Surface Energy-Mediated Multistep Pathways for Heterogeneous Ice Nucleation

Heterogeneous ice nucleation (HIN) is the dominant mode of ice formation, while its kinetic pathways remain poorly understood. The classical nucleation theory suggests a one-step pathway, that is, direct change from liquid water to ice (e.g. hexagonal ice), which has been widely accepted. In this work, however, through molecular dynamics simulations, we observe an intermediate state, square ice, at the early stage of ice nucleation at certain surface energies. The intermediate square ice gives rise to a new nonclassical pathway for HIN: from liquid water to hexagonal ice via square ice. This multistep pathway may coexist with and can be more probable than the classical one-step pathway though it may delay the ice nucleation process. The new multistep pathway offers insights in controlling the kinetics of ice crystallization and understating the mechanisms of HIN

Roles of Surface Energy and Temperature in Heterogeneous Ice Nucleation

Heterogeneous ice nucleation (HIN) is strongly related to the dynamics of hydrogen bonds in water at an interface. In this work, we investigate the microscopic kinetics of HIN through molecular dynamics simulations. The dynamics of hydrogen bond network (HBN) at interfaces is studied under the coupled effects of thermal fluctuation and water–surface molecular interactions. It is revealed that the lasting time of the HBN at the interface is critical to HIN. Under comparable thermal and surface effects, which result in a proper lasting time of the HBN, HIN is promoted. However, if the thermal effect or the surface effect dominates over the other, the lasting time of the HBN at the interface would be either too long or too short, leading to the failure of HIN. By varying the water–surface interaction strength, i.e., binding energy, and temperature, a diagram of HIN events is presented, which shows that HIN is only favored in certain temperature and surface energy ranges