Discharge Regime Selection Governed by Liquid Conductivity and Configuration in a Liquid–Gas–Liquid Plasma System

Plasma discharges at gas–liquid interfaces generate reactive species directly in liquids, but conductivity‐ and configuration‐dependent regime selection under pulsed excitation remains unclear. Here, metallic electrodes were immersed in liquids separated by a gas gap. Varying the conductivity and arrangement of phosphate‐buffered saline (PBS) and ultrapure water (UPW) yielded two discharge regimes. PBS–PBS exhibited a spark‐to‐DC‐glow transition with pronounced interfacial heating and enhanced chemical production, whereas UPW‐containing systems showed dielectric‐barrier‐discharge‐like behavior with transient streamers, minimal gas heating, and weaker post‐discharge chemical responses. A conductivity‐matched NaCl–NaCl solution reproduced the spark‐to‐DC‐glow transition. These findings identify liquid conductivity and cathode/anode arrangement as key determinants of discharge‐regime selection and associated optical, thermal, and post‐discharge chemical responses.