Abstract Gas hydrates have an important role in environmental and astrochemistry, as well as in energy materials research. Although it is widely accepted that gas accumulation is an important and necessary process during hydrate nucleation, how guest molecules aggregate remains largely unknown. Here, we have performed molecular dynamics simulations to clarify the nucleation path of methane hydrate. We demonstrated that methane gather with a three-body aggregate pattern corresponding to the free energy minimum of three-methane hydrophobic interaction. Methane molecules fluctuate around one methane which later becomes the central gas molecule, and when several methanes move into the region within 0.8 nm of the potential central methane, they act as directional methane molecules. Two neighbor directional methanes and the potential central methane form a three-body aggregate as a regular triangle with a distance of ~6.7 Å which is well within the range of typical methane-methane distances in hydrates or in solution. We further showed that hydrate nucleation and growth is inextricably linked to three-body aggregates. By forming one, two, and three three-body aggregates, the possibility of hydrate nucleation at the aggregate increases from 3/6, 5/6 to 6/6. The results show three-body aggregation of guest molecules is a key step in gas hydrate formation. 

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Three-body aggregation of guest molecules as a key step in methane hydrate nucleation and growth

The use of micro-nano bubbles in groundwater remediation: A comprehensive review

Studies revealed that gas hydrate cages, especially small cages, are incompletely filled with guest gas molecules, primarily associated with pressure and gas composition. The ratio of hydrate cages occupied by guest molecules, defined as cage occupancy, is a critical parameter to estimate the resource amount of a natural gas hydrate reservoir and evaluate the storage capacity of methane or hydrogen hydrate as an energy storage medium and carbon dioxide hydrate as a carbon sequestration matrix. As the result, methods have been developed to investigate the cage occupancy of gas hydrate. In this review, several instrument methods widely applied for gas hydrate analysis are introduced, including Raman, NMR, XRD, neutron diffraction, and the approaches to estimate cage occupancy are summarized.

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Instrumental Methods for Cage Occupancy Estimation of Gas Hydrate

The air micro- and nanobubbles on a silicon wafer surface, generated by ethanol–water exchange method in THF solution, are found with anomalous small contact angles on the gas side due to the pinni...

Effect of Micro- and Nanobubbles on the Crystallizationof THF Hydrate Based on theObservation by Atomic Force Microscopy

With a thorough review on the fundamental relationships between surfaces and hydrates, guiding principles for anti-hydrate surfaces, either targeting anti-hydrate nucleation, anti-hydrate deposition or low hydrate adhesion are deeply discussed. 

Anti-gas hydrate surfaces: perspectives, progress and prospects

The crystallization process of a droplet of tetrahydrofuran (THF) solution on a silicon wafer is studied based on the in situ observation with a high-resolution atomic force microscope. On the basi...

Study of THF Hydrate Crystallization Based on In Situ Observation with Atomic Force Microscopy

Study on the reaction of methane hydrate with gaseous CO2 by Raman imaging microscopy

Gas hydrate is a nonstoichiometric crystalline material. It is attracting more and more attention not only because natural gas hydrate is a potential energy resource, but also because hydrate-based...

Xin Huang

Papers

Instrumental Methods for Cage Occupancy Estimation of Gas Hydrate

Effect of Micro- and Nanobubbles on the Crystallizationof THF Hydrate Based on theObservation by Atomic Force Microscopy

Study of THF Hydrate Crystallization Based on In Situ Observation with Atomic Force Microscopy

Study on the reaction of methane hydrate with gaseous CO2 by Raman imaging microscopy

Advances in molecular dynamics simulation on heterogeneous nucleation of gas hydrate