Competition of Shape and Interaction Patchiness for Self-Assembling Nanoplates

Progress in nanocrystal synthesis and self-assembly enables the formation of highly ordered superlattices. Recent studies focus on spherical particles with tunable attraction and polyhedral particles with anisotropic shape and excluded volume repulsion, but the interplay between shape and particle interaction is only starting to be exploited. Here we present a joint experimental-computational, multi-scale investigation of a class of highly faceted planar lanthanide fluoride (LnF3) nanocrystals (nanoplates, nanoplatelets). The nanoplates self-assemble in a hexane wetting layer at the liquid-air interface into long-range ordered tilings. Using Monte Carlo simulation, we demonstrate that the nanoplate assembly can be understood from maximization of packing density only in first approximation. Explaining the full phase behavior requires an interaction specificity of nanoplate edges, which originates from the atomic structure as confirmed by density functional theory calculations. Despite the apparent simplicity in particle geometry, the combination of shape-induced entropic and edge-specific energetic effects directs the formation and stabilization of unconventional long-range ordered assemblies not attainable otherwise.

Reference: Nature Chemistry, in press, doi: 10.1038/nchem.1651 (2013)