Analysis of Mixed Formic and Acetic Acid Aggregates Interacting With Water: A Molecular Dynamics Simulation Study

Abstract

Water adsorption on aggregates made of equimolar mixtures of formic and acetic acid molecules has been studied by means of molecular dynamics simulations between 150 and 275 K, covering thus a large range of atmospheric temperatures, as a function of both the water content and temperature. Calculations have shown that both the temperature and the water content have a strong influence on the behavior of the corresponding system. Two opposite situations have been evidenced for the acid–water aggregates at sufficiently high water content, namely, water adsorption on large acid grains at low temperatures, and formation of a water droplet with an acid coating at high temperatures. In this latter case, acetic acid molecules have been found at the surface of the water droplet with their hydrophobic methyl group being as far as possible from the water surface, whereas part of the formic acid molecules were in the inner side of this interface. At low water content and high temperatures, this acid–water mixing was ...