Structure and Dynamics of Aqueous and Aqueous-Hydrocarbon Fluids between Charged Surfaces Yongsheng Leng, Department of Mechanical and Aerospace Engineering, The George Washington University, Washington, DC 20052 Realistic CVFF (consistent valence force field) and atomic charges for aqueous-hydrate-clay systems are used to study the adsorption structure of water and ions near charged clay surfaces. A liquid-vapor canonical-ensemble molecular dynamics (LV-NVT-MD) approach is employed. Simulation results for the density distributions when H3O+ ions exchanging K+ ions are more consistent with X-ray reflectivity experiments. a b Density distributions of water and ions in H3O+ (case a) and K+ (case b) aqueous films. For (a), the locations of the first three peaks of the total O density (approximately equivalent to the measure of total electron density) are very close to those in the X-ray reflectivity experiment. The potassium ions (case b) are more diffused into inner layers, indicating that most potassium ions are fully hydrated, rather than partially hydrated Simulations of methane hydrate between K-Montmorillonite surfaces show that methane tends to migrate to montmorillonite surface to form inner-sphere complex, while potassium ions are fully hydrated to form outer-sphere complex. Density distributions of methane and K+ ions, and methane-hydrate molecular adsorption structure between two single-sheet K-montmorillonite surfaces. Methane molecules are in yellow, and potassium ions are in purple