Swelling Phenomena of the Nonswelling Clay Induced by CO and Water Cooperative Adsorption in Janus-Surface Micropores.

With the development of microscopy and sensor techniques, it becomes evident that nonswelling clays show swelling behavior under CO-water mixture environments at high pressures and temperatures. The examples include Illite, muscovite, and kaolinite-rich rock samples. Here, we investigated the underlying mechanisms of kaolinite swelling induced by CO and water using molecular simulations and low-pressure gas adsorption experiments.

Modeling CO-Water-Mineral Wettability and Mineralization for Carbon Geosequestration.

Carbon dioxide (CO) capture and storage (CCS) is an important climate change mitigation option along with improved energy efficiency, renewable energy, and nuclear energy. CO geosequestration, that is, to store CO under the subsurface of Earth, is feasible because the world's sedimentary basins have high capacity and are often located in the same region of the world as emission sources. How CO interacts with the connate water and minerals is the focus of this Account.

Elasticity and Stability of Clathrate Hydrate: Role of Guest Molecule Motions.

Molecular dynamic simulations were performed to determine the elastic constants of carbon dioxide (CO) and methane (CH) hydrates at one hundred pressure-temperature data points, respectively. The conditions represent marine sediments and permafrost zones where gas hydrates occur. The shear modulus and Young's modulus of the CO hydrate increase anomalously with increasing temperature, whereas those of the CH hydrate decrease regularly with increase in temperature.

Ion Distribution and Hydration Structure in the Stern Layer on Muscovite Surface.

Based on molecular dynamics simulations of eight ions (Na, K, Rb, Cs, Mg, Ca, Sr, and Ba) on muscovite mica surfaces in water, we demonstrate that experimental data on the muscovite mica surface can be rationalized through a unified picture of adsorption structures including the hydration structure, cation heights from the muscovite surface, and state stability. These simulations enable us to categorize the inner-sphere surface complex into two different species: an inner-sphere surface complex in a ditrigonal cavity (IS1) and that on top of Al (IS2). By considering the presence of the two inner-sphere surface complexes, the experimental finding that the heights of adsorbed cations from the muscovite surface are proportional to the ionic radius for K and Cs but inversely proportional to the ionic radius for Ca and Ba was explained.

Molecular Dynamics Simulation of Atomic Force Microscopy at the Water-Muscovite Interface: Hydration Layer Structure and Force Analysis.

With the development of atomic force microscopy (AFM), it is now possible to detect the buried liquid-solid interfacial structure in three dimensions at the atomic scale. One of the model surfaces used for AFM is the muscovite surface because it is atomically flat after cleavage along the basal plane. Although it is considered that force profiles obtained by AFM reflect the interfacial structures (e.

Microscopic Origin of Strain Hardening in Methane Hydrate.

It has been reported for a long time that methane hydrate presents strain hardening, whereas the strength of normal ice weakens with increasing strain after an ultimate strength. However, the microscopic origin of these differences is not known. Here, we investigated the mechanical characteristics of methane hydrate and normal ice by compressive deformation test using molecular dynamics simulations.

Mechanisms for Enhanced Hydrophobicity by Atomic-Scale Roughness.

It is well known that the close-packed CF3-terminated solid surface is among the most hydrophobic surfaces in nature. Molecular dynamic simulations show that this hydrophobicity can be further enhanced by the atomic-scale roughness. Consequently, the hydrophobic gap width is enlarged to about 0.

Lattice Boltzmann simulations of supercritical CO2-water drainage displacement in porous media: CO2 saturation and displacement mechanism.

CO2 geosequestration in deep aquifers requires the displacement of water (wetting phase) from the porous media by supercritical CO2 (nonwetting phase). However, the interfacial instabilities, such as viscous and capillary fingerings, develop during the drainage displacement. Moreover, the burstlike Haines jump often occurs under conditions of low capillary number.

Molecular dynamics study of salt-solution interface: solubility and surface charge of salt in water.

The NaCl salt-solution interface often serves as an example of an uncharged surface. However, recent laser-Doppler electrophoresis has shown some evidence that the NaCl crystal is positively charged in its saturated solution. Using molecular dynamics (MD) simulations, we have investigated the NaCl salt-solution interface system, and calculated the solubility of the salt using the direct method and free energy calculations, which are kinetic and thermodynamic approaches, respectively.

Asymmetric orientation of toluene molecules at oil-silica interfaces.

The interfacial structure of heptane and toluene at oil-silica interfaces has previously been studied by sum frequency generation [Z. Yang et al., J.

Comparison of thermodynamic stabilities and mechanical properties of CO2, SiO2, and GeO2 polymorphs by first-principles calculations.

The recent discovery that molecular CO(2) transforms under compression into carbon four-coordinated, 3-dimensional network solid phases has generated considerable interests on possible new phases in the fourth-main-group elemental oxides. Based on density-functional theory calculations, we have investigated the thermodynamic stability, mechanical properties and electronic structure of proposed guest-free clathrates, quartz and cristobalite phases for CO(2), SiO(2), and GeO(2), and the dry ice phase for CO(2). It was predicted that a GeO(2) clathrate, likely a semiconductor, could be synthesized presumably with some suitable guest molecules.

Self-accumulation of aromatics at the oil-water interface through weak hydrogen bonding.

It is well-known that the amphiphilic solutes are surface-active and can accumulate at the oil-water interface. Here, we have investigated the water and a light-oil model interface by using molecular dynamic simulations. It was found that aromatics concentrated in the interfacial region, whereas the other hydrocarbons were uniformly distributed throughout the oil phase.