Role of Guest Molecules in the Mechanical Properties of Clathrate Hydrates

Clathrate hydrates (CHs) are promising molecular structures for versatile applications such as gas capture and storage, cold storage, and gas separation. Understanding the mechanical responses is of importance for utilizing and predicting the stability of their formations, but remains very limited. Here, mechanical characteristics of CHs entrapping a variety of gas molecules are investigated by molecular dynamics (MD) simulations. All studied CHs are structurally stable host-host hydrogen (H)-bonds yet show distinct host-guest interaction energies under load-free conditions. Tension MD simulations reveal that the tensile strength and Youngs modulus of CHs depend not only on the size and shape of guest molecules but also on their polarity; however, all CHs undergo brittle fracture on either the (0 0 1) or (1 0 1) plane also relying on the type of guest molecules. Interestingly, elastic deformation of CHs causes a reduction in the number of H-bonds, yet stronger interaction of specific triatomic guest molecules@5(12) with the surrounding host-water molecules, in contrast to the case of those @5(12)6(2). Structural analysis shows that multiatomic guest molecules@cages uniquely reorient due to misshaping of cages, and H-bonded angular deformation of water-cages plays a more crucial role in the elastic responses of CHs than straining of H-bonds.