Molecular dynamics investigation of an ethanol-water solution

A molecular dynamics simulation of a 0.1 M ethanol-water solution with an air/solution interface was performed. Redistribution of ethanol molecules was observed during the simulation, which was initiated from a bulk solution. The results of the simulation show good agreement with surface tension measurements and the number density profiles of the ethanol excess from neutron reflectivity experiments. A depletion layer beneath the ethanol surface excess was revealed by the simulation. Ethanol molecules are oriented at the surface such that the alkyl group points out of the solution. The number of water molecules involved in the hydrogen bonding with the ethanol molecules decreases by a factor of 2 between the surface and the bulk.