Mapping electrostatic potential in electrolyte solution

TL;DR

This paper demonstrates a novel liquid electron scattering method to measure electrostatic potential distribution and Debye screening length in electrolyte solutions at Angstrom scale, revealing concentration-dependent ion effects.

Contribution

It introduces a state-of-the-art relativistic electron beam technique to map ESP and extract dielectric functions in electrolyte solutions, advancing microscopic understanding.

Findings

Debye screening length varies with concentration

ESP measurement reveals long- and short-range ion effects

Method enables investigation of electrostatic origin of ion-specific phenomena

Abstract

Mapping the electrostatic potential (ESP) distribution around ions in electrolyte solution is crucial for the establishment of a microscopic understanding of electrolyte solution properties. For solutions in the bulk phase, it has not been possible to measure the ESP distribution on Angstrom scale. Here we show that liquid electron scattering experiment using state-of-the-art relativistic electron beam can be used to measure the Debye screening length of aqueous LiCl, KCl, and KI solutions across a wide range of concentrations. We observe that the Debye screening length is long-ranged at low concentration and short-ranged at high concentration, providing key insight into the decades-long debate over whether the impact of ions in water is long-ranged or short-ranged. In addition, we show that the measured ESP can be used to retrieve the non-local dielectric function of electrolyte solution, which can serve as a promising route to investigate the electrostatic origin of special ion effects. Our observations show that, interaction, as one of the two fundamental perspectives for understanding electrolyte solution, can provide much richer information than structure.