Studies on interfacial structures of electrolyte solutions are not only of theoretical significance, but also valuable for practical applications. In this work, molecular dynamics simulations were carried out to investigate the interfacial properties of LiCl, LiBr, LiI, NaI, KI, CsI solutions at 1×105 Pa and 300 K, which was aimed to discover the relationship between hydration theory and interfacial structures of electrolyte solutions. The effect of hydration strength of cations on interfacial structures of anions was explored. Simulation results indicate that for those with stronger hydration ability, they tend to stay in the bulk region whereas for ions with weaker hydration ability, they tend to aggregate in the interfacial region. This mechanism provides a reasonable explanation for the distribution behavior of ions at interfaces. The hydration ability of cations is usually stronger than that of anions, so cations tend to stay in the bulk region while counter anions prefer to aggregate in the interfacial region. The interfacial profiles of anions are closely related with their hydration ability, the weaker the hydration ability, the higher the interfacial profiles at interfaces. The tendency of anion aggregation at interfaces is Cl－＜Br－＜I－. The hydration ability of cations also affects the interfacial profiles of co-existing anions, as the hydration ability of cations gets weaker, the interfacial profiles of co-existing anions become lower.

Key words: electrolyte solution, interfacial structure, ionic hydration, molecular simulation, molecular dynamics