Why Does Plasma Induced Flow of Saline Change Direction Over Time?

Controlling plasma induced liquid flow (PILF) is thought to be a crucial step towards complete control of the distribution of plasma-produced species through a bulk liquid, and thereby improving the efficiency of plasma-liquid interactions. When a plasma jet impinges on de-mineralised water (DW), PILF is directed upwards directly below the plasma-liquid interaction point in the so-called “upwards regime”. When saline is used however, PILF is directed downwards from the interaction point, in the “downwards regime”. The inverse direction of PILF in saline has time dependence, where over several minutes we observe experimentally a transition towards the upwards regime with similar intensity to that observed in DW. We demonstrate in a study that downwards regime flows in saline are due to liquid phase electro-hydrodynamic forces, not present in DW, and that the time dependent flow reversal is likely due to plasma electrolysis.