Nanoparticle Superlattices with Polymer Ligands*

We provide a study of the assembly of single component nanocrystals (nanoparticles) NCs capped with polystyrene by solvent evaporation. We investigate regimes from the colloidal R_G/R_C<<1 with R__C (core radius) and R_G (ligand gyration radius) to the polymer limit R_G/R_C>>1. We show that for increasing chain length, there is the emergence of a ``cascade effect'', i.e. an abrupt drop in internal energy with the resulting potential of mean force dominated by configurations wherein the chains bend over the core in order to maximize contacts with the other NC, which accounts for the large magnitude of the many body effects in the superlattice free energy. Interestingly, the Orbifold Topolgical Model (OTM) that successfully characterizes the nanocrystal interaction in the colloidal limit, quantitatively describes the polymer limit as well. Our results establish that bcc is the equilibrium phase. Implications for recent and future experiments are discussed.