A computational investigation of the phase behavior and capillary sublimation of water confined between nanoscale hydrophobic plates

Thin films of water under nanoscopic confinement are prevalent in natural and manufactured materials. To investigate the equilibrium and dynamic behavior of water in such environments, we perform molecular dynamics simulations of water confined between atomistically detailed hydrophobic plates at T = 298 K for pressures (-0.1) ≤ P ≤ 1.0 GPa and plate separations of 0.40 ≤ d ≤ 0.80 nm. From these simulations, we construct an expanded P-d phase diagram for confined water, and identify and characterize a previously unreported confined monolayer ice morphology. We also study the decompression-induced sublimation of bilayer ice in a d = 0.6 nm slit, employing principal component analysis to synthesize low-dimensional embeddings of the drying trajectories and develop insight into the sublimation mechanism. Drying is observed to proceed by the nucleation of a bridging vapor cavity at one corner of the crystalline slab, followed by expansion of the cavity along two edges of the plates, and the subsequent recession of the remaining promontory of bilayer crystal into the bulk fluid. Our findings have implications for the understanding of diverse phenomena in materials science, nanofluidics, and protein folding and aggregation.