arXiv subjects

Thomas Petersen

Publications and source records attributed to Thomas Petersen.

3 recordsLinked to original sources

arXiv2025

Electrokinetic Effects on Flow and Ion Transport in Charge-Patterned Corrugated Nanochannels

The phase offset between surface charge modulation and geometric undulations in a corrugated nanochannel provides a tunable mechanism for rectified, diode-like ion transport under purely pressure-driven conditions: reversing the applied pressure gradient selectively activates transport of opposite ionic species, generating a net ionic current whose sign and magnitude are set by the charge-geometry alignment. Fully coupled Poisson-Nernst-Planck-Stokes simulations reveal the underlying two-regime structure: at low driving force (Regime I), throughput is suppressed below the Poiseuille limit by a localized streaming potential that pins counterions within the electric double layer; above a threshold pressure (Regime II), the mechanical force overcomes electrostatic resistance, producing an abrupt, orders-of-magnitude rise in mean velocity. Electroosmotically driven flow undergoes a qualitatively similar but smoother transition. Peak charge selectivity is achieved at near-complete electric double layer overlap and driving forces just below the Regime I-Regime II transition. Random walk particle tracking confirms selective rectification and quantifies the dependence of ion dispersion on surface charge placement across both regimes.

physics.flu-dyn↗

arXiv2023

Toward Modeling the Structure of Electrolytes at Charged Mineral Interfaces using Classical Density Functional Theory

The organization of water molecules and ions between charged mineral surfaces determines the stability of colloidal suspensions and the strength of phase-separated particulate gels. In this article we assemble a density functional that measures the free energy due to the interaction of water molecules and ions near electric double layers. The model accounts for the finite size of the particles using fundamental measure theory, hydrogen-bonding between water molecules using Wertheim's statistical association theory, long-range dispersion interactions using Barker and Henderson's high temperature expansion, electrostatic correlations using a functionalized mean-spherical approximation, and Coulomb forces through the Poisson equation. These contributions are shown to produce highly correlated structures, aptly rendering the layering of counter-ions and co-ions at highly charged surfaces, and permitting the solvation of ions and surfaces to be measured by a combination of short-ranged association and long-ranged attraction. The model is tested in a planar geometry near soft, charged surfaces to reproduce the structure of water near graphene and mica. For mica surfaces, explicitly representing the density of the outer oxygen layer of the exposed silica tetrahedra in the domain permits water molecules to hydrogen-bind to the surface. When electrostatic interactions are included, water molecules assume a hybrid character, being accounted for implicitly in the dielectric constant but explicitly otherwise. The disjoining pressure between approaching like-charged surfaces is calculated, demonstrating the model's ability to probe pressure oscillations that arise during the expulsion of ions and water layers from the interfacial gap, and predict the strong inter-attractive stresses that form at narrow interfacial spacing when the surface charge is overscreened.

cond-mat.soft↗

arXiv2018

Phase separation of stable colloidal clusters

This Article presents a nonequilibrium thermodynamic theory for the mean-field precipitation, aggregation and pattern formation of colloidal clusters. A variable gradient energy coefficient and the arrest of particle diffusion upon "jamming" of cluster aggregates in the spinodal region predicts observable gel patterns that, at high inter-cluster attraction, form system-spanning, out-of-equilibrium networks with glass-like, quasi-static structural relaxation. For reactive systems, we incorporate the free energy landscape of stable pre-nucleation clusters into the Allen-Cahn-Reaction equation. We show that pattern formation is dominantly controlled by the Damköhler number and the stability of the clusters, which modifies the auto-catalytic rate of precipitation. As clusters individually become more stable, bulk phase separation is suppressed.

cond-mat.soft↗