Characteristics of Needle-Disk Electrodes Atmospheric Pressure Discharges Applied to Modify PET Wettability

In the atmospheric pressure discharge with arrangement of a syringe needle, a capillary, and an external disk, it was observed different operation modes according to the relative position of the electrodes. With external electrode over the shaft of the needle, a stable and steady plume is formed from the tip of the needle to the exterior of the capillary. The breakdown is governed by filamentary discharges that evolve randomly on time in the gap between the needle and the capillary. This mechanism changes to bullet-like discharge when the external disk is located off needle. The breakdown generates a large amount of charge that rises quickly and varies with the distance between the electrodes. The mean power is higher than that of the previous case and the plume generated, in interaction with external metallic surface, is more unstable to arc transition. Independently of the operation mode, high electric field at the bevel of the needle plays an important role on the evolution of the plume. The application of the plume to change the wettability properties of the polyethylene terephthalate indicated rapid augment of the hydrophilicy and treated area larger than the plume dimension.