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Disputation Philip Loche

06.12.2021 | 14:00
Titel der Dissertation:
Electrostatics at Aqueous Interfaces and in Nanoconfinement
Abstract: One molecule of utmost importance in natural science is liquid water. An exact electrostatic description of water and its interaction with other dissolved molecules or ions is usually impossible due to the complex structure of the liquid. Therefore, we are usually content with a continuum description by treating water as an unstructured homogenous – dielectric – material, already explaining several phenomena like solvation or precipitation. However, it is known that at interfaces the isotropy and homogeneity of the water's dielectric properties break down. Any modification of the dielectric constant at interfaces or in confined space fundamentally influences all electrostatic interactions including equilibria of chemical reactions or particle distributions. We present how the electrostatic interactions are modified in aqueous nano systems and how well a dielectric continuum description performs. The dielectric properties of water and ions are quantified using classical atomistic simulations as well as using a novel anisotropic linear continuum description and compared to recent experiments. For an accurate comparison, we develop a new simulation force field describing the physics of several monovalent ions in water with higher accuracy compared to previous parametrizations. Studying the water properties at planar interfaces, in narrow planar and cylindrical channels, we find that dielectric effects differ in perpendicular and parallel surface direction but decay to the bulk value within 1–2 nm away from the surface. This universal scaling exists regardless of the studied surface type. Based on the dielectric properties extracted from the simulations we analytically calculate interactions of charges with surfaces, evaporation rates of ions and the interaction between ions in planar as well as cylindrical geometry. By comparing the analytic predictions to explicit simulations, we quantify the breakdown of linear response theory at interfaces and reveal that interactions in confinement are drastically enhanced compared to non-confined systems.

Zeit & Ort

06.12.2021 | 14:00

Raum 1.1.16*
(Fachbereich Physik, Arnimallee 14, 14195 Berlin)
(*Teilnahme nur unter der strikten Einhaltung des geltenden Hygieneplans des Fachbereichs möglich)