Entropy Effect in Ice Crystal Nucleation

Abstract

The effect of bond orientation in ice, which leads to its residual entropy, is also found to be important in its heterogeneous nucleation. Any substrate which orients ice dipoles at its surface parallel to one another is a poor nucleating atent, because it reduces the entropy and hence raises the free energy of any small embryos growing upon it. Critical temperatures are calculated for surfaces of this type, and it is shown that for crystals like AgI or PbI2 the basal faces are poor ice crystal nuclei, and activity is mostly confined to the prism faces. This result leads to improved agreement between observed and theoretical nucleation thresholds and gives an explanation of some of the phenomena observed in nucleation by monocrystalline substrates.