Wetting properties of passivated metal nanocrystals at liquid-vapor interfaces: a computer simulation study

Molecular dynamics simulations have been employed to determine the contact angles of alkylthiol passivated gold nanocrystals adsorbed at the air-water interface. Simulations were performed using butane-, dodecane-, and octadecanethiol passivated nanoparticles. We demonstrate how the length of the surfactant chain can profoundly influence the wetting behavior of these nanoparticles. All particles were found to be stable at the air-water interface, possessing large, well-defined contact angles. We find that the shape of the dodecane- and octadecanethiol particles is strongly perturbed by the interface. We also present an analysis of the orientational ordering of water molecules at the dodecane-water interface and around butane- and dodecanethiol passivated nanoparticles. The orientational ordering translates into an electrostatic field around the nanoparticles, the magnitude of which corresponds with that of the water liquid-vapor interface.