Although it is well known that solid particles adsorb at interfaces, no consensus has been reached on whether or not the adsorbed nanoparticles affect interfacial tension. In this work the Wilhelmy plate method is implemented in mesoscale dissipative particle dynamics (DPD) simulations to study the influence of nanoparticles on the water-oil interfacial tension. The results are compared with predictions that neglect nanoparticlenanoparticle interactions at the interface. We find that the two estimates can differ significantly. In the regime where nanoparticle-nanoparticle repulsion is large, the Wilhelmy plate method suggests interfacial tension reduction, which appears to be a strong function of nanoparticle surface coverage. Some experimental data from the literature, in apparent disagreement, are re-interpreted based on this insight.

The properties of 3 nm-diameter silica nanoparticles with different surface chemistry were systematically investigated at the decane-water interface using molecular dynamics simulations. Our results show that the decane-water interfacial tension is not much influenced by the presence of the nanoparticles. The three-phase contact angle increases with nanoparticle surface hydrophobicity. Contact angles observed for the nanoparticles at 300 and at 350 K differ very little. The contact angle of the nanoparticle with randomly dispersed hydrophobic groups is smaller than that observed in Janus nanoparticles of equal overall surface chemistry composition. The energy necessary to desorb Janus nanoparticles from the interface is usually higher than that required to desorb the corresponding homogeneous nanoparticles. Desorption from the interface into the aqueous phase is preferred over that into the organic phase for all except one of the nanoparticles considered. Structural and dynamic properties including nanoparticle rotational relaxation, solvent density profiles, and solvent residence autocorrelation functions near the nanoparticles are also presented. The data are useful for designing Pickering emulsions.

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