Structural stability evolutions of CH4 and CO2 hydrate-sand nanoparticle systems

Abstract

Despite solid hydrate and mineral particle substances appear extensively in the Earth’s natural environments and engineering applications, physical interactions between hydrates and minerals remain mysterious at the atomic scale due to the experimental challenges at high pressure and low temperature. Herein, particle physical interactions between hydrates and sands are reported using large-scale classical molecular dynamics simulations. Simulation results show that potential energies of nonbonded interactions between different counterparts in hydrate-sand nanoparticle systems exhibit distinctive behaviors, indicative of complex intrinsic interactions among them. Interestingly, both methane and carbon dioxide hydrate nanoparticles are characterized by a thin water layer structure on their surfaces. Molecular structural evolutions of both hydrate and sand nanoparticles are demonstrated in a combination of translational and rotational motions, resulting from van der Waals and Coulombic electrostatic interactions. Moreover, the rotational motion of nanoparticles also depends on thermal fluctuations. Furthermore, hydrate and sand nanoparticles are finally assembled together, accompanied by sintering processes of gas hydrates on sand nanoparticles in good agreement with previous experimental findings. This work quantitatively highlights particle physical interactions between hydrates and sands at the atomic scale, which is of critical importance to understand internal structural evolutions and mechanical stability of gas hydrate systems.