Comparison of the binding of polyvinylpyrrolidone and polyethylene oxide to Ag surfaces: Elements of a successful structure-directing agent

We investigate the origins of experimentally observed differences in the structure-directing capabilities of polyvinylpyrrolidone (PVP) and polyethylene oxide (PEO) for the shape-selective, colloidal synthesis of {100}-faceted Ag nanostructures. Using dispersion-corrected density-functional theory, we calculate the binding energies of polymer repeat units to Ag(100) and Ag(111). At the level of the repeat unit, the energetic preference for PEO to bind to {100} facets (∼40 meV) is half that of PVP. At the chain level, we use the Kuhn length to define the polymer binding unit and this is 9 (3) repeat units for PVP (PEO). A thermodynamic model predicts that the {100} binding selectivity of PVP is 10⁷ times higher than that of PEO at synthesis temperatures. These results are consistent with experiment and demonstrate that a distinguishing characteristic of a successful polymer structure-directing agent is the pairing of facet-selective binding of the repeat unit with a sufficiently stiff chain.