The Electrostatic Debye Layer Of The Plasma-Liquid Interface

New uses for low-temperature plasma, such as plasma medicine and various chemical synthesis techniques, require a fundamental understanding of the plasma-liquid interface for further development. In this work, we have derived and tested an analytic model for the electrostatic Debye layer formed at a plasma-liquid interface. The theoretical model combines the Gouy-Chapman theory of aqueous electrolytes with a simple parabolic band model for the plasma sheath, and it gives closed form expressions for the electric field and charge distribution at the interface. It also predicts the plasma current density as a function of the solution ionic strength, which we experimentally confirmed using a liquid anode plasma. Fitting the model to the experimental data yields a plasma electron density of ~1019 m-3 and an electric field of ~104 V/m on the liquid side of the interface. Since the Debye layer is such a universal phenomena, we believe that our model can be extended to other plasma-liquid systems such as DBD and RF jets.