Using a multi-gas plasma jet, we generated plasmas of various gas species such as argon, oxygen, nitrogen, carbon dioxide, and air. Photometric measurements of colorforming reactions were used to identify singlet oxygen, OH radicals, hydrogen peroxide, NO radicals, nitrite, and nitrate, which are important sterilization agents that are generated in the liquid phase. Oxygen plasma generated the largest amount of singlet oxygen, OH radicals, and hydrogen peroxide. Air plasma generated NO radicals, nitrite, and nitrate. The pH of air plasma-treated water for 120 s dropped below 3.0. The air plasma sterilized Escherichia coli in distilled water after 120 s of treatment. In addition, when the initial pH was fixed below 3.6, E. coli was more effectively sterilized by oxygen plasma. Furthermore, dimethylsulfoxide, which is an OH radical scavenger, suppressed the sterilization effect of oxygen plasma.
An atmospheric pressure plasma source in which the gas temperature can be accurately controlled from below freezing point up to a high temperature has been developed. In general plasma devices, an electrical discharge is passed through a gas at about room temperature to generate plasma, so the plasma is at a temperature higher than room temperature; moreover, the gas temperature is determined by the discharge condition such as discharge power and plasma gas flow rate, so accurate temperature control is difficult. In the plasma source that has been developed in this research, the gas that is to be supplied to the discharge unit is first cooled using a gas cooler and then heated by a heater. The gas temperature of the produced plasma is measured, and feedback is sent to the heater. Thus, plasma at a desired temperature can be generated. Gas temperature control of the plasma over a range from −54°C to +160°C with a standard deviation of 1°C was realized. Spectroscopic characteristics of generated plasma were investigated. This plasma source/technique will realize that effective plasma is applicable for heat-sensitive materials such as paper, textile, polymer, and especially human tissue. Furthermore, it enables us to generate the plasma at optimal gas temperature for chemical reaction of each plasma treatment.Index Terms-Atmospheric plasma, biomedical electronics, plasma medicine, surface treatment.Hiroaki Kawano was born in Oita, Japan, in 1992. He received the B.E. degree in electrical and electronic engineering from the Oita National College of Technology, Oita, in 2014. He is currently pursuing the M.E. degree with the Tokyo Institute of Technology, Yokohama, Japan.
We performed an open-air-type plasma treatment of polytetrafluoroethylene (PTFE) at atmospheric pressure to increase the adhesion strength between PTFE and an Ag metal film obtained from Ag ink. When PTFE was Ar plasma-treated without H2O addition for 600 s, the coloration of the PTFE surface occurred, and the Ag/PTFE adhesion strength was 0.06 N mm−1. This adhesion strength was the same as that of the as-received PTFE (0.04 N mm−1). When the PTFE was Ar plasma-treated with the H2O addition of ca. 0.1% for 600 s, coloration did not occur, and the Ag/PTFE adhesion strength increased to 1.03 N mm−1. The effects of H2O addition to the Ar plasma on the Ag/PTFE adhesion strength, surface chemical composition, surface morphology, and the surface hardness were investigated and discussed in this study.
We performed open-air plasma treatment of polytetrafluoroethylene (PTFE) at atmospheric pressure to increase the adhesion strength between PTFE and an Ag metal film formed from Ag ink. Coloration of the PTFE surface occurred during 600 s treatment with Ar plasma. The Ag/PTFE adhesion strength was 0.06 N/mm. To resolve the problem of coloration and to improve the adhesion strength, O2 or H2 gas was added. During treatment with Ar + O2 plasma with O2 content of 0.33% for 600 s, no coloration occurred but the adhesion strength decreased to zero. During treatment with Ar + H2 plasma for 600 s, coloration did not occur. Moreover, the adhesion strength increased to 0.25-0.55 N/mm. These results showed that H2 addition was effective for preventing coloration and improving adhesion strength during long-period plasma treatment. Furthermore, the uniformity of surface treatment with Ar + H2 plasma was higher than that for Ar plasma.
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