Influence of Metal Surfaces on the Efficiency of Ice Nucleation

Ice crystal characteristics, such as number, size, and shape, in clouds influences their optical properties and the radiation balance of our climate. In the atmosphere, aerosol particles can interact with water and form ice crystals, known as heterogeneous ice nucleation, which is more efficient than homogeneous ice nucleation where ice nucleation occurs with no solid particle. Heterogeneous ice nucleation activity depends heavily on the surface of its nucleus. However, the ice formation process on these surfaces is generally not well understood. In this study, two types of experiments were performed: one in which the surface functionalization of silver nanoparticles was studied and another in which the extended hydration of hematite and goethite, iron oxide minerals, was explored. Immersion freezing was completed on both systems to compare the ice nucleation efficiency. We found that bare silver nanoparticles appear to be the most efficient nucleus in ice nucleation in comparison to the two sets of functionalized silver nanoparticles with 11-mercaptoundecanoic acid (11-MUA) and p-phenylenediamine (p-PDA). It appears that both iron oxides become noticeably less efficient in ice nucleation after one day of processing in water. Increased mixing time likely creates smaller particles as they collide; thus, the smaller surface areas for ice nucleation may inhibit efficiency of freezing. A better understanding of ice nucleation could lead to advances in fields such as weather and climate modeling.