Molecular dynamics simulation of the liquid-vapor interface of TIP4P/2005 water with coumarin 314 molecules: Effect of solute molecules on evaporation mass flux

Evaporation plays an essential role in a wide range of industrial applications, such as cooling devices using evaporation from porous array membranes. The heat removal performance of such devices is determined by evaporation mass flux. The Hertz-Knudsen equation is often used to estimate evaporation mass flux at liquid-vapor interfaces. This equation includes the evaporation and condensation coefficients, which are unknown parameters that must be determined from experiments. However, these coefficients reported so far are scattered over three orders of magnitude for an identical liquid and temperature. This variation is presumed to originate from impurities (solute molecules) at a liquid-vapor interface, although the effect of solute molecules at the liquid-vapor interface on the evaporation and condensation coefficients has yet to be fully clarified. In the present study, molecular dynamics simulations were conducted to quantify the effect of solute molecules at a liquid-vapor interface on evaporation mass flux. We constructed a model of the liquid-vapor interface of an aqueous solution of coumarin 314 and simulated evaporation at 300-500 K. We quantified the relationship between the evaporation mass flux and the surface density of the solute molecules.