ORGANIC TEMPLATE-DIRECTED INORGANIC CRYSTALLIZATION - ORIENTED NUCLEATION OF BASO4 UNDER COMPRESSED LANGMUIR MONOLAYERS

Langmuir monolayers of n-eicosyl sulfate were shown to influence the nucleation of BaSO4 grown from supersaturated solutions (S = 30) at room temperature (293 K). Thin, elongated single crystalline plates were nucleated with the (100) face parallel to the plane of the monolayer. Partial matching of cation-cation distances with the interheadgroup spacings and stereochemical complementarity between the anionic motif and sulfate headgroups are potential factors responsible for oriented nucleation. The oriented crystals exhibited an unusual texture of coherently intergrown rhombic subunits which was attributable to monolayer-induced growth along specific lattice directions parallel to the monolayer/solution interface. By contrast, barium sulfate crystals nucleated under compressed eicosanoic acid monolayers were oriented along the [010] direction. These crystals were irregular in morphology, suggesting a kinetic rather than a structural influence of the organic template on nucleation at the monolayer/solution interface.