Clathrate formation and dissociation in vapour/water/ice/hydrate systems in SBA-15, Sol-Gel and CPG porous media, as probed by NMR relaxation, novel protocol NMR Cryoporometry, Neutron Scattering and ab-initio QM-MD simulation

The Gibbs Thomson effect modifies the pressure and temperature at which clathrates occur, hence altering the depth at which they occur in the sea-bed. NMR measurements as a function of temperature are being conducted for water/ice/hydrate systems in a range of pore geometries, including templated SBA-15 silicas, controlled pore glasses and sol-gel silicas. Rotator-phase plastic ice is shown to be present in confined geometry, and bulk tetrahydrofuran hydrate is also shown to probably have a rotator phase. A novel NMR Cryoporometry protocol has been developed that probes both the melting and freezing events, while avoiding the usual problem of supercooling for the freezing event. This enables a detailed probing of the system for a given pore size and geometry, and exploration of the differences between the hydrate formation and dissociation processes inside the pores. These process differences have an important effect for the environment, as they impact on the ability of a marine hydrate system to re-form once warmed above a critical temperature. Ab-Initio Quantum-Mechanical Molecular-Dynamics calculations are also being employed to probe the dynamics of liquids in pores at nanometric dimensions.