β-Diketones at Water/Supercritical CO2 Interface: A Molecular Dynamics Simulation

The structural and dynamical properties of hexafluoroacetylacetone (HFA) and acetylacetone (AA) at the water/supercritical CO2 (Sc-CO2) interface at 20 MPa and 318.15 K are investigated by molecular dynamics simulations. The TIP3P potential is used for water and the EPM2 model is for CO2. The water phase and SC-CO2 phase form a distinct immiscible liquid-liquid interface. The two chelating molecules show interfacial preference. Comparatively, the AA molecules show somewhat more preference for interfacial region, whereas the HFA molecules are preferably near the Sc-CO2 phase. The orientational distribution of the β-diketone molecules and the radial distribution functions between β-diketones and solvents are obtained in order to study the microscopic structural properties of the β-diketones at the water-SC-CO2 interface. It is found that the translational diffusion and rotational diffusion of HFA and AA are obviously anisotropic and decrease as the β-diketone molecules approach the interface. The anisotropic dynamic behavior for the solute molecules is related to the corresponding structural properties.