The C4 solvent around both NPs displays only a short-range ordering, as can be seen by the g(r) achieving the ideal value of 1 just after two solvation layers (considering here one layer due to the hydrophobic and another due to the hydrophilic portion of the IL). The solvent structure becomes more interesting in the C8 solvent (Figure ). First, the longer alkyl group makes the first layer more structured even for the hydrophilic NP, which results in the increase of hydrophilic NP-anion interaction energy in C8 in comparison with C4 (Table ). Also, the longer alkyl group leads to domain segregation between the polar and apolar portions of the ionic liquid (Figure ). center as can be seen by the radial distribution functions in Figure . Those alternated layers around NPs result in the complex long-range behavior of the pmfs in the C8 IL: As the two NPs approach, there is a superposition of the solvent layers around them. Depending on the distance between the particles, there may be a superposition between hydrophobic and hydrophilic layers, resulting in a solvent-mediated repulsion that results in the local maxima of the pmfs, or there may be a superposition of same type layers resulting in the local minima of the pmfs (solid curves in Figure ). This can be seen by the graphical representation of selected structures along the pmf calculations in C8 (Figure ), where we can notice some mixture of polar and apolar sites of the IL between NPs in the position of the first maximum and the formation of more well defined polar and apolar layers between them when the distance corresponds to the minima of the pmf. The distance between layers of opposing natures in the g(r) curves of Figure stands for ca. 2.1 nm, thus, if at a given distance between NPs there is a superposition of layers of the same kind, moving one particle 2.1 nm either closer or farther to the other lead to an unfavorable superposition of hydrophilic and hydrophobic layers, which results in the separation of consecutive maxima and minima points of the pmf (Figure ) also being of ca. 2.1 nm. Those distances are the same for both hydrophilic and hydrophobic particles, indicating that the relative positions of the maxima and minima in the pmf are governed by the size of the domains formed in the solvent and do not depend on the nature or strength of the interaction between the NP and the solvent. However, the NP-solvent interaction affects the intensity of the solvent structure around NPs which, in turn, defines the height of the barriers in the pmf. In the models studied here, the hydrophobic NP induces a stronger organization of the C8 IL than the hydrophilic particle and, as a consequence, presents higher barriers for the dimer association in the pmf. nm), at the first barrier top (r = 5.3 nm) and at the second minimum (r = 6.7 nm). Color scheme is the same used in Figures and.