266469 Adsorption of Carboxylate On Calcite (101 ̅4) Surface: Molecular Dynamics Simulation Approach
Byeong Jae Chun, Seung Geol Lee, Giuseppe F. Brunello, Ji Il Choi and Seung Soon Jang
Computational NanoBio Technology Laboratory, School of Materials Science and Engineering, Georgia Institute of Technology, 771 Ferst Drive NW, Atlanta, GA 30332-0245
To study the wettability alteration of calcite surface in oil reservoir, we investigate the molecular adsorption of carboxylate on the calcite surface using full-atomistic molecular dynamics (MD) simulation as well as density functional theory (DFT). First, we investigate the most probable binding site on the calcite for the chemisorption of carboxylate using DFT calculations in DMol3. Once finding the binding site, we obtain the molecular interaction energy curve as a function of distance in which the dispersion interaction is calculated using DFT-D3. In order to take into account the molecular interaction between various molecules including oil, water and surfactant in our MD simulations, we determine a force field, especially off-diagonal van der Waals interactions: 1) Morse potential functions are fitted to reproduce the chemisorption binding energy obtained from the previous DFT calculation; 2) Morse potential function is also used to describe the non-chemisorption interactions between molecules and calcite surface; 3) Lennard-Jones potential functions are used to describe the interaction between the different types of molecules (e.g., oil-water pair); 4) Regarding van der Waals interactions between the same type of molecules such as calcite-calcite, oil-oil and water-water pairs, we employ the given original force fields. After developing the Force Field, we perform MD simulations to obtain the equilibrium structures and evaluate the thermodynamic stability of the chemisorbed carboxylate on calcite in comparison to that of the carboxylate in molecular assembly with surfactants. Through this study, we aim at characterizing the molecular mechanisms of the surfactant-driven carboxylate desorption.