Berlin 2018 – scientific programme

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DY: Fachverband Dynamik und Statistische Physik

DY 29: Particulate Matter: From microscopic interactions to collective motion (joint session DY/CPP)

DY 29.7: Talk

Tuesday, March 13, 2018, 15:30–15:45, EB 107

In-cage dynamics of molecular hydrogen in clathrates hydrates as function of the confinement size — •Margarita Russina — Helmholtz Zentrum Berlin für Materialied und Energie, Hahn-Meitner Platz 1, 14109 Berlin

To understanding the criteria governing the molecular mobility in confinement we have studied in-cage dynamics of confined molecular hydrogen as a function of confinement size. We used nanopores ice based clathrate with nanocages of two different dimensions of 0.75 and 0.946 nm, which are particularly suitable model systems since the interactions between the clathrate framework and H2 are of the same hydrophobic nature in both cages. We have found that by varying the size of the pore by only 20 % in the effective radius we can modify the diffusive mobility of confined hydrogen in both directions, i.e. both reducing and enhancing mobility compared to the bulk. In the smaller cages of clathrate hydrates with a mean size of 0.795 nm we observe strong hydrogen localization in the cage center even at temperatures up to 200K. Moderate increase of the confinement to 0.946 nm leads to the onset of jump diffusion between tetrahedrally shaped sorption sites in large cages with separation length of about 2.79 Å already at T=10 K, where bulk hydrogen is frozen at ambient pressure. The observed difference in mobility between small and large cages can be understood as a dimensional phenomenon caused by the modulation of cage potentials as a function of the cage size.