**Computing contact angles for oil-water-rock systems via thermodynamic
integration**

R Patel and RKR Addula and M Shaik and SN Punnathanam, JOURNAL OF CHEMICAL PHYSICS, 157, 134705 (2022).

DOI: 10.1063/5.0101013

Wettability of rock surfaces with respect to oil and water, which is
characterized by the contact angle, is an important factor that
determines the efficacy of enhanced oil recovery operations.
Experimental determination of contact angles for oil-water-rock systems
is expensive and time-consuming due to the extremely long times needed
for the establishment of adsorption equilibrium at the liquid-solid
interface. Hence, molecular simulations form an attractive tool for
computing contact angles. In this work, we use the cleaving wall
technique that was developed previously in our group **R. K. R. Addula
and S. N. Punnathanam, J. Chem. Phys. 153, 154504 (2020)** to compute
solid-liquid interfacial free energy, which is then combined with
Young's equation to compute the oil-water contact angle on silica
surfaces. The silica surface is modeled with the INTERFACE force field
that has been developed to accurately reproduce experimental data. We
have considered three different surface chemistries of silica, namely,
Q(2), Q(3), and Q(4), in this study. Our calculations reveal that while
the Q(2) and Q(3) surfaces are completely wetted by water, the Q(4)
surface is partially non-wetted by water. All the simulations needed for
this calculation can be performed using the Large-scale Atomic/Molecular
Massively Parallel Simulator (LAMMPS) molecular package. This should
facilitate wider adoption of the Young's equation route to compute
contact angles for systems comprised of complex molecules. Published
under an exclusive license by AIP Publishing.

Return to Publications page