Surface Chemistry Directs the Tunable Assembly of TiO2 Anatase Nanocubes into Three-Dimensional Mesocrystals

An important step in nanocrystal self-assembly is programming the large-area organization of nanocrystals into superlattices with tunable packing efficiencies. Here we utilize nanoscale surface chemistry to direct the self-assembly of TiO2 (anatase) nanocubes into distinct three-dimensional mesocrystals. High nanocrystal solubility combined with weak electrostatic attraction induced by the pH mediated surface charge was sufficient to organize 3,4-dihydroxyhydrocinnamic acid (DHCA) functionalized nanocubes into large superstructures with both translational and orientational order. The finding that translational and orientational order of nanocrystal superlattices can be induced by the interplay of thermal energy, steric repulsion, and ionic interactions in a nucleation and growth self-assembly process offers insight into the importance of the initial nucleation stage in the self-assembly process and suggests new routes for controlled self-assembly of nanocrystals.