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

Abstract

Molecular Dynamics (MD) simulations of surfactant-stabilized calcium carbonate, CaCO 3 , nanoparticles in hydrophobic solvent have been carried out to characterize their response to changes in temperature (T) and pressure (P), and also their interaction with trace water and water droplets. The response to increasing temperature and pressure is sensitive to the type of model surfactant, with the sulfonate-stabilized particle, which is the most spherical, showing a weak temperature-pressure dependence, while the sulfurized alkyl phenol (SAP) and salicylate-stabilized particles distort into a more spherical shape with increasing temperature and pressure. The atom-atom radial distribution functions of the core ions reveal consolidation of the calcium carbonate structure with increasing temperature and pressure.The simulations show that the nanoparticles adsorb onto the surface of water droplets through a water bridge transitional mechanism, in agreement with evidence from experimental studies. In the case of the sulfonate surfactant particle, only, a number of surfactant molecules detached from the calcium carbonate core and transferred to the surface of the water droplet. Consequently this type of particle had the greatest interaction with and affinity for water which may explain its rapid neutralization characteristics observed in experiments.The detachment free energy of the sulfonate obtained by potential of mean force (PMF) calculations was the largest of the three, which is consistent with the core being more embedded in the water and less well stabilised on returning to the hydrophobic medium. The salicylate nanoparticle had about half the detachment free energy, which could give rise to a more dynamic equilibrium of attached-to-detached states for this class of nanoparticle.

Mixed Flow Reactor Experiments and Modeling of Sulfuric Acid Neutralization in Lube Oil for Large Two-Stroke Diesel Engines

“…The first step is to investigate the relative resistance with respect to diffusion and adsorption based on Eq. (14).…”

Molecular Dynamics Studies of Overbased Detergents on a Water Surface

“…In the third stage, steered MD and umbrella sampling was used to calculate the free energy of association between two nanoparticles of the same surfactant type, using the same number of species in the OB particle and water as in simulations D to F. The number of each species in the simulations is given in Table . The model nanoparticles in the simulations were performed using the Coulombic annealing and re-forming procedure invented and described in refs − .…”

“…Resolution of this issue reduces to identifying the role that the water interface plays in determining the OB particle shape and also on the effective interaction energy as a function of separation between two OB particles. Our more recent molecular simulation studies have shown that even trace amounts of water interact strongly with the OB calcium carbonate core in the bulk oil. , Therefore, it might reasonably be expected that the effects of surrounding water in the LT experiment arrangement could be significant, although this issue has yet to be fully resolved. This is one of the objectives of this study.…”

“…Our more recent molecular simulation studies have shown that even trace amounts of water interact strongly with the OB calcium carbonate core in the bulk oil. 18,19 Therefore, it might reasonably be expected that the effects of surrounding water in the LT experiment arrangement could be significant, although this issue has yet to be fully resolved. This is one of the objectives of this study.…”

“…There is a body of evidence to support the nanoparticle nature of the overbased chemical additive, in which the individual particles are in the form of reverse micelles each just a few nanometers across. This comes from neutron scattering, − transmission electron microscopy (TEM), − molecular simulation, − and Langmuir trough measurements. ,, The nanoparticle composition of the product facilitates its uniform distribution on dissolution in the oil. The rate of acid neutralization can as a result be controlled more systematically by adjusting the chemistry.…”