Molecular modelling studies of calcium carbonate and its nanoparticles

Abstract

Molecular dynamics (MD), simulations have been carried out of crystalline aragonite and calcite, and of finely dispersed calcium carbonate in the form of nanosized inorganic core-organic shell particles. The latter, called overbased detergents commercially, are used as acid-consuming components in automotive and marine engine oils. We have modelled several types of these particles using different surfactant types. We compare the internal structure of the calcium carbonate in these particles with calcite and aragonite crystalline forms using MD in each case. The atomic force-field adopted accounts reasonably well for the crystalline phases, although under unconstrained (constant stress) conditions some distortion of the aragonite structure was noticed. The microstructure of the nanoparticles appears to be quite different to the crystals, and seemingly amorphous. For these small clusters it appears that there is probably no thermodynamic benefit in forming local crystalline order in the cores. The relatively large surface to volume ratio found in these particles lends itself to a more amorphous microstructure.

Response of Calcium Carbonate Nanoparticles in Hydrophobic Solvent to Pressure, Temperature, and Water

“…Bearchell et al 43 are also given in Table 2. The two sets of bulk RDF data are statistically the same.…”

Atomistic theory and simulation of the morphology and structure of ionic nanoparticles

“…To the best of our knowledge, the first published simulations of what might be considered calcium carbonate nanoparticles are due to Bearchell and Heyes. 201 They simulated clusters with ten formula units of CaCO 3 in the presence of surfactant molecules to provide insights relevant to the lubricant industry. Initial particle structures were cleaved from bulk calcite with an approximately spherical morphology.…”

“…Consequently there is a valuable role for atomistic simulation to play in probing nanostructured calcium carbonate. Although bulk phases of calcium carbonate are readily amenable to first principles quantum mechanics, the study of nanoparticles and solution growth is currently largely the realm of force field methods due to the demands of the time-and length-scale required.To the best of our knowledge, the first published simulations of what might be considered calcium carbonate nanoparticles are due to Bearchell and Heyes 201. They simulated clusters with ten formula units of CaCO 3 in the presence of surfactant molecules to provide insights relevant to the lubricant industry.…”

The challenge of biominerals to simulations

“…However some work on surfactants, particularly work on detergent particles, is relevant here. Tobias and Klein, 86 and later Beardsell and coworkers, 87,88 have discussed the structures that consist of calcite nanoparticles (either crystals or amorphous) surrounded by organic surfactant molecules. Including water in the simulation is essential if the correct structure of the surfactant sheath is to be obtained.…”