High density gas state at water/graphite interface studied by molecular dynamics simulation

In this paper molecular dynamics simulations are performed to study the accumulation behaviour of N_2 and H_2 at water/graphite interface under ambient temperature and pressure. It finds that both N_2 and H_2 molecules can accumulate at the interface and form one of two states according to the ratio of gas molecules number to square of graphite surface from our simulation results: gas films (pancake-like) for a larger ratio and nanobubbles for a smaller ratio. In addition, we discuss the stabilities of nanobubbles at different environment temperatures. Surprisingly, it is found that the density of both kinds of gas states can be greatly increased, even comparable with that of the liquid N_2 and liquid H_2. The present results are expected to be helpful for the understanding of the stable existence of gas film (pancake-like) and nanobubbles.