Anisotropy in Near-Spherical Colloidal Nanoparticles.

Two major aspects of functional colloidal nanoparticles are their colloidal stability (dispersion) and controlled assembly of nanoparticles into ordered structures. Simplifying colloidal nanoparticles as isotropically interacting spheres is unsuitable for small nanoparticles capped with hydrocarbon chain ligands in which the ligand-ligand interaction plays a prominent role in the assembly processes. However, experimentally characterizing the ligand shell structure in solution presents significant challenges, and computer simulations yield divergent results without effective validation. Moreover, the connection between detailed information regarding ligand shell structures and interparticle interactions, in relation to the diverse dynamical behaviors of colloidal nanoparticles, remains poorly understood. In this study, we reveal the relationship between the ligand shell structures, interparticle interactions, and dynamical behaviors of few-nm-sized near-spherical nanoparticles capped with hydrocarbon chain ligands immersed in nonpolar solvents. Our study shows a transformation of the interparticle interactions from anisotropic attractions to isotropic repulsions as a result of the change in the ligand shell structures from order to disorder caused by varying temperature and other factors. The interplay between anisotropic attractions from ligand bundles and isotropic repulsions from disordered ligands dictates the nanoparticle dynamical behaviors of dispersion, uncontrolled aggregation, and controlled assembly.