Computer modelling of the interface between alcohols and the (10.4) calcite surface

Crystals grown in organic or biological environments
often show more complex morphologies than those generated
using more conventional methods. For this reason techniques
allowing control of the size and shape of crystal growth in
organic solutions are of current industrial and academic
importance. However, there still remains uncertainty over
the exact mechanisms by which these processes progress.
Computer modelling provides one route to improving our
understanding of these processes.

In this work we report initial results modelling the
interaction between alcohol solutions and the (10.4) surface of
calcite, which dominates the morphology of conventionally
grown crystals, expanding on previous studies undertaken in
this area. The DL_POLY 2 molecular dynamics package
has been used to simulate several alcohol-calcite systems.
These simulations, and subsequent analysis, suggest that an
increase in the carbon chain length of the alcohol results in a
decrease of the interfacial energy, which infers that the longer
chain alcohols are therefore less tightly bound to the calcite
surface.

Analysis of the radial distribution functions (RDF),
demonstrates that the distance between the surface Ca ions and
the alochol oxygen in the adsorption layer is approximately
1.5 Å and the separation between the CO3 oxygen and the –
OH hydrogen to be around 2.5 Å, demonstrating that the
strong interations exist between the molecules and the surface.

This is further demonstrated when the density profile
perpendicular to the surface is considered, where a highly
ordered adsorption layer is observed together with less well
defined secondary layers further from the surface.

Future work will extend this study to consider the
interface between stepped calcite surfaces and alcohol and will
also consider the co-adsoption of water and alcohol at the
surface.