ratio, which is highly beneficial for surface hydrophilicity. The shear stress tests show that the combination of sanding and plasma treatment can enhance the shear stress by 125%, 95%, and 296% on PP, PET, and PE, respectively. The study shows that the newly developed technique by combining the sanding and plasma processing for polymers could be a potentially useful method in future industry applications.