Thermodynamics of epitaxial calcite
nucleation on self-assembled monolayers
Travaille
AM, Steijven EGA, Meekes H, van Kempen H
J.
Phys. Chem. B 109 (2005) 5618-5626
Abstract:
Classical heterogeneous nucleation theory is used to describe the
epitaxial nucleation of calcite on self-assembled monolayers (SAMs).
Both spherical and faceted clusters are considered. The use of faceted
clusters reveals a useful relation between the shape of very small
crystals and the ratio of the heterogeneous and homogeneous nucleation
barriers. The experimental approach of this paper concerns the
measurement of the threshold driving forces for both homogeneous and
heterogeneous nucleation of calcite. This is accomplished by preparing
solutions with well-defined driving forces and by measuring the
resulting types of nucleation that are observed after a fixed
experimental time. The results of the experiments and the theoretical
shape analysis are compared, and it is shown that in the experiments no
homogeneous nucleation of calcite occurs for driving forces up to at
least Delta mu/k(B)T approximate to 6.0. A calculation of the critical
cluster size for heterogeneous nucleation results in a range of 2-28
growth units and faceted critical clusters from 3-28 growth units,
depending on the value of the surface free energy of calcite. These
sizes are 50-100 times smaller than the crystalline domain sizes of
SAMs and therefore small enough to explain the promoting effect of the
substrate.