Controlling Electron-impact Reactivity at the Gas-liquid Interface through the Shape of the In-liquid Electrode*

     Atmospheric pressure plasmas (APPs) can efficiently activate liquids through various pathways – electron and ion impact, photoionization, photodissociation, and solvation of plasma-produced species.  Liquid activation can lead to the formation of nanoparticles in electrolytic solutions, or the removal of unwanted chemicals, such as PFAS molecules in water. In the case of PFAS removal, remediation efficiency is tightly coupled to electron fluences from the plasma onto the liquid surface, where PFAS molecules are concentrated due to their hydrophobic tails. In this work, we discuss results from a computational investigation of customizing electron fluences in APPs onto liquid surfaces.  We show that the design of the ground electrode in the liquid can significantly affect the plasma properties at the gas-liquid interface. This investigation was performed using the nonPDPSIM modeling platform, which addresses multiphase (gas and liquid) plasmas.  The test system is a negative pulsed plasma jet onto water with a fluorocarbon surfactant layer.  By shaping the in-liquid electrode into sawtooth structures, the electron-impact reactivity onto the surface can be strongly enhanced (or decreased) in regions where the ground is closer (or further) to the gas-liquid interface. The local increase in electron density and temperature may be used to activate nonlinear reaction paths consisting of several steps.  Dissociation rates of the surfactant molecule are used to demonstrate these trends.