arXiv subjects

Anastasia G. Ilgen

Publications and source records attributed to Anastasia G. Ilgen.

4 recordsLinked to original sources

arXiv2026

Connecting Microseismicity to Lithology via a Model of Slip Avalanches

Fluid injection into the earth's crust can induce small and frequent earthquakes in the subsurface. Predicting their sizes and temporal occurrences via statistical analysis is crucial for safe operations in unconventional oil and gas recovery, enhanced geothermal systems, and geologic carbon storage. Here we show that a simple micromechanical model of slip avalanches in slowly deforming solids predicts the slip statistics observed over drastically different spatial scales, namely meter-scale microseismic observations and nanometer- to micrometer-scale nanoindentation experiments can be described with this model. Microseismic catalogs extracted from high-pressure fluid injection operations into geological basins with various lithologies and nanoindentation experiments on shale across a wide range of temperatures and mineral compositions yield statistics consistent with model predictions. This universality across materials, temperatures, and scales is consistent with the prediction that the slip statistics result from only a few basic properties. Previously debated deviations of the statistics in layered sedimentary formations are explained by finite-size and stress-integrative effects resulting from mechanically weak bedding planes. The slip statistics therefore provide important information about the structure and scales of the bedding planes. Conversely, the basin structure can also be used to predict the probability distribution for the sizes of triggered microseismic events.

cond-mat.other↗

arXiv2022

Adsorption at Nanoconfined Solid-Water Interfaces

Reactions at solid-water interfaces play a foundational role in water treatment systems, catalysis, chemical separations, and in predicting chemical fate and transport in the environment. Over the last century, experimental measurements and computational models have made tremendous progress in capturing reactions at solid surfaces. The interfacial reactivity of a solid surface, however, can change dramatically and unexpectedly when it is confined to the nanoscale. Nanoconfinement can arise in different geometries such as pores/cages (3-D confinement), channels (2-D confinement) and slits (1-D confinement). Therefore, measurements on unconfined surfaces, and molecular models parameterized based on these measurements, fail to capture chemical behaviors under nanoconfinement. This review evaluates recent experimental and theoretical advances, with a focus on adsorption at solid-water interfaces. We review how nanoconfinement alters the physico-chemical properties of water, and how the structure and dynamics of nanoconfined water dictate energetics, pathways, and products of adsorption in nanopores. The implications of these findings and future research directions are discussed.

physics.chem-ph↗

arXiv2021

Interplay of Physically Different Properties Leading to Challenges in Separating Lanthanide Cations -- an Ab Initio Molecular Dynamics and Experimental Study

The lanthanide elements have well-documented similarities in their chemical behavior, which makes the valuable trivalent lanthanide cations (Ln(III)) particularly difficult to separate from each other in water. In this work, we apply ab initio molecular dynamics simulations to compare the free energies (Delta G(ads)) associated with the adsorption of lanthanide cations to silica surfaces at a pH condition where SiO- groups are present. The predicted Delta G(ads) for lutetium (Lu(III)) and europium (Eu(III)) are similar within statistical uncertainties; this is in qualitative agreement with our batch adsorption measurements on silica. This finding is remarkable because the two cations exhibit hydration free energies (Delta G(hyd}) that differ by >2 eV, different hydration numbers, and different hydrolysis behavior far from silica surfaces. We observe that the similarity in Lu(III) and Eu(III) Delta G(ads) is the result of a delicate cancellation between the difference in Eu(III) and Lu(III) hydration (Delta G(hyd})), and their difference in binding energies to silica. We propose that disrupting this cancellation at the two end points, either for adsorbed or completely desorbed lanthanides (e.g., via nanoconfinment or mixed solvents), will lead to effective Ln separation.

cond-mat.mtrl-sci↗

arXiv2018

Concerted Metal Cation Desorption and Proton Transfer on Deprotonated Silica Surfaces

The adsorption equilibrium constants of monovalent and divalent cations to material surfaces in aqueous media are central to many technological, natural, and geochemical processes. Cation adsorption/desorption is often proposed to occur in concert with proton-transfer on hydroxyl-covered mineral surfaces, but so far this cooperative effect has been inferred indirectly. This work applies Density Functional Theory (DFT)-based molecular dynamics simulations of explicit liquid water/mineral interfaces to calculate metal ion desorption free energies. Monodentate adsorption of Na(+), Mg(2+), and Cu(2+) on partially deprotonated silica surfaces are considered. Na(+) is predicted to be unbound, while Cu(2+) exhibits larger binding free energies to surface SiO(-) groups than Mg(2+). The predicted trends agree with competitive adsorption measurements on fumed silica surfaces. As desorption proceeds, Cu(2+) dissociates one of the H2O molecules in its first solvation shell, turning into Cu(2+)O(-)(H2O)(3), while Mg remains Mg(2+)(H2O)(6). The protonation state of the SiO(-) group at the initial binding site does not vary monotonically with cation desorption.

physics.chem-ph↗