How Does Cage Occupancy Affect the Mechanical Response of Methane Hydrate under Strain Conditions

QL Bai and DS Bai, JOURNAL OF PHYSICAL CHEMISTRY C, 129, 21098-21111 (2025).

DOI: 10.1021/acs.jpcc.5c05036

As a potential energy source, understanding the fundamental mechanical behavior of methane hydrate is important for its exploitation and transportation. Herein, the mechanical properties and response behavior of methane hydrate with various cage occupancies and temperatures were studied by molecular dynamics simulations. Results indicate that methane in hydrate cages can make the cage stable through van der Waals interactions, causing an increase in both the elastic modulus and the maximum stress. The type of empty cages has vastly different effects at different stages of stretching: under similar cage occupancy conditions, the empty-large-cage hydrate shows a higher elastic modulus in the linear elastic stage, but in the nonlinear and fracture stages, the empty-small-cage hydrate has a significantly higher maximum stress rise. The mechanical properties of the hydrate are mainly determined by the hydrogen bond network. The breaking of hydrogen bonds during the stretching process may be a possible reason for the system deviating from Hooke's law. In the nonlinear deformation stage, the hydrogen bonds usually break near the already broken hydrogen bonds, leading to the fracture of the hydrate ultimately from these locations. Empty cages and large cages with a certain orientation are more prone to deformation. According to energy analysis, to break the same number of hydrogen bonds, the energy required by stretching is only one-third of that by heating, owing to its "dimensional advantage". The mechanical properties of the hydrate changed linearly with temperature. The presence of methane will increase its elastic modulus and maximum stress to the same extent at all temperatures.

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