The surface charge distribution affects the ice nucleating efficiency of silver iodide.

Abstract

Heterogeneous ice nucleation is the primary pathway for ice formation. However, the detailed molecular mechanisms by which surfaces promote or hinder ice nucleation are not well understood. We present results from extensive molecular dynamics simulations of ice nucleation near modified silver iodide (AgI) surfaces. The AgI surfaces are modified to investigate the effects of the surface charge distribution on the rate of ice nucleation. We find that the surface charge distribution has significant effects on ice nucleation. Specifically, AgI surfaces with the positive charges above the negative charges in the surface promote ice nucleation, while ice nucleation is hindered for surfaces in which the negative charges are above or in-plane with the positive charges. The structure of water molecules in the interfacial region as measured by the orientations of the water molecules relative to the surface can explain the differences in the ice nucleation at the different surfaces. We suggest that the distributions of the orientations of the interfacial water molecules could be used more broadly as a measure of ice nucleating propensity.