Simulation of the THF hydrate-water interfacial free energy from computer simulation

TL;DR

This study uses molecular dynamics simulations with Mold Integration to accurately predict the interfacial free energy between THF hydrate and water, aligning well with experimental data and demonstrating the method's effectiveness for complex hydrate interfaces.

Contribution

First computational prediction of THF hydrate-water interfacial free energy using Mold Integration, validating the method for complex hydrate-fluid interfaces.

Findings

Predicted interfacial free energy: 27(2) mJ/m²

Excellent agreement with experimental data: 24(8) mJ/m²

Method applicable to complex hydrate structures

Abstract

In this work, the tetrahydrofuran (THF) hydrate-water interfacial free energy is determined at $500\,\text{bar}$, at one point of the univariant two-phase coexistence line of the THF hydrate, by molecular dynamics simulation. The Mold Integration-Host methodology, an extension of the original Mold Integration technique to deal with hydrate-fluid interfaces, is used to calculate the interfacial energy. Water is described using the well-known TIP4P/Ice model and THF is described using a rigid version of the TraPPE model. We have recently used the combination of these two models to accurately describe the univariant two-phase dissociation line of the THF hydrate, in a wide range of pressures, from computer simulation [J. Chem. Phys. 160, 164718 (2024)]. The THF hydrate-water interfacial free energy predicted in this work is compared with the only experimental data available in the literature. The value obtained, $27(2)\,\text{mJ/m}^{2}$, is in excellent agreement with the experimental data taken from the literature, $24(8)\,\text{mJ/m}^{2}$. To the best of our knowledge, this is the first time that the THF hydrate-water interfacial free energy is predicted from computer simulation. This work confirms that the Mold Integration technique can be used with confidence to predict solid-fluid interfaces of complex structures, including hydrates that exhibit sI and sII crystallographic structures.