How Is the Surface Tension of Various Liquids Distributed along the Interface Normal?

Abstract

The tangential pressure profile has been calculated across the liquid–vapor interface of five molecular liquids, i.e., CCl4, acetone, acetonitrile, methanol, and water, in molecular dynamics simulations using a recently developed method. Because the value of the surface tension is directly related to the integral of this profile, the obtained results can be interpreted in terms of the distribution of the surface tension along the interface normal, both as a function of distance, either from the Gibbs dividing surface or from the capillary wave corrugated real, intrinsic liquid surface, and also in a layerwise manner. The obtained results show that the surface tension is distributed in a 1–2 nm wide range along the interface normal, and at least 85% of its value comes from the first molecular layer of the liquid in every case. The remaining, roughly 10% contribution comes from the second layer, with the exception of methanol, in which the entire surface tension can be accounted for by the first molecular layer. Contributions of the third and subsequent molecular layers are found to be already negligible in every case.