Modelling the interfaces between calcite crystals and Langmuir monolayers

Langmuir monolayers are good model systems for investigating the use of organic templates to control the growth and morphology of calcium carbonate. We investigate the structure of the organic-mineral interface using molecular dynamics methods. The monolayer consists of octadecanoic (stearic) acid molecules; the calcium carbonate is the calcite phase. Seven interfaces were chosen to demonstrate the various types of behaviour possible. We show that simple epitaxial arguments based on the ideal, unrelaxed monolayer and mineral surfaces can be very misleading, particularly when considering polar directions. Furthermore, such arguments cannot predict the relative stability of the various interfaces. We show that the polar (001) direction (with a Ca termination) produces the most stable interface and discuss the implications for mineral growth on organic monolayers.