(437b) Adsorption of Carboxylate On Calcite (101 ̅4) Surface: Molecular Dynamics Simulation Approach

Adsorption of Carboxylate on Calcite
() 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.