Comparative studies on the structure and diffusion dynamics of aqueous and nonpolar liquid films under nanometers confinement

Aqueous hydration water confined between two mica surfaces and nonpolar liquid argon confined between two solid crystals have been comparably studied through molecular dynamics simulations. A liquid-vapor molecular ensemble developed in previous studies (Leng 2008 J. Phys.: Condens. Matter 20 354017) has been used to investigate the solvation structures and diffusion dynamics of confined films. We find that water always tends to diffuse even under two-layer extreme confinement (D = 0.73 nm), whereas liquid argon undergoes a spontaneous liquid-to-solid phase transition at an appreciable large distance (n = 9 layers) between the two crystal solids. Vacancy diffusion in the solid phase of argon is observed. We attribute this phase transition of argon to the tendency of argon molecules to form a close-packed structure to maximize the cohesion energy contributed from weak van der Waals attractions.