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Study Investigates Effect of Surface Defects on Heterogeneous Ice Nucleation

The heterogeneous ice nucleation process induced by ice nucleation particles (INPs) such as mineral dust and organic material is the most common mechanism of ice formation in nature and plays an important role in cloud formation. The mechanism of heterogeneous ice nucleation depends on the balance between surface morphology and hydrophobicity.

The presence of a seed particle can significantly reduce the supercooling needed for freezing water compared to homogeneous nucleation. Small particles of silver iodide (AgI) are known to be effective INPs and have been used in various cloud seeding applications. AgI particle have been extensively studied both experimentally and computationally, focusing on ice nucleation on AgI surfaces.

Professor Hannele Korhonen, the Director of the Climate Research Program at Finnish Meteorological Institute and a second cycle awardee of the UAE Rain Enhancement Program (UAEREP) worked on a project to investigate how the presence of defects on AgI (0001) surfaces affects ice nucleation and growth rates.

In her work, Professor Hannele Korhonen used molecular dynamics (MD) simulations to study the effect of surface defects, such as vacancies, step edges, terraces and pits, on the heterogeneous ice nucleation on AgI (0001) surfaces.

Using atomistic molecular dynamics simulations, the study analyzed snapshots of the MD trajectories taken at every nanosecond to classify each H2O molecule as either cubic ice, hexagonal ice, interfacial ice, or liquid, based on its hydrogen bond arrangement.

The simulation results show that the AgI (0001) surface enhances the formation of a critical nucleus by enforcing its hexagonal structure to the first hydration layer. The results also found that the growth of ice essentially proceeds layer by layer once the nucleus has covered the entire interface.

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