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 (NPNAT) 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.

No abstract

No abstract

No abstract

We use Monte Carlo computer simulations to investigate tubular membrane structures with and without semiflexible polymers confined inside. At small values of membrane bending rigidity, empty fluid and non-fluid membrane tubes exhibit markedly different behavior, with fluid membranes adopting irregular, highly fluctuating shapes and non-fluid membranes maintaining extended tube-like structures. Fluid membranes, unlike non-fluid membranes, exhibit a local maximum in specific heat as their bending rigidity increases. The peak is coincident with a transition to extended tube-like structures. We further find that confining a semiflexible polymer within a fluid membrane tube reduces the specific heat of the membrane, which is a consequence of suppressed membrane shape fluctuations. Polymers with a sufficiently large persistence length can significantly deform the membrane tube, with long polymers leading to localized bulges in the membrane that accommodate regions in which the polymer forms loops. Analytical calculations of the energies of idealized polymer-membrane configurations provide additional insight into the formation of polymer-induced membrane deformations.