Charge Dynamics and Flashover Performance on Polyethylene Surfaces Modified by Atmospheric Pressure Fluorocarbon Plasma Jet

Abstract

Dynamic surface charge is a critical factor in the flashover of polymer insulating materials, significantly affecting the reliability of electrical and electronic equipment. Fluorocarbon plasma modification tailors surface properties by attaching fluorine-containing functional groups, thereby optimizing charge transport and enhancing dielectric performance. Direct observation of the dynamic behavior of surface charges under applied electric fields provides crucial insights for elucidating how modification improves surface dielectric strength and for optimizing modification parameters. In this study, a needle-ring atmospheric pressure plasma jet (APPJ) using helium and perfluoropolyether (PFPE) was adopted to fluorinate low-density polyethylene (LDPE) films. The effects of He/PFPE APPJ modification on flashover voltage, dynamic charge behavior, surface physicochemical state, surface resistivity, and trap distribution were investigated. The flashover voltage exhibited a non-monotonic dependence on treatment time, initially increasing and then decreasing, peaking at 9.59 kV after 120 s of treatment, representing a 43.35% increase over the untreated sample. Pockels-effect measurements showed that both positive and negative charges were distributed over a wider area after modification, indicating more homogeneous surface charge distribution and faster charge dissipation. A fluorocarbon layer was formed on the LDPE surface, leading to decreased surface resistivity and non-monotonic evolution of shallow and deep trap densities. The surface potential decay rate reached its maximum at 120 s. These results suggest that moderate modification is correlated with a favorable balance between charge transport and trapping, which contributes to improved flashover performance. In contrast, excessive treatment was associated with the rebound of deep trap density and the increased presence of highly electronegative fluorinated groups, which may promote charge retention and partially reduce the flashover voltage. This study provides direct visualization of treatment-time-dependent surface charge dynamics and offers mechanistic insight into the correlation between fluorocarbon plasma modification, surface charge behavior, and flashover performance.