A molecular dynamics simulation of a 0.1 M ethanol-water solution with
an air/solution interface was performed. Redistribution of ethanol mo
lecules 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 e
thanol excess from neutron reflectivity experiments. A depletion layer
beneath the ethanol surface excess was revealed by the simulation. Et
hanol 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.