Molecular level investigation on the dispersion of hydrophilic modified SiO₂ nanoparticles in water from a bond energy viewpoint

Abstract

The dispersion characteristic of nanoparticles is of more interest in some engineering applications, including polymer filling, foam stability, chemical catalysis, and materials surface package. In this paper, the surface modification of SiO 2 nanoparticles was carried out based on molecular dynamics simulation. The characteristics of aggregation and diffusion of SiO 2 nanoparticles were explained by the radial distribution function (RDF), concentration profile, length distribution, mean squared displacement (MSD), and microscopic testing (MT). The results showed that the orbital provided by the three types of atoms (H, O, and Si) corresponding to the different bandwidths caused the energy alternation of state density. According to the results of RDF, the H O bond energy mainly provided by the water molecules showed the maximum bond energy with 463 kJ/mol. The results indicated that the bonds breakage and formation were accompanied by changes in total energy, kinetic energy, non-bond energy, and potential energy. After the modification of SiO 2 nanoparticles, the concentration profile of the water molecules decreased first at 1-8.5 Å and then increased at 8.5-17.2 Å, but the length distribution climbed to 15.7 at 0.975 Å.When the temperature reached 398 K, the peak value of the length distribution declined to 13.6 Å and the relative concentration profile of water molecules fluctuated around 1.0. With the increase of salinity, the peak value of length distribution reached 15.7 at 0.975 Å, but the concentration profile of water molecules at 3.1-9 Å decreased quickly and then gradually increased. The results of MSD and MT about water molecules presented the largest diffusion coefficient appeared at 398 K and had the best dispersion effect owing to the average kinetic energy among the molecules. Conversely, the diffusion coefficient decreased with the incremental solution salinity because the inhabitation of sodium for the motion of water molecules resulted in the ion bridging and hydrogen bonding.

Effects of Sulfate Ions on Crude Oil Adsorption/Desorption on Carbonate Rocks: Experimental and Molecular Simulations

“…Currently, the application system of molecular dynamics simulation (MDS) is becoming more and more mature, , which can characterize the interaction forces between different complex systems on a molecular scale, , including electrostatic force, Coulomb force, and van der Waals force, and describe the dynamics, energy, relative concentration, and other characteristics of complex systems in detail . Molecular dynamics can be used to simulate the process of oil film adsorption and desorption on the surface of carbonate rocks and explain the mechanism of wettability change on the surface of carbonate rocks from the perspective of the digital model and the molecular scale.…”