Modelling of Acoustically Structured Plasma-Liquid Interfaces

Plasmas interacting with liquid surfaces produce a complex interfacial layer where the local chemistry in the liquid is driven by fluxes from the gas phase of electrons, ions, photons, and neutral radicals. Typically, the liquid surface has a mild curvature with the fluxes of impinging plasma species and applied electric field being nominally normal to the surface. With liquids such as water having high dielectric constant, structuring of the liquid surface by producing a wavy surface enables local electric field enhancement due to polarization of the liquid, as well as producing regions of higher and lower advective gas flow across the surface. This structuring (or waviness) can naturally occur or can be achieved by mechanical agitation such as with acoustic transducers. Electric field enhancement at the peaks of the waves produce local increases in sources of reactive species and incident plasma fluxes. In this paper, results are discussed from a computational investigation of pulsed atmospheric pressure plasma jets and pulsed plasmas in air onto structured liquid water surfaces consisting of standing wave patterns having wavelength and wave depth of hundreds of microns to 1 mm. The potential of structured liquid surfaces to enhance nanoparticle synthesis in the context of plasma driven solution electrochemical applications will be discussed.