Electrostatic-driven ridge formation on nanoparticles coated with charged end-group ligands

Using coarse-grained molecular dynamics simulations, we investigate the surface patterns of charged end-group ligands attached to faceted nanoparticles. A competition between electrostatic repulsion and hydrophobic ligand-ligand attraction leads to the formation of a number of different conformations of the ligand coatings. The most prominent conformation in icosahedral nanoparticles is a ridgelike structure that makes their surfaces highly anisotropic. Meanwhile, bundles seem more prominent than ridges for tetrahedral, cubic, octahedral, and dodecahedral nanoparticles of diameters comparable to the chain length. The applicability of the Debye-Huckel theory to describe the ridges is confirmed by comparing simulations with explicit ion simulations. We argue that a tunable ligand-coating pattern can be used as a simple and robust tool for achieving direction-dependent interactions between nanoparticles and provide control of their assembly into composite materials with a desired symmetry.