Confined water in hydrophobic nanopores: Dynamics of freezing into bilayerice

Molecular dynamics simulations for a thin film of water confined to a slit nanopore are performed in order to investigate the dynamic process of cryst allization of the system. The system upon freezing creates a bilayer ice cr ystal composed of two layers of hexagonal rings. We perform one simulation at T = 257 K during which the system remains a supercooled liquid state, an d another one at T = 253 K during which the system freezes. Many patterns o f molecular arrangement are found upon freezing, and an account is given of the origin of multiple peaks in the distributions of binding energy and pa ir interaction energy. A definition of the solidlike cluster is introduced in order to analyze the time evolution of the clusters' population and thei r shapes. A large variety of shapes including highly nonspherical ones can be detected during simulations. A steady population of clusters is found at T = 257 K, whereas at T = 253 K a post-critical nucleus of the solid phase emerges within a few nanoseconds and continues to grow until the system fr eezes completely. [S1063-651X(99)13411-1].