An ongoing challenge in the field of semiconductor nanoparticles (NPs) is to increase their solubility, particularly in apolar solvents, where the colloidal stability of NPs is typically limited, and relevant theoretical treatment is lacking. One common strategy to increase this stability involves modifying the NP-grafted ligands. Contrary to common wisdom, our experiments indicated that the dependence on chain length can be nonmonotonic: short and long chains destabilized CdSe NPs but intermediate-sized ones were stabilizing. In this proposal, we aim to determine the interactions acting between NPs in solution, and to resolve how these vary with ligand type. We propose to use exacting SAXS measurements to extract the second virial coefficient, which combined with all-atom Molecular Dynamics simulations will allow to evaluate the interaction potential between the NPs. Our work should shed light on the unique properties of hydrocarbon ligands and their role in stabilizing NPs.