OPTICAL STUDY OF SURFACE MELTING ON ICE

We have used an optical reflection technique to measure the thickness of water films existing on the surfaces of isolated single H2O ice crystals, at temperatures below 0-degrees-C. The crystals were grown in situ from pure water vapor. When investigated under these conditions the water films were found to be of finite thickness at all T up to and including the triple point, indicating incomplete wetting of water on ice, or incomplete surface melting. The maximum film thickness detected was approximately 200 angstrom. At T(TR) water drops appeared on the ice facets, observed by interference microscopy. Their contact angles were consistent with the above findings. The addition of air to the atmosphere caused the film thickness to diverge on some orientations of the surface, i.e. it caused complete wetting or complete surface melting.