Aqueous Foams as Templates for the Synthesis of Calcite Crystal Assemblies of Spherical Morphology

The crystallization of calcite in the form of spheroaggregates in aqueous foam stabilized by the surfactant sodium bis-2-ethylhexyl-sulfosuccinate (aerosol OT, AOT) by a method of ion entrapment is described. Reaction of Na₂CO₃ with Ca²⁺ ions electrostatically entrapped in the foam results in the formation of flat, platelike calcite crystals, possibly in the plateau border regions of the foam. Hydrodynamic flow patterns in the foam are believed to transport the calcite platelets from the plateau border regions into the larger plateau junctions where they assemble into spherical structures by hydrophobic association. The large interfacial area of the liquid lamellae in the foam provides an attractive and versatile template for the large-scale synthesis of not only minerals but also other nanoscale materials.