Hydrophilic Silica Nanoparticles in O/W Emulsion: Insights from Molecular Dynamics Simulation

Previous studies have been carried out on the effect of silica nanoparticles (SNPs) on the stability of oil-water emulsions. However, the combining configuration of SNPs and oil droplets at the molecular level and the effect of SNP content on the coalescence behavior of oil droplets cannot be obtained through experiments. In this paper, molecular dynamics (MD) simulation was performed to investigate the adsorption configuration of hydrophilic SNPs in an O/W emulsion system, and the effect of adsorption of SNPs on coalescence of oil droplets. The simulation results showed: (i) SNPs adsorbed on the surface of oil droplets, and excessive SNPs self-aggregated and connected by hydrogen bonds. (ii) Partially hydrophilic asphaltene and resin molecules formed adsorption configurations with SNPs, which changed the distribution of oil droplet components. Furthermore, compared with hydrophobic asphaltene, the hydrophilic asphaltene was easier to combine with SNPs. (iii) SNPs would extend the oil droplet coalescence time, and the pi-pi stacking structures were formed between asphaltene and asphaltene or resin molecules to enhance the connection between oil droplets during the oil droplet contact process. (iv) Enough SNPs tightly wrapped around the oil droplet, similar to the formation of a rigid film on the surface of an oil droplet, which hindered the contact and coalescence of components between oil droplets.

Automated summary

In this paper, molecular dynamics (MD) simulation was used to investigate the adsorption configuration of hydrophilic silica nanoparticles (SNPs) in an oil-water emulsion system and their effect on the coalescence of oil droplets. The simulation results showed that SNPs adsorbed on the surface of oil droplets and self-aggregated through hydrogen bonds. Additionally, hydrophilic asphaltene and resin molecules formed adsorption configurations with SNPs, changing the distribution of oil droplet components. SNPs extended the coalescence time of oil droplets and formed pi-pi stacking structures to enhance the connection between oil droplets. Furthermore, a sufficient amount of SNPs tightly wrapped around the oil droplet, hindering the contact and coalescence of components between oil droplets.