THE STRUCTURE AND PROPERTIES OF MELT AND CONCENTRATED-SOLUTIONS

The crystallization process is determined by the properties of the sol id and of the properties of the liquid state. The properties of the so lid at the melting temperature T(m) can be scaled by so-called melting rules. These rules are based on the similarity laws of interatomic fo rces and provide scaling laws for substances with similar crystal latt ices and similar molecular bonds. Scaling laws can also be developed f or the properties of simple liquids. Their applicability is more limit ed, because most liquids are not simple liquids. Their application to crystal growth is even more limited because a crystal does not grow in to bulk liquid but into a surface layer. This surface layer has always long range correlations. Long range correlations in liquids and surfa ce layers lead to density fluctuations. Light scattering is a powerful tool to study density fluctuations. The most important results from l ight scattering experiments during crystal growth are: The solid- liqu id interface is not sharp. There is a thick (mum) layer of preordered material in front of the growing crystal. The crystal grows into the i nterface layer - not into bulk melt. The diffusion constant for the mo lecules in the solid- liquid interface layer is much smaller than the constant of self diffusion in the melt. Light scattering is a useful t echnique-for the study of the dynamics of the solidification process a nd for the characterization of crystal surfaces.