M. Tarek et al., MOLECULAR-DYNAMICS INVESTIGATION OF THE SURFACE BULK EQUILIBRIUM IN AN ETHANOL-WATER SOLUTION/, Journal of the Chemical Society. Faraday transactions, 92(4), 1996, pp. 559-563
Citations number
20
Categorie Soggetti
Chemistry Physical","Physics, Atomic, Molecular & Chemical
Molecular dynamics simulations of the vapour/solution interface, initi
ated from an ethanol-water mixture at a mole fraction of ethanol, X(e)
= 0.1, have been performed. Rapid redistribution of ethanol molecules
to the free surface was observed during simulations of two different
sized systems. Inspection of the calculated surface structure reveals
that after redistributing the ethanol molecules are preferentially ori
ented such that the alkyl group points out of the solution. A 'depleti
on layer' of enhanced water density beneath the ethanol surface excess
was revealed by the simulation. Analysis of the structure involving m
olecules dose to the surface shows that water molecules are arranged t
o maximize the hydrogen bonding between the oriented ethanol and the a
djacent water molecules. The enhanced water density beneath the interf
ace results from this optimization. The surface tension calculated fro
m the simulation is ca. 50% higher than the results of macroscopic exp
erimental measurements. This overestimation is attributed to shortcomi
ngs in both the potential function and the simulation methodology. The
number density profiles of the ethanol surface excess were compared w
ith results from neutron reflectivity measurements. The calculated pro
files agree better with the experimental measurements at the calculate
d surface tension (i.e. X(e) = 0.022) than those reported for X(e) = 0
.1 mixtures.