TEMPLATE-DIRECTED NUCLEATION AND GROWTH OF INORGANIC MATERIALS

The ability to tailor the crystal chemical properties of inorganic solids in a predictable and reproducible manner is attractive to materials scientists and chemists, and chemical engineers seeking to optimize and/or exploit selective I physicochemical features of crystalline materials. The use of water soluble additives to regulate particle size and morphology is a common strategy whereas the potential of organized assemblies of organic molecules to control nucleation and growth has yet to be fully realized. This is largely due to our incomplete understanding of the molecular processes governing the crystallization of inorganic crystals on organized substrates. In this article, we have described how Langmuir monolayers can be adopted as model surfaces because of the opportunities offered by molecular engineering of the template (head group identity, polarity, packing density, etc.). An added advantage is that the structure of these templates is accessibility to several sensitive surface analytical techniques such as grazing angle neutron and X-ray diffraction. A range of template/subphase combinations have now been investigated and it is clear that one theme-that oriented inorganic nucleation can be controlled by molecular recognition between the two-dimensional organic template and embryonic inorganic aggregates-is common to them all. To date, these studies, and related work with soluble additives, have focused attention upon the importance of structural. stereochemical, and dynamical relationships to these recognition processes. As with the majority of such host-guest interactions that operate on a molecular scale, specificity is critically dependent upon the interplay of many factors, often with only small energy differences between alternative mechanistic pathways. We are only just beginning to explore this new horizon of materials chemistry, and many surprises are in store.