(510j) Effects of Surface Roughness on Self-Assembly of ?-Phase Sodium Yttrium Fluoride Nanocrystals

Self-assembly of nanoparticles is crucial in constructing the unique physical and chemical properties that are associated with their final assembled configurations. While energetics of self-assembly such as electrostatic and van der Waals interactions is reasonably well understood, the importance of hydrodynamics remains to be fully explored. We use a single-beam optical tweezer that imposes an external attractive force field to investigate the self-assembly of a model system based on the α-phase sodium yttrium fluoride (α-NaYF) nanocrystals. We find that the surface roughness of α-NaYF nanocrystals has a drastic impact on their observed self-assembly behavior, with rough particles assembly more spontaneously than their smooth counterparts. A combination of both hydrodynamic resistivity calculations and Langevin dynamics simulations demonstrates that the hydrodynamic force depends heavily on the surface roughness of the nanocrystals and plays a crucial role in their self-assembly. This work clearly indicates the important role of dynamics in obtaining a mechanistic understanding of self-assembly.