Read the article entitled "Oriented Growth of Calcite Controlled by Self-Assembled Monolayers of Functionalized Alkanethiols Supported on Gold and Silver" by J. Aizenberg, A. J. Black, and G. M. Whitesides (J. Am. Chem. Soc., 1999, 121, 4500-4509) and answer the following questions. What is a self-assembled monolayer? What interactions promote the self-assembly? What interactions promote binding of the alkanethiol to the Ag or Au substrate? What interactions are responsible for binding the calcite to the alkanethiol? Why do some alkanethiols promote crystal formation and others do not? Why is there orientation control of the crystal formation?
Answers:
A self-assembled monolayer arises when molecules bind to a surface in an orderly array that is a single molecule thick. A variety of interactions can be used to induce self-assembly. For the surfaces described in the article, the alkane thiols self-assemble primarily due to van der Waals interactions but the binding to the Ag or Au substrate is debatable, but probably has a large degree of covalency contributing. In this work the authors put ionic groups at the end of the alkanethiol chain to induce the crystallization of the calcite form of calcium carbonate. Thus, the interaction at the calcite/surface interface is ionic.
The mechanism of action for crystal growth and orientation control is certainly debatable. The authors work showed crystal growth only for anionic or neutral surfaces. To me, this suggests that crystal growth is promoted when the first calcite layer is Ca2+, which is small and can get close to the surface easily. Whether the authors "controlled" the orientation of crystal growth or merely observed differences for different surfaces is largely semantics.