Ligand Packing Dictates Interparticle “Bonding” in Nanoparticle Self-Assembled Structures

This study examines how the packing of ligand shells in inorganic nanoparticle–organic ligand complexes─either disordered or crystalline─affects the properties of the assembled structures. Using a typical system of 5 nm spherical nanoparticles with a ligand grafting density of 5.5 nm –2, molecular simulations reveal that at room temperature, (Z)-8-hexadecene (HDE) ligands preserve the disordered shell formed at high temperature, while hexadecane (HDA) ligands crystallize into ordered bundles. Nanoparticles with ordered bundles interact through an interlocking mechanism, with the number of interlocked bundles increasing with the nanoparticle coordination number. In contrast to disordered ligands, which contact via cone-shaped defects, ordered ligand systems exhibit stronger interparticle “bonds” and pronounced many-body effects. The elastic modulus of the ordered structures is nearly twice that of their disordered counterparts, underscoring the pivotal role of ligand packing in determining the mechanical properties of nanoparticle assemblies.