Studies of Ice- Vapour Surfaces and Interfaces

Abstract

Four separate studies of interfacial phenomenon of ice crystals are presented. The ice-gas interface was explored using ellipsometry and it was found to have a thin water layer wetting the interface above T ≈ -10°C. The thickness of the ice-air inter-layer started to diverge logarithmically up to T ≈ -1°C to about l0nm but then underwent a smooth transition to an incomplete wetting regime as T → 0°C . The same qualitative behaviour occured when CO2 or vapour of the liquids methanol,. dichloroethane and pentane were added to the gas phase. The hydrocarbons were introduced at near their saturation vapour pressures. Methanol and dichloroethane appear to produce thicker water layers than the other species. The second study measured the contact angle at the ice-water-vapour line. Contact angles close to zero were observed in close to equilibrium conditions, the average contact angle being independent of crystal anisotropy and slightly greater for measurements obtained in air as opposed to vapour. The third study looked at internal melting of ice, where millimetre sized hexagonal liquid regions develop in irradiated ice. They were found to increase in number when the ice in which they grew had itself been grown more rapidly. This was independent of irradiation level. This supports the hypothesis that microscopic gaseous inclusions nucleate internal melting. The fourth study observed the liquid dendrites of these internal melt figures and found them to satisfy the "solvability theory" of dendritic growth forms with the exception of anomalously large secondary (sidebranch) dendrites wavelengths.