Molecular dynamics simulations of the aggregation of nanocolloidal amorphous silica monomers and dimers

Explicit molecular dynamics simulations were applied to an amorphous silica nanoparticle dimer and monomer pair where all original particle diameters were 2.0 nm. Mean forces acting between the silica nanoparticle dimer and monomer were extracted at two different industrially relevant silicon to sodium ratios, where dependences of the aggregates on the potential of mean force on the separation and the silicon to sodium ratio are demonstrated. The pH was indirectly accounted for via the ratio of silicon to sodium used in the simulations. The nature of the interaction of the counter-ions with variation of the numbers of charged silica surface sites (deprotonated silanols) was also investigated. Numbers of bridging hydrogen bonds were found to be strongly dependent on the Si:Na+ ratios. Further to this evidence is found that differing numbers of bridging hydrogen bonds lead to differing aggregation behaviors of silica dimer-monomer nanoparticles.