TEMPLATE-DIRECTED INORGANIC CRYSTALLIZATION - ORIENTED NUCLEATION OF BARIUM-SULFATE UNDER LANGMUIR MONOLAYERS OF AN ALIPHATIC LONG-CHAIN PHOSPHONATE

Compressed Langmuir monolayers of an aliphatic long chain (C20) phosphonate were shown to influence the morphology and crystallographic orientation of barium sulfate nucleated from the aqueous subphase. The crystals were aligned with the [ 1001 crystallographic axis perpendicular to the plane of the monolayer indicating that nucleation occurred on the (100) face. The majority of these oriented crystals exhibited a rhombic habit during the initial stages of crystallization. These subsequently developed into platelike or "bow-tie" morphologies depending upon the growth mechanism under the monomolecular film. Occasionally, small polar laths oriented along the [100] axis were observed. For each of these crystal forms, nucleation on the (100) face and their subsequent development can be rationalized in terms of specific electrostatic, geometric and stereochemical interactions at the organic/inorganic interface.