Plasma-liquid interactions on acoustically structured Faraday liquid interfaces

Abstract

Enhancing reactive species transport at the plasma-liquid interface is important for scaling of atmospheric pressure plasmas studied in the laboratory to real-world applications. It is well-known that the introduction of turbulence at any interface will enhance mixing by enhancing species uptake from the gas phase to the liquid phase by surface renewal processes, entrainment, bubbles and surface area modification. The goal of this work is to isolate surface effects associated with turbulence from the multitude of turbulent transport enhanced processes by artificially introducing surface perturbations using Faraday waves. Experiments were conducted to determine decoloration rate constants of a model contaminant (methylene blue) as a function of both discharge features (including positive and negative streamers) and hydrodynamics (Faraday surface wavelengths). The local plasma ionization wave at the interfacial structure was modeled and compared to experiments. Interestingly, it was found in experiments that plasma in contact with the water also generated capillary waves thus modifying the surface as well. Plasma ionization waves in combination with acoustic driven Faraday waves adds to the complexity of interpreting the effects of, for example, surface area increases, due to these complex coupled phenomenon. Local plasma ionization wave structure appears to be modified (increased propagation distance) when the liquid is perturbed, leading to increased contact of the liquid water surface with reactive species. Along with interfacial surface area growth, nonlinear convective transport is also increased with perturbations, leading to the general realization that acoustic perturbations can improve transport and thus decoloration of the model contaminant dye.