Solvation forces in water nanofilms confined between calcium carbonate surfaces

Calcium carbonates are polymorphic minerals, abundant in the earth’s crust. It is the main building block of shells and bones and other cementing materials such as industrial cement widely used in construction. It is... [ view full abstract ]

Calcium carbonates are polymorphic minerals, abundant in the earth’s crust. It is the main building block of shells and bones and other cementing materials such as industrial cement widely used in construction. It is believed that solvation forces play an important role in the calcium carbonate growth and dissolution process. These solvation forces arise from the structuring of water molecules when they are confined between two surfaces at nanometer separation. The ordering of the molecules is expected to vary with the surface structure and hydrophobic character. A better understanding of solvation forces is essential to develop models of microscopic mechanisms explaining growth and dissolution at the atomic scale, a key to understand biomineralization and to improve the mechanical properties of man-made cementing materials.

We have performed grand canonical molecular dynamics simulations of water nanofilms confined between calcium carbonate polymorphs, calcite and aragonite. The solvation depends strongly on the surface considered, namely the (001) surface of aragonite and the (10.4) surface of calcite, which have orthorhombic and hexagonal symmetry respectively. The surfaces induce very different water adsorption patterns, which leads to very different solvation forces. The latter feature long decay lengths over 3 nm, in pure water, while the decay is much shorter in the case of the aragonite. At short interfacial separations (< 1nm) the surface forces are dominated by the interaction of two strongly adsorbed water layers, and is expected to play a key role in defining the wettability of these surfaces.