Mechanical stability of fluorinated-methane clathrate hydrates

Abstract

• Lattice constant of clathrate hydrates formed by encapsulating fluorinated methane derivatives is greatly dictated by the number of fluorine atoms. • Polar fluorinated methane derivatives@cage show distinct rotational dynamics that vary with global strain. • Mechanical properties of clathrate hydrates are greatly influenced by the size and dipole moment of guests. • Unconventional water cages form as clathrate hydrates are mechanically failed via fractures of water cages. Clathrate hydrates recently find important practical applications in the capture and recovery of greenhouse gases, cold storage and refrigeration systems. Nevertheless, their properties at microscopic scale remains largely insufficient yet. Herein, the structure and stability of clathrate hydrates encapsulating fluorinated methane derivatives under mechanical load are investigated by molecular dynamics simulations. All investigated clathrate hydrates are structurally stable host-guest molecular crystals yet show distinct structural and mechanical behaviors. Lattice constant of those clathrate hydrates is dictated by the size and dipole moment of fluorinated methane, for example, it is initially enlarged with increasing fluorine atom in the methane guest molecule but followed by reduction as the guest molecule becomes tetrafluoromethane. However, clathrate hydrates encapsulating non-polar fluorinated methane show superior mechanical properties over those encapsulating polar ones. Polar fluorinated methane derivatives@clathrate cages exhibit distinct rotational dynamics that are influenced by strain. Moreover, all studied clathrate hydrates are mechanically failed by fractures of water cage accompanied by formation of unconventional clathrate cages. Those findings give insights into understanding the structural, thermodynamic stability and mechanical properties of clathrate hydrates encapsulating fluorinated guests.