Interaction of atmospheric pressure plasma jet with a dielectric surface: relative permittivity and roughness

Atmospheric pressure plasma jet (APPJ) has been widely studied for its unique advantages in material surface processing. The exploration of the interaction mechanism between APPJ and material surface is helpful to optimize the surface treatment. In this paper, a 2D axisymmetric fluid model is used to simulate the interaction between APPJ and the dielectric surface driven by negative DC voltage. The effects of the relative permittivity (epsilon r) and roughness of the surface on the evolution of the discharge on the surface of the dielectric are investigated. In this paper, the wave surface composed of semicircles with different radii (R = 0.1 mm, 0.3 mm, 0.5 mm) represents the uneven surface with different roughness, and three sets of values with epsilon r of 1.2, 5 and 80 are selected for simulation. The results show that with the increase of epsilon r, the ionization region shrinks to the center, from a ring region to a solid circular region. When epsilon r increases to 5, corona discharge begins to appear at the central troughs of the dielectric surface. In addition, epsilon r and R together affect the propagation modes of the ionization wave in the grooves in the radial region. With the increase of epsilon r and the decrease of R, the propagation direction of ionization waves in the grooves is reversed. For the distribution of reactive species used to modify the surface of the material, as epsilon r increases, the treatment area begins to shrink toward the center. In addition, the smaller the R, the more uniform the fluxes of reactive species. Therefore, for material surfaces with different epsilon r or R, the modification site, the processing depth and intensity by active particles will change due to changes in the evolution process of APPJ.