(687g) Self-Assembled Monolayer of Carboxylate On Calcite (101 ?4) Surface: Molecular Dynamics Simulation Approach

Chun, B., Georgia Institute of Technology
Lee, S. G., Georgia Institute of Technology
Brunello, G. F., Georgia Institute of Technology
Choi, J. I., Georgia Institute of Technology
Jang, S. S., Georgia Institute of Technology

Self-Assembled Monolayer of
Carboxylate on Calcite

Molecular Dynamics Simulation

Byeong Jae Chun, Seung Geol Lee, Giuseppe F. Brunello, Ji Il Choi and Seung Soon

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).  There are three types of carboxylate adsorbate used for this
study; benzoate, dodecanoate (C12), and octadecanoate (C18). Using DFT
calculation, the molecular details of carboxylates are determined including the
quantum charge and optimal configuration. Once the fundamental information of
the adsorption models is attained, MD simulations are performed to obtain the
equilibrium structures and evaluate the thermodynamic stability of the
chemisorbed carboxylate and their self-assembled monolayer (SAM) on calcite. Our
force field contains the newly developed parameters for the off-diagonal van
der Waals interactions of carboxylate functional group with calcite surface. The
given original force fields are employed for van der Waals interactions between
the same type of atoms or molecules. Based on the thermodynamic stability of
each adsorption case achieved by our MD simulations, we determine the optimal
packing density of carboxylate SAM on the calcite surface for each case and
characterize the corresponding structures. In order to determine the effect of
solvation on the packing and structures of SAM on calcite surface, we simulate
the same systems in the presence of solvent phase such as water and octane. Once
equilibrated structures of carboxylate SAM are obtained, the free energy
barrier for detachment of carboxylate from the surface is evaluated by applying
potential of mean force (PMF) in order to assess the kinetics of wettability
alteration as well as thermodynamic stability.