Nucleation mechanism for vapor-to-liquid transition from substrates with nanoscale pores opened at one end.

In this work, we study the nucleation mechanism of vapor-to-liquid phase transition from rough substrates, which are modeled as flat substrates decorated with square nanopores with one open end. Our calculations in a constrained lattice density functional theory shows that the presence of nanopores results in an intermediate state, either metastable or unstable, which divides the whole nucleation process into two sequential sub-processes, i.e., pore filling and phase transition outside the pores. Therefore, the nucleation mechanism was found to be one-step (with unstable intermediate states) or two-step (with metastable intermediate states), depending on the fluid-solid interaction, chemical potential, and pore size. The constructed phase diagram of nucleation mechanism shows that there exist six different nucleation mechanisms. In addition, our calculations show that the presence of nanopores on a rough substrate may change the morphology of critical nuclei from their counterpart on a smooth substrate.