Molecular dynamics simulation study of self-assembled monolayers of alkanethiol surfactants on spherical gold nanoparticles

Atomistic molecular dynamics (MD) simulations of self-assembled alkanethiol monolayers are performed to investigate the ligand shell organization of homoligand surfactants on spherical gold nanoparticle surfaces as a function of temperature, nanoparticle size, and ligand tail length. At high temperature, we show that the ligands orient randomly with respect to the surface normal with a small tilt angle. As the temperature decreases, the molecules order and adopt a larger tilt angle. The effects of alkanethiol tail length and nanoparticle size on the tilt structure are also significant. At low temperature, we find the equilibrium conformation of alkanethiols obeys the crystallographic model, whereas at high temperature the continuous model is valid. The dependence of tilt angle on different parameters and comparison with self-assembled monolayers on flat surfaces are also discussed.