Probing the Adsorption of Polycyclic Aromatic Compounds onto Water Droplets Using Molecular Dynamics Simulations

Abstract

A series of molecular dynamics (MD) simulations were performed to probe the adsorption behaviors of polycyclic aromatic compounds (PACs) from <i>n</i>-heptane and toluene onto water droplets. In <i>n</i>-heptane, the simulations revealed distinct adsorbed structures of PAC molecules on the water droplets with different sizes. In the system with a small water droplet (radius 1.86 nm), the adsorbed PAC aggregate renders a straight one-dimensional (1D) structure; contrarily, in the presence of a large water droplet (radius 3.10 nm), a bent 1D structure of nonzero curvature is formed. Such size effect is a result from the delicate balance between the deformation energy required for adsorption and the available attractions between the PAC and water molecules. While the adsorbed structures are sensitive to the size of the water droplet at relatively low PAC concentration in <i>n</i>-heptane, the size effect in toluene is only prominent when the concentration of PAC molecules is sufficiently high