Quantifying pressure effects on the THF hydrate–water interfacial free energy at coexistence conditions: A computer simulation study

Abstract

In this study, the tetrahydrofuran (THF) hydrate–aqueous interfacial free energy, γhw, is determined along the univariant two-phase coexistence line of the THF hydrate from molecular dynamic simulations. In particular, we determine γhw at 100, 250, and 1000 bar and at the corresponding coexistence temperatures. γhw is directly evaluated from simulations using the mold integration–host methodology, which is an extension of the original mold integration method. Water and THF molecules are described using the well-known TIP4P/ice model and a rigid version of the TraPPE model, respectively. This study is a natural extension of our previous studies, where the same model combination was used to describe the univariant two-phase dissociation line of the THF hydrate in a wide range of pressures [J. Algaba et al., J. Chem. Phys. 160, 164718 (2024)] and to calculate the THF hydrate–water γhw value at 500 bar and the corresponding coexistence temperature [M. J. Torrejón et al., J. Chem. Phys. 161, 064701 (2024)]. The results obtained in this study show excellent agreement with the only experimental data reported in the literature, 24(8) mJ/m2. This is the first time that the THF hydrate–water γhw is predicted along the univariant two-phase dissociation line of the THF hydrate. Our results suggest that there exists a minimum of energy at intermediate-low pressures and, in general, the γhw does not change significantly with the pressure in the range considered in this study. Once again, it is confirmed that the mold integration–host technique can be used to predict directly and accurately the hydrate–water γhw for hydrates with a sII crystallographic structure.