Structure and dynamics of mixed dipolar liquids near solid surfaces: a molecular dynamics simulation study

The structural and dynamical properties of binary Stockmayer liquids near solid surfaces are investigated by means of molecular dynamics simulations. The two solvent components differ widely in their polarity and they are mixed at varying mole fraction. The dipolar mixtures are confined between two planar solid surfaces and the properties of the interfacial molecules are calculated in terms of several equilibrium and time dependent quantities such as the number density, orientational structure, perpendicular (z) and parallel (x,y) components of translational diffusion tensors, rotational diffusion coefficients and various time correlation functions of both the species. The extent of selective adsorption of one species against the other at the surface is investigated and its effects on various dynamical properties of the interfaces are discussed. The dynamics of solvation of a newly created charge distribution near a solid surface is also studied and the results are compared with the dynamics of solvation in mixed solvent in the bulk phase. The solvation at the interface is found to occur at a much slower rate primarily because of the selective adsorption of the less polar solvent at the solid surface and redistribution of solvent molecules near the solute.