The Regulation Mechanism Of Water On Plasma Jet And Its Diagnosis And Application

The hydroxyl radical?·OH?is mainly produced by plasma reacting with water vapor.It is the strongest oxidation in plasma,which is widely used in biological medicine and sterilization.What is more,the water vapor includes two parts:one part is the water vapor in the working gas,the other part is the ambient water content.However,a large number of water molecules absorb energetic electrons,resulting the plasma jet shorter and affecting the plasma propagation.Considering the above two aspects,in this paper,an air-water micro-hollow cathode plasma jet assisted by the preionization technique is designed and fabricated,which is used to study the effect of water vapor on working gas.In addition,the Ar cold plasma jet affected by the ambient water content is investigated.First,an atmospheric micro-hollow cathode plasma jet assisted by the preionization of ring-needle discharge is generated.The influence of voltage,gas flow,water content and power on the length of plume,temperature and the intensity of·OH,O and NO is studied.Meanwhile,the production of O₃ is measured by the absorption spectrum.The results shows that the jet length is longer obviously with preionization,at the same time the temperature increases.When the total power is the same,with the decrease of mico-hollow discharge power,the jet length decrease little and the temperature increase small.Besides,the intensity of NO and·OH can be detected only in DC mode,and O in both modes.With the action of preionization,the intensity of NO is diminished,whereas the intensity of O and·OH are enhanced.What is more,with the water content increasing,the intensity of·OH is promoted,but the intensity of O decreases first and then increases.The changing rule of NO is opposite to the intensity of O.The steady state production of O₃ can nearly be detected at low voltage as well as without preionization.Nevertheless,in order to increase the products of·OH in the Argon plasma jet,the ambient humidity is regulated instead of working gas to avoid the instability of discharge in this paper.We apply absorption and emission spectroscopy,static water contact angle test,X-ray photoelectron spectroscopy?XPS?and scanning electron microscopy?SEM?to study the relationship of hydrophilicity,ambient humidity and·OH density.The results show that at water content of 6 mg/L,the electron excitation temperature and the excited state Ar reach the peak value.Thus,the·OH density reaches maximum of 4×10¹⁵ cm^-3.Under this condition,more O-polar groups are injected into the surface because of the high production of·OH.At the same time,the etching effect of the plasma is the strongest.Thus,the smallest contact angle is reduced to 37°.While·OH product at water content of2.3 mg/L is higher than that of 9.5mg/L,the contact angle of the former is larger because of the etching effect.In a word,the proposed method is a convenient way to increase the efficiency of plasma surface modification.