INFRARED SPECTROSCOPIC AND CHEMICAL ETCHING STUDY ON THE CRYSTALLIZATION PROCESS OF THE B-FORM AND E-FORM OF STEARIC-ACID - ROLES OF DISLOCATIONS IN SINGLE-CRYSTALS

Crystallization processes of B and E forms of stearic acid were investigated by means of infrared spectral measurement and microscopic observation. Polymorphic and polytypic transformations took place during the crystal growth in a solution. The single-layered polytype of the E form was generated at first, and the overgrowth of the double-layered polytype of E took place on the (001) face of the single-layered one. The polymorphic transformation from E to B occurred for specific single crystals. The single crystal of B grew as a single-layered polytype in the initial stage, consuming crystals of the unchanged E crystals through solution-mediated phase transformation. In the chemical etching experiment, the crystals that had been transformed to B quickly exhibited many etch pits due to screw dislocations on the (001) face, whereas there were very few pits on the unchanged crystals. This fact strongly suggests that the E --> B transition would proceed in one single crystal along the spiral structure due to screw dislocations.