⟨ F ⟩=-d pmf (r ) dr (Equation ) The dimer formation is thermodynamically favorable for both hydrophobic and hydrophilic particles in both C4 and C8 ILs with the pmf global minimum at 4.46 nm, which corresponds to the sum of NPs radius. The Δ ag G is more negative for the hydrophilic than for the hydrophobic NPs studied here, and while there is an increase of 90 kJ/mol in the Δ ag G of hydrophobic NPs by increasing the size of the aliphatic chain of the IL cation, the Δ ag G of the hydrophilic NPs is almost unaffected by the solvent replacement. It is important to notice that the stronger thermodynamic tendency of aggregation of the hydrophilic NPs in those ILs does not imply a weak interaction with the solvent. In fact, the hydrophilic NP presents more negative interaction energy with the ILs (Table ), especially due to the strong interaction with the anion.