SOLUTE ORIENTATIONAL DYNAMICS AND SURFACE-ROUGHNESS OF WATER HYDROCARBON INTERFACES

Molecular dynamics simulations of two model water/alkane interfaces ar e used to sort out the effect of molecular shape on the structure and dynamics of the neat interfaces and the orientational dynamics of a so lute adsorbed at the interface. The two liquid/liquid interfaces are t he water/nonane interface and the one between water and a single atom representation of the nonane molecule whose potential energy function is selected to give properties close to that of nonane. We find that a lthough the thermodynamic properties and relevant structural propertie s of the two interfaces are very similar, the reorientation dynamics o f the solute probe are faster by about a factor of 2 in the water/''sp herical''-nonane system due to different molecular packing and shape.