The influence of surface roughness on the adhesive interactions and phase behavior of suspensions of calcite nanoparticles

We investigate the impact of nanoparticle roughness on the phase behaviour of suspensions in models of calcium carbonate nanoparticles. We use a Derjaguin approach that incorporates roughness effects and interactions between the nanoparticles modelled with a combination of DLVO forces and hydration forces, derived using experimental data and atomistic molecular dynamics simulations, respectively. Roughness effects, such as atomic steps or terraces appearing in mineral surfaces result in very different effective inter-nanoparticle potentials. Using stochastic Langevin Dynamics computer simulations and the effective interparticle interactions we demonstrate that relatively small changes in the roughness of the particles modify significantly the stability of the suspensions. We propose that the sensitivity of the phase behavior to the roughness is connected to the short length scale of the adhesive attraction arising from the ordering of water layers confined between calcite surfaces. Particles with smooth surfaces feature strong adhesive forces, and form gel fractal structures, while small surface roughness, of the order of atomic steps in mineral faces, stabilize the suspension. We believe that our work helps to rationalize the contrasting experimental results that have been obtained recently using nanoparticles or extended surfaces, which provide support for the existence of adhesive or repulsive interactions, respectively. We further use our model to analyze the synergistic effects of roughness, pH and ion concentration on the phase behavior of suspensions, connecting with recent experiments using calcium carbonate nanoparticles

Molecular dynamics simulations of nanostructured tight rocks

A clay nanopore model is developed using well tested force fields for water, carbon dioxide and portlandite. Transport properties of water and carbon dioxide confined witin a portlandite nanopore is adressed, where the diffusion as a function of distance to the nanopore surface is calculated. Binding energies of carbon dioxide to a alpha-quartz surface is calculated, as well as surface energies, using a reactive force field

Hydration interactions under nanoconfinement and bulk deformation of calcium carbonate: insight from molecular dynamics simulations

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.Open Acces