Calcium carbonate is an important compound in man-made cements as well as in cements used
by several animals and bacteria to produce their skeletons and exoskeletons. The sedimentary
layers of the Earth’s crust is rich in calcium carbonate, making it a globally abundant mineral
being the main constituent in rocks such as limestone, marble and chalk. Animals and bacteria grow and tailor these materials in complex hierarchical structures for specific purposes,
obtaining superior properties compared to man-made cements. Marine animals incorporate
magnesium and macromolecules into their calcium carbonate skeletons to make them stiffer
and increase fracture toughness. A deeper understanding of the processes of the formation,
and the self-assembly of calcium carbonate in aqueous solutions, is the key to understand how
we can target the final material properties of these materials.
In this thesis, atomistic molecular dynamics simulations have been used to study the mechanical properties of magnesian calcites and the interactions between hydrated calcium carbonate
surfaces at nanoconfinement conditions.
The interactions between atomically smooth calcium carbonate surfaces in aqueous solutions
at nanometer scale separations have been computed. The surface forces display characteristic
oscillations due to the structuring of the water confined between the mineral surfaces, at surface
separations < 1.3 nm. Adhesion between the surfaces is observed for surfaces in registry. It is
demonstrated that the adhesion can be reduced or eliminated by shifting the surfaces out of
registry. From the analysis of the surface forces, we derive the interaction potential per unit
area as a function of surface-to-surface separation, which is used to obtain the force between
two spherical calcite colloids via the Derjaguin approximation. We investigate the impact of
surface roughness on the resulting intercolloidal potential. A large enough surface roughness is
shown to eliminate the adhesive properties of calcium carbonate nanoparticles.
The mechanical properties and the deformation response of magnesian calcites was studied
using non-equilibrium molecular dynamics. The energy dissipation mechanisms in magnesian
calcites depends on both the magnesium:calcium composition and the spatial distribution of
these ions is the crystal lattice. By incorporating magnesium into magnesium-rich clusters,
we show that calcium carbonate materials become stiffer than if the magnesium was evenly
distributed.