The effect of air solubility on the Kapitza resistance of the copper-water interface

We perform a calibration of the force fields between copper, water, and air based on experimental parameters, such as the value of the water contact angle on a bare copper surface, the bulk density and thermal conductivity of water and air. Besides, the air solubility in water is estimated at different pressures and temperatures. Using nonequilibrium molecular dynamics (NEMD) simulations, we investigate the effect of the air on Kapitza resistance at high pressure in a copper-water-air system. The results show that a thick air layer at the copper-water interface reduces the ordering of the water layers adjacent to the copper surface, and is responsible for an increase in the Kapitza resistance. Moreover, we find that high pressure can induce highly-ordered water layers that significantly promote the phonon transport across the solid-liquid-gas interface, which leads to the reduction of the Kapitza resistance. Furthermore, we analyze the normalized copper-water Kapitza resistance / for different gas solubilities and pressures. Here, denotes the effective Kapitza resistance between copper and water, where the temperature jump is approximated by the temperature difference across the air layer. is the Kapitza resistance at ambient pressure in the copper-water system without air. The normalized Kapitza resistance suggests that higher pressures can reduce the contribution of the thickness of the air layer on the increase of Kapitza resistance. We propose a simple model for the effective Kapitza resistance taking into account a thin air layer at the solid-liquid interface. At ambient conditions, the model predicts a 3-fold increase in the Kapitza resistance for a 1 nm thick air layer.