Spontaneous formation of nanopores within a nanofilm: Phase diagram and multiple stable states

Spontaneous formation of a nanopore within a liquid nanofilm immersed in a solvent was explored by many-body dissipative particle dynamics simulations. The nanofilm is sandwiched between two plates with circular orifices. As the liquid amount in the nanofilm changes, the menisci of the nanofilm near the orifices will be altered accordingly. The state of the nanofilm depicted by the mean curvature (H) of the meniscus depends on the apparent density (ρ_a) of the film and four regimes can be identified: (I) bulged film, (II) symmetric indented film, (III) asymmetric indented film, and (IV) nanopore formation. In the former two regimes, two identical convex (I) or concave (II) menisci are formed near the orifices. As ρ_a decreases further, the concave menisci are different on both sides of the nanofilm (III), and eventually the axis-symmetric nanopores (IV) emerge spontaneously. The relationship between H and ρ_a is not monotonous and involves minimum, maximum, and plain. As a result, multiple stable states are observed at the same Laplace pressure (ΔP) which relates to the mean curvature by the Young-Laplace equation. At a specific ΔP, the nanopore develops at lower ρ_a, while the indented film appears at higher ρ_a.