A quantitative study of pattern formation in dendritic crystal growth from supersaturated solution

The patterns formed in dendritic crystal growth can have characteristic length scales considerably larger than any intrinsic scales of the underlying system. These macroscopic scales result from a complex interaction of microscopic and macroscopic dynamics. Recent theoretical work has focused on the relationship between the macroscopic properties of steady state dendritic tips and the underlying microscopic material properties. In particular, the tip speed radius of curvature, and mean initial sidebranch spacing, are predicted to be determined by a solvability condition involving the anisotropy in the surface tension at the solid-liquid interface. These predictions were not tested for any materials prior to this work. The complex structure of the time-dependent sidebranches is also not well understood, and is an important area for research. Experiments on the dendritic growth of NH4Br from supersaturated aqueous solution are reported. Digital image processing is used to perform precise measurements of interfacial contours and to provide a quantitative characterization of the growing patterns. The time-dependence of the sidebranch structure near the tip is characterized.