The different availability of hydrophobic area at the different MUS:OT ratios determines the aggregate growth, as exemplified in Figure and. For all-MUS NPs, the reduction of the hydrophobic SASA upon dimerization (almost 32%) is such that it becomes almost impossible to establish more hydrophobic bonds, and the growth stops (Figure ). On the contrary, the growth can proceed for MUS:OT 2:1 and 1:1, as shown in Figure . The equatorial region of a dimer, around the NP-NP interface, has the highest MUS (and thus charge) density. Therefore, a third NP will attach more easily at the poles, where the ligands have more conformational freedom than in the equatorial region. Once the linear triplet is formed, the central NP has two neighbors. In the MUS:OT 2:1 case, two is already the maximum possible number of neighbors, and the aggregate can only grow as a linear chain (Figure and S4). In the MUS:OT 1:1 case, the ligand density at the surface of the linear triplets is not yet large enough to prevent further hydrophobic bonds, and 2D growth is possible until the NPs achieve their maximum number of possible hydrophobic bonds, namely four. The aggregates do not develop as isotropic planar lattices since they are more likely to grow from the NPs with the lowest coordination, thus forming ribbons.