A Study of the Mechanism of Contact Ice Nucleation

Abstract

The nucleation of freezing of supercooled water drops by metaldehyde, phloroglucinol and 1,5?dihydroxynaphthalene was studied. It was found that the threshold temperature for nucleation by contact of the particles with the supercooled drops was 2?3°C warmer than the threshold when the same drops were melted and re?frozen with the nuclei already partly immersed. There was no evidence that the high threshold for contact nucleation was due to active sites that were subsequently destroyed. Rather, it was thought to be associated with the movement of the water front along the surface of the nucleus during the contact process. It is suggested that this process gives rise to a transient high free energy zone which facilitates nucleation. In support of this theory, measurements were made of the contact angles of water on the three compounds.