Unraveling the Mechanism of Ice Nucleation by Mica (001) Surfaces
Abhishek Soni, G. N. Patey
Abstract
Heterogeneous ice nucleation is an important process in atmospheric science, food preservation, and other areas of research. Muscovite mica is a commonly occurring mineral, and although its ice nucleating ability has been widely debated, recent experiments have established that some mica (001) surfaces efficiently nucleate ice. We employ molecular dynamics simulations to investigate ice nucleation by three variations of the mica (001) surface. These are bare surfaces devoid of counterions (B-mica), surfaces with ordered arrangements of K+ counterions (K-mica), and protonated surfaces (H-mica). Our simulations show that B-mica and H-mica effectively nucleate ice, but K-mica does not. For B-mica and H-mica, the ice nucleation mechanism is unusual in that it does not occur via the basal or prism plane of Ih. The mica (001) surfaces stabilize an ice bilayer resembling (but not identical to) the pyramidal (202̅1) plane of Ih. This results in a mixed-phase ice nucleus consisting of hexagonal and cubic ice layers stacked in a particular order imposed by the surface. We discuss in detail the connections between surface composition, morphology, and ice nucleation. The influence of finite system size on ice nucleation is also investigated. Finally, we discuss our simulations in view of recent experimental results. Taken together, the experiments and simulations cast new light on ice nucleation by mica (001) surfaces.