  There is a growing interest in the study of coupled plasma-liquid systems
because of their applications to biomedicine, biological and chemical
disinfection, agriculture, and other areas. Without an understanding of the
near-surface gas dynamics, modellers are left to make assumptions about the
interfacial conditions. For instance it is commonly assumed that the surface
loss or sticking coefficient of gas-phase electrons at the interface is equal
to 1. In this work we explore the consequences of this assumption and introduce
a couple of ways to think about the electron interfacial condition. In one set
of simulations we impose a kinetic condition with varying surface loss
coefficient on the gas phase interfacial electrons. In a second set of
simulations we introduce a Henry's law like condition at the interface in which
the gas-phase electron concentration is assumed to be in thermodynamic
equilibrium with the liquid-phase electron concentration. It is shown that for
a range of electron Henry coefficients spanning a range of known hydrophilic
specie Henry coefficients, the gas phase electron density in the anode can vary
by orders of magnitude. Varying reflection of electrons by the interface also
has consequences for the electron energy profile. This variation in anode
electron density and energy as a function of the interface characteristics
could also lead to significant variation in near-surface gas chemistries when
such reactions are included in the model; this could very well in turn affect
the reactive species impinging on the liquid surface. We draw the conclusion
that in order to make more confident model predictions about plasma-liquid
systems, finer scale simulations and/or new experimental techniques must be
used to elucidate the near-surface gas phase electron dynamics.
