(286c) Effect of Multivalent Surface Cations on Heterogeneous Freezing of Water

Heterogeneous ice nucleation is a crucial phenomenon in various fields of fundamental and applied science. In this study we investigate the effect of surface cations on freezing of water on muscovite mica. The exposed ion on mica’s surface can be exchanged without affecting other properties such as surface roughness. We investigate freezing of water on natural (K+) mica and mica surfaces where K⁺ is for Al³⁺, Mg²⁺, Ca²⁺, and Sr²⁺. We mica surfaces with ions of higher valency exposed are better ice nucleators; i.e. nucleation on Al³⁺-mica surface occurs at higher temperatures than the mica surfaces with divalent ions. Molecular dynamics simulations indicate that multivalent cations enhance the probability of forming larger clusters of hydrogen bonded water molecules. The cations provide anchors for these clusters. These clusters could provide seedbed for ice nuclei. This represents a novel mechanism through which ions can enhance ice nucleation. The results of the combined experimental and simulation studies shed new light on the influence of surface ions on heterogeneous ice nucleation.