Molecular Simulations of Surfaces of Aqueous Solutions

Abstract

This thesis consists of 18 papers, in which we investigated the behavior of molecules and ions at aqueous interfaces by means of molecular dynamics (MD) simulations. We started our simulations with the surface of neat water, where we investigated the behavior of hydronium and hydroxide ions, i.e., the products of autolysis of water that are of 10�7M concentration in pure water. The results, ranging from ab initio high level calculations on water clusters and ab initio dynamics on small systems to statistically converged classical molecular dynamics simulations are mutually consistent47,48,50. The observed surface adsorption of hydronium is also consistent with the surface selective spectroscopy experiments (VSFG, SHG, PES)45,51,55{59, surface tension measurements60, and with _-potential measurements of acidic solutions62,63. The spectroscopy and surface tension experiments are also in agreement with the weak surface repulsion/non-accumulation of hydroxide observed in our simulations. However, there are macroscopic measurements, such as higher pH electrophoretic mobility measurements, titration of oil emulsions, and thin _lm stability experiments that indicate a negative charge on air/water and oil/water interfaces 61{71. Even though these experiments do not directly reveal the chemical nature or...

This thesis consists of 18 papers, in which we investigated the behavior of molecules and ions at aqueous interfaces by means of molecular dynamics (MD) simulations. We started our simulations with the surface of neat water, where we investigated the behavior of hydronium and hydroxide ions, i.e., the products of autolysis of water that are of 10�7M concentration in pure water. The results, ranging from ab initio high level calculations on water clusters and ab initio dynamics on small systems to statistically converged classical molecular dynamics simulations are mutually consistent47,48,50. The observed surface adsorption of hydronium is also consistent with the surface selective spectroscopy experiments (VSFG, SHG, PES)45,51,55{59, surface tension measurements60, and with _-potential measurements of acidic solutions62,63. The spectroscopy and surface tension experiments are also in agreement with the weak surface repulsion/non-accumulation of hydroxide observed in our simulations. However, there are macroscopic measurements, such as higher pH electrophoretic mobility measurements, titration of oil emulsions, and thin _lm stability experiments that indicate a negative charge on air/water and oil/water interfaces 61{71. Even though these experiments do not directly reveal the chemical nature or...