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At least 487 records · Page 27
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Hydrophobic Solvation of Gases (CO 2 , CH 4 , H 2 , Noble Gases) in Clay Interlayer Nanopores

In the past few years, experimental studies have shown that CO 2 is roughly 5 times more soluble in water-saturated clay interlayer water than in bulk liquid water. The fundamental basis of this selectivity remains unknown, as does its relevance to other gases. Here, we use molecular dynamics (MD) simulations and gravimetric adsorption experiments to determine the solubilities of CO 2 , CH 4 , H 2 , and noble gases in clay interlayer water. Our results confirm that clay minerals, despite their well-known hygroscopic nature, have a significant hydrophobic character at the atomistic scale. The affinity of dissolved gases for the clay surface shows significant variations related to the size and shape of the adsorbing molecules and the structuring of interfacial water by clay surfaces. Our results indicate that dissolved gases likely do not behave as inert tracers in fine-grained sedimentary rocks such as shale and mudstone, as routinely assumed in groundwater hydrology studies. Lastly, our results have implications for the fundamental science of hydrophobic adsorption, for the use of dissolved gases as tracers of fluid migration in the subsurface, and for low-carbon energy technologies that rely on fine-grained sedimentary rocks, such as carbon capture and storage, nuclear energy, and the transition from coal to natural gas.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Frustrated Solvation Structures Can Enhance Electron Transfer Rates

Polar surfaces can interact strongly with nearby water molecules, leading to the formation of highly ordered interfacial hydration structures. This ordering can lead to frustration in the hydrogen bond network, and, in the presence of solutes, frustrated hydration structures. We study frustration in the hydration of cations when confined between sheets of the water oxidation catalyst manganese dioxide. Frustrated hydration structures are shown to have profound effects on ion-surface electron transfer through the enhancement of energy gap fluctuations beyond those expected from Marcus theory. These fluctuations are accompanied by a concomitant increase in the electron transfer rate in Marcus’s normal regime. We demonstrate the generality of this phenomenon—enhancement of energy gap fluctuations due to frustration—by introducing a charge frustrated XY model, likening the hydration structure of confined cations to topological defects. Here, our findings shed light on recent experiments suggesting that water oxidation rates depend on the cation charge and Mn-oxidation state in these layered transition metal oxide materials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Solvents Polarity Governs Ion Interactions and Transport in a Solvated Room Temperature Ionic Liquid

We explore the influence of the solvent dipole moment on cation anion interactions and transport in 1-butyl-3-methyl-imidazolium bis-(trifluoromethylsulfonyl), [BMIM+][Tf2N ]. Free energy profiles derived from atomistic molecular dynamics (MD) simulations show a correlation of the cation anion separation and the equilibrium depth of the potential of mean force with the dipole moment of the solvent. Correlations of the ion diffusivity with the dipole moment and the concentration of the solvent were further demonstrated by classical MD simulations. Quasi-elastic neutron scattering experiments with deuterated solvents reveal a complex picture of nanophase separation into the ionic liquid-rich and solvent-rich phases. The experiment corroborates the trend of concentration- and dipole moment-dependent enhancement of ion mobility by the solvent, as suggested by the simulations. Despite the considerable structural complexity of ionic liquid solvent mixtures, we can rationalize and generalize the trends governing ionic transport in these complex electrolytes.

Osti, Naresh C↗