arXiv subjects

Aurora E. Clark

Publications and source records attributed to Aurora E. Clark.

5 recordsLinked to original sources

arXiv2026

Effect of cations on van der Waals interactions between particles in aqueous alkali nitrate electrolytes

The van der Waals interaction has been extensively studied for colloidal forces and resultant emergent phenomena such as colloidal stability, aggregation, and suspension rheology, but the effect of electrolytes on this interaction, especially at intermediate and high electrolyte concentrations, remains incompletely understood. We have extended the Lifshitz theory for van der Waals interactions in pure water to alkali nitrate solutions at arbitrary concentrations by developing a dielectric response model for alkali nitrate solutions that is based on electronic structure calculations of the molecular constituents. Due to their importance in catalysis, ceramics, and coating technologies, the Hamaker constants for rutile, boehmite, and alumina nanoparticles suspended in alkali nitrate solutions are calculated as a function of salt concentration. Contrary to prevailing assumptions, increasing the concentration of sodium (Na), potassium (K), and rubidium (Rb) nitrate solutions causes appreciable increases of the Hamaker constants relative to pure water instead of decreases, whereas cesium nitrate (CsNO3) has almost no effect on the Hamaker constant. We discussed the influence of the solution molar volume, the polarizability of the dissolved ions, and optical properties of the interacting particles in the context of previously published work. Our study indicates a non-vanishing role of van der Waals interactions on colloidal stability at intermediate and high electrolyte concentrations, leading to physical insights on emergent phenomena associated with nanoparticles.

cond-mat.soft↗

arXiv2023

Atomic-scale Mapping Unravel Anisotropic Dissolution Behaviors of Gibbsite Nanosheets

This study examines the anisotropic dissolution of the basal plane gibbsite (γ-Al(OH)3) nanoplates in sodium hydroxide solution using in situ atomic force microscopy (AFM) and density functional theory (DFT) calculations. In the surface-reaction controlled regime, in situ AFM measurements reveal anisotropic dissolution of hillocks and etch pits on the gibbsite basal plane, with preferred dissolution directions alternating between layers. The mirror-symmetric pattern of dissolution preference between adjacent gibbsite aluminum hydroxide sheet, observed along the crystallographic a-c plane, results from the matching symmetry between the structures of the adjacent (001) and (002) crystal planes. Consequently, the overall dissolution rate of gibbsite nanoplates exhibits crystallographic a-c plane symmetry, as the rate of parallel steps is governed by the slower ones. DFT calculations suggest that the anisotropic dissolution is partially due to the orientation and strength of Al-OH-Al linkages pair within gibbsite surface structure. These findings offer a comprehensive understanding of anisotropic dissolution behavior of gibbsite and illuminate the mechanisms behind preferential dissolution.

cond-mat.mtrl-sci↗

arXiv2019

$^{27}\text{Al }$ NMR chemical shift of $\text{Al}(\text{OH})_{4}^{-}$ from first principles. Assessment of error cancellation in NMR chemical shift computations in chemically distinct reference and targeted systems

Predicting accurate NMR chemical shieldings relies upon cancellation of different types of error in the ab initio methodology used to calculate the shielding tensor of the analyte of interest and the reference. Often the intrinsic error in computed shieldings due to basis sets, approximations in the Hamiltonian, description of the wave function, and dynamic effects, is nearly identical between the analyte and reference, yet if the electronic structure or sensitivity to local environment differs dramatically, this cannot be taken for granted. Detailed prior work has examined the octahedral trivalent cation $\text{Al}(\text{H}_{2}\text{O})_{6}^{3+}$ , accounting for ab initio intrinsic errors. However, the fact that this analyte is used as a reference for the chemically distinct tetrahedral anion $\text{Al}(\text{OH})_{4}^{-}$ inspires the study of how these errors cancel in an attempt to understand the limits of predictive capability for accurately determining $^{27}\text{Al }$ shielding in $\text{Al}(\text{OH})_{4}^{-}$. In this work, we estimate the absolute shielding of $^{27}\text{Al }$ nucleus in $\text{Al}(\text{OH})_{4}^{-}$ at the coupled cluster level (515.1 $\pm$ 5.3 ppm). Shielding sensitivity to the choice of method approximation and atomic basis sets treatment has been evaluated. Solvent and thermal effects are assessed through ensemble averaging techniques using ab-initio molecular dynamics. The contribution of each type of intrinsic error is assessed for $\text{Al}(\text{H}_{2}\text{O})_{6}^{3+}$ and $\text{Al}(\text{OH})_{4}^{-}$ ions, revealing significant differences that fundamentally hamper the ability to accurately calculate the $^{27}\text{Al }$ chemical shift of $\text{Al}(\text{OH})_{4}^{-}$ from first principles.

physics.chem-ph↗

arXiv2018

Heavy Anionic Complex Creates a Unique Water Structure at a Soft Charged Interface

Ion hydration and interfacial water play crucial roles in numerous phenomena ranging from biological to industrial systems. Although biologically relevant (and mostly smaller) ions have been studied extensively in this context, very little experimental data exist about molecular scale behavior of heavy ions and their complexes at interfaces, especially under technologically significant conditions. It has recently been shown that PtCl62- complexes adsorb at positively charged interfaces in a two-step process that cannot fit into well-known empirical trends, such as Hofmeister series. Here, a combined vibrational sum frequency generation and molecular dynamics study reveals that a unique interfacial water structure is connected to this peculiar adsorption behavior. A novel sub-ensemble analysis of MD simulation results show that after adsorption, PtCl62- complexes partially retain their first and second hydration spheres, and it is possible to identify three different types of water molecules around them based on their orientational structures and hydrogen bonding strengths. These results have important implications for relating interfacial water structure and hydration enthalpy to the general understanding of specific ion effects. This in turn influences interpretation of heavy metal ion distribution across and reactivity within, liquid interfaces.

cond-mat.soft↗

arXiv2018

Global topology of contact force networks: new insight into shear thickening suspensions

Highly concentrated or 'dense" particle suspensions can undergo a sharp increase in viscosity, or shear thickening, under applies stress. Understanding the fundamental features leading to such rheological changes in dense suspensions is crucial to optimize flow conditions or to design flow modifiers for slurry processing. While local changes to the particle environment under an applied shear can be related to changes in viscosity, there is a broader need to connect the shear thickening transition to the fundamental organization of particle-interaction forces which lead to long-range organization. In particular, at a high volume fraction of particles, recent evidence indicates frictional forces between contacting particles is of importance. Herein, the network of frictional contact forces is analyzed within simulated two-dimensional shear thickening suspensions. Two topological metrics are studied to characterize the response of the contact force network (CFN) under varying applied shear stress. The metrics, geodesic index and the void parameter, reflect complementary aspects of the CFN: one is the connectedness of the contact network and the second is the distribution of spatial areas devoid of particle-particle contacts. Considered in relation to the variation of the viscosity, the topological metrics show that the network grows homogeneously at large scales but with many local regions devoid of contacts, indicating clearly the role of stress chain growth in causing the large change in the rheological response at the shear thickening transition.

cond-mat.soft↗