Modulating the Mechanical Properties of Supercrystalline Nanocomposite Materials via Solvent–Ligand Interactions

Supercrystalline nanocomposite materials with micromechanicalproperties approaching those of nacre or similarstructural biomaterials can be produced by self-assembly oforganically modified nanoparticles and further strengthened bycross-linking. The strengthening of these nanocomposites iscontrolled via thermal treatment, which promotes the formation ofcovalent bonds between interdigitated ligands on the nanoparticlesurface. In this work, it is shown how the extent of the mechanicalproperties enhancement can be controlled by the solvent used duringthe self-assembly step. We find that the resulting mechanicalproperties correlate with the Hansen solubility parameters of thesolvents and ligands used for the supercrystal assembly: the hardnessand elastic modulus decrease as the Hansen solubility parameter of the solvent approaches the Hansen solubility parameter ofthe ligands that stabilize the nanoparticles. Moreover, it is shown that self-assembled supercrystals that are subsequentlyuniaxially pressed can deform up to 6 %. The extent of this deformation is also closely related to the solvent used during the selfassemblystep. These results indicate that the conformation and arrangement of the organic ligands on the nanoparticle surfacenot only control the self-assembly itself but also influence the mechanical properties of the resulting supercrystalline material.The Hansen solubility parameters may therefore serve as a tool to predict what solvents and ligands should be used to obtainsupercrystalline materials with good mechanical properties