Molecular Dynamics simulations of high density hard sphere fluids clearly show a breakdown of the Stokes-Einstein equation (SE). This result has been conjectured to be due to the presence of mobile particles, i.e., ones which have the propensity to "hop" distances which are integer multiples of the interparticle distance. We conclusively show that, even though the whole liquid violates the SE equation at high densities, the sedentary particles, i.e., ones complementary to the "hoppers", obey the SE relationship.These results strongly support the notion that the unusual dynamics of fluids near vitrification are caused exclusively by the presence of hopping particles.

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To achieve the United Nations Climate Change Conference (COP-26) targets of net zero carbon emissions, hydrate-based carbon dioxide (CO 2 ) capture and sequestration (CCS) can be considered one of the potential sustainable technologies. However, the sluggish kinetics of CO 2 hydrate formation in the saline subsea environment and the nonecofriendly nature of the existing additives (kinetic promoters) are the major challenges. Therefore, to intensify the kinetics, the performance of the biocompatible hydrophobic amino acid Lleucine for CO 2 hydrate formation/dissociation was evaluated using the simulated subsea sediment of silica sand. Experiments were performed in saline (3.0 wt % NaCl) and nonsaline environments with L-leucine (0.1−1.0 wt %) at 3.2 ± 0.2 MPa pressure and 274.5 ± 0.2 K temperature. With the addition of 0.5 wt % L-leucine to freshwater, water-to-hydrate conversion of 73.01 ± 4.96% (44.08 ± 2.95% gas-to-hydrate conversion) was achieved with a rate of gas uptake of 4.25 ± 0.39 mmol/min, which is ∼10 times higher compared to the baseline (no promoter). Though salinity significantly reduced the hydrate formation kinetics, the addition of 1.0 wt % L-leucine intensified the rate of CO 2 uptake to 2.32 ± 0.319 mmol/min from 0.55 ± 0.033 mmol/min in saline water baseline. The enhanced kinetics reported in this work highlights the potential of engaging L-leucine in the hydrate-based CCS approach.

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