New Instabilities in Directional Solidification of Succinonitrile

We report comprehensive measurements of interfacial properties as well as observations of new behavior at the cellular interface in directionally solidifying succinonitrile. Observations of the bifurcation from the planar state in cells thicker than 100micro show that the initial instability occurs first in the direction along the shortest dimension of the cell. This raises questions about the applicability of many conventional descriptions of patterns that rely on two-dimensional diffusive fields.