Multiscale Modeling and Simulation of Water and Methane Hydrate Crystal Interface
S Mirzaeifard and P Servio and AD Rey, CRYSTAL GROWTH & DESIGN, 19, 5142-5151 (2019).
Water-methane hydrate interfaces are ubiquitous in oil and gas technologies and in Nature. The structure and properties of this liquid/crystal interface plays a significant role in transport phenomena between the bulk phases. In this paper, we use molecular dynamics techniques to characterize the liquid water-crystalline methane hydrate in the bulk and, particularly, the interface. We show that the interfacial mechanical approach based on the novel constant normal pressure-cross-sectional area (NP(N)AT) ensemble with a computational slab length equal to the lattice parameter of the methane clathrates can accurately predict the interfacial free energy of a curved interface. Notably, the computational platform for the interfacial tension characterization includes contributions from elastic strains. In the studied temperature and pressure ranges, we find that the interfacial tension slightly increases with temperature upturn or pressure drop due to less disordered orientation and dispersed distribution of the molecules at the interface. We generate a full molecular-level characterization by computing the excess enthalpy and stress, local density profile, radial distribution function, hydrogen bonding density, and charge distribution to confirm the observed interfacial tension trend, which significantly contributes to the evolving understanding of gas hydrate formation.
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