Conformations and Effective Interactions of Polymer-Coated Nanoparticles at Liquid Interfaces

We investigate conformations and effective interactions of polymer-coated nanopar- ticles adsorbed at a model liquid-liquid interface via molecular dynamics simulations. The polymer shells strongly deform at the interface, with the shape governed by a balance between maximising the decrease in interfacial area between the two solvent components, minimising unfavourable contact between polymer and solvent and max- imising the conformational entropy of the polymers. Using potential of mean force calculations we compute the effective interaction between the nanoparticles at the liquid-liquid interface. We find that it differs quantitatively from the bulk and is sig- nificantly affected by the length of the polymer chains and by the solvent quality. Under good solvent conditions the effective interactions are always repulsive and soft for long chains. The repulsion range decreases as the solvent quality decreases. In particular, under poor solvent conditions, short chains may fail to induce steric repul- sion, leading to a net attraction between the nanoparticles, whereas with long enough chains the effective interaction potential may feature an additional repulsive shoulder at intermediate distances.