(433c) How Surface Affects Ice Nucleation: Water On Kaolinite Surface

How surfaces affect the ability of water to freeze into ice is a pivotal question in atmospheric science. Elegant experimental studies clearly show that surfaces have varied effects on ice nucleation: while some surfaces promote ice nucleation and growth, others suppress it. This in turn has implications on cloud physics. However, a clear theoretical understanding of this phenomenon that is important for modeling cloud microphysics is still lacking. We address this challenge by studies aimed at elucidating the molecular behavior underlying surface effects on ice formation. We perform extensive molecular simulation studies of water in contact with kaolinite surface at various temperatures. We also perform simulations containing droplets of water containing kaolinite. These represent the freezing of water on mineral dust surfaces in the clouds. Kaolinite represents a dominant class of mineral dust found in the atmosphere. Kaolinite has two surfaces exposed to water: one is hydrophilic exposing hydroxyl groups to water and the other is hydrophobic with silica atoms in contact with water. We present results that characterize water behavior as well as ice nucleation on both these surfaces. These results provide insights into how various surfaces affect ice nucleation and will aid in developing a more general framework to understand of how surface properties like hydro-phobicity/philicity affect ice nucleation. This understanding will aid in the development of a framework within which heterogeneous nucleation can be incorporated into the present models used to describe cloud formation.