Molecular dynamics simulation of nanocolloidal amorphous silica particles: Part I

Abstract

Explicit molecular dynamics simulations were applied to a pair of amorphous silica nanoparticles in aqueous solution, with diameter of 4.4 nm and with four different background electrolyte concentrations, to extract the mean force acting between the two silica nanoparticles. Dependences of the interparticle forces on the separation and the background electrolyte concentration were demonstrated. The nature of the interaction of the counterions with charged silica surface sites (deprotonated silanols) was investigated. A "patchy" double layer of adsorbed sodium counterions was observed. Dependences of the interparticle potential of mean force on the separation and the background electrolyte concentration were demonstrated. Direct evidence of the solvation forces is presented in terms of changes of the water ordering at the surfaces of the isolated and double nanoparticles. The nature of the interaction of the counterions with charged silica surface sites (deprotonated silanols) was investigated in terms of quantifying the effects of the number of water molecules separately inside each pair of nanoparticles by defining an impermeability measure. A direct correlation was found between the impermeability (related to the silica surface "hairiness") and the disruption of water ordering. Differences in the impermeability between the two nanoparticles are attributed to differences in the calculated electric dipole moment.

Implicit solvent model for effective molecular dynamics simulations of systems composed of colloid nanoparticles and carbon nanotubes

“…Recent large-scale molecular dynamics simulations have brought some clues for understanding the forces acting between two nanometer-sized spheroids in solution [22,23]. An important conclusion drawn from those calculations is that Hamaker theory [24,25] is fairly well obeyed even for nanoparticles with diameters ca.…”

Forces between functionalized silica nanoparticles in solution

“…Numerical simulations of discrete solvent effects on nanoparticles have been impractical until now because of the large systems required to avoid significant finite-size effects due to the long-range hydrodynamic interactions. For single-particle diffusion, these corrections have been shown [5,6] to scale as R/L where R is the particle radius and L is the simulation cell length.Recent studies have computed the potential of mean force for bare silica nanoparticles in an aqueous medium, with and without electrolytes present [7]. Forces between bare colloidal nanoparticles have also been studied in LennardJones fluids and in n-decane [8].…”

“…Recent studies have computed the potential of mean force for bare silica nanoparticles in an aqueous medium, with and without electrolytes present [7]. Forces between bare colloidal nanoparticles have also been studied in LennardJones fluids and in n-decane [8].…”

Molecular dynamics simulation of nanocolloidal amorphous silica particles: Part II

“…We have performed our simulations for a number of industrially relevant ranges of the silicon to sodium ͑Si: Na + ͒ ratio, which we use to indirectly account for varying pH ͑see Secs. II and III for more details and the companion paper 25 to this current work, where the details of the modeling of amorphous silica particle structure and allocation of surface charge 1 on silica test particles are provided͒.…”