Research On Asymmetric DBD Discharge Space Structure Identification And Polypropylene Modification

Dielectric Barrier Discharge(DBD)can produce stable low temperature plasma at normal temperature and pressure,and has been widely used in many fields such as ozone generation,material surface modification,gas flow control and so on.DBD's common discharge mode is filamentous discharge at atmospheric pressure.but In the material surface modification and other industry fields often request discharge space has higher uniformity.So it's the hot pints and difficulty for the scholar to improve and estimate the uniformity of the discharge space in the practical industrial applications.About how to improve the homogeneous degree of the discharge space,the researchers are from the following several aspects.(1)using nert gas as a gas medium;(2)discharge generated under the environment of low pressure;(3)utilizing asymmetric DBD as plasma source.Unlike the uniform discharge of any filamentous discharge channel that does not exist in the strict range of ns magnitude.In actual industrial production,it is not necessarily limited to the uniform discharge on this theoretical definition.In contrast to that,the approximate uniform discharge formed by many filamentous channel is more practical.So it also raises to the problems about discharge space structure identification and evaluation of uniform degree.About the identification of DBD discharge space,Commonly used method are measurement of electric parameters,ICCD high-speed camera and digital image processing technology.Based on the asymmetric DBD as the research object.This paper studied the discharge space structure of needle—to—plane and mesh—to—plane DBD respectively by ICCD high-speed camera and digital image processing technology,And select the mesh—to—plane DBD to modified the surface of polypropylene(PP)samples.the research results are as follows:The needle-to-plate DBD(gas gap 12mm)exhibits different discharge modes under the conditions of atmospheric pressure.When Ar was used as gas dielectric,micro-discharge filament mode and glow-like discharge mode occurred in the positive and negative period of the discharge voltage(4k V).When N2 was used as gas dielectric,corona discharge mode was observed,There was a bright spot near the needle electrode(12kV).As the discharge voltage increased to 15 kV,micro-discharge filament mode and glow-like discharge mode occurred in the positive and negative period of the discharge voltage respectively.When air was used as gas dielectric and discharge voltage was 12 kV,corona discharge mode similar to that under N2 condition was obtained,while micro-discharge filament mode occurred during the whole discharge period as the discharge voltage further increased to 15 kV.Grayscale histogram(GLH)and Fourier energy spectrum(FES),which are commonly used in image processing technology,are used to identify the discharge space structure of mesh—to—plane DBD.And the uniformity of the discharge space is quantitatively evaluated by using the CV value representing the degree of dispersion of the image gray scale u(x,y).mesh—to—plane DBD's spatial structure will turn from discharge with characteristic of spatial period to filamentary discharge under the condition of nitrogen or air.The GLH of periodic discharge is similar to single gaussian distribution,and the Fourier energy spectrum appear as regular structure.With discharge voltage increasing,discharge channel will merge together.The spatial structure will be filamentary discharge.GLH is mixtures of Gaussians distribution.and the Fourier energy spectrum appear as oval.When the gas medium is argon.The spatial structure will be filamentary discharge as long as the discharge occurs.This chapter also optimized the mesh size(L)of mesh electrode.If L is small enough,The CV value of the discharge image is smaller than that of the plane—to—plane DBD structure with the same electrode area.That is,the uniformity of the discharge space of the former is better than the latter.This also provides theoretical basis for the application of mesh electrodes in plasma surface modification.Finally,the appropriate mesh size(L=0.26mm)was selected and apply the mesh—to—plane DBD to modified the surface of PP samples.Hydrophilic property and dyeability of the PP samples is greatly improved when treated by mesh—to—plane DBD plasma,When the plasma treated PP samples were observed by scanning electron microscopy(SEM),The plasma etching phenomenon appeared on the surface of the treated sample,The surface roughness is significantly increased,thereby improving its hydrophilicity.The chemical analysis of the plasma treated PP surface was carried out by Fourier transform infrared spectroscopy.Found that a number of hydrophilic groups were introduced into the surface of plasma treated PP samples,such as:N—H?—OH.The time effectiveness of the treatment effect by mesh—to—plane DBD plasma is weak,After exposing a few days in the air,the absorption peak of the hydrophilic group decreases and the surface hydrophilicity also decreases significantly.