Virtual fluid for the description of interfacial effects in metallic
materials

Date:
November 17, 2021
Source:
Universitaet Stuttgart
Summary:
A research group presents a new simulation method for describing
the attachment of a liquid to a surface.



FULL STORY ========================================================================== Liquids containing ions or polar molecules are ubiquitous in many
applications needed for green technologies such as energy storage, electrochemistry or catalysis. When such liquids are brought to an
interface such as an electrode - - or even confined in a porous material
-- they exhibit unexpected behavior that goes beyond the effects already
known. Recent experiments have shown that the properties of the employed material, which can be insulating or metallic, strongly influence the thermodynamic and dynamic behavior of these fluids. To shed more light
on these effects, physicists at the University of Stuttgart, Universite' Grenoble Alpes and Sorbonne Universite' Paris have developed a novel
computer simulation strategy using a virtual fluid that allows the electrostatic interactions within any material to be taken into account
while being computationally sufficiently efficient to study the properties
of fluids at such interfaces. The new method now made it possible for
the first time to study the wetting transition at the nanoscale. This
depends on whether the ionic liquid encounters a material that has
insulating or metallic properties.

This breakthrough approach provides a new theoretical framework for
predicting the unusual behavior of charged liquids, especially in contact
with nanoporous metallic structures, and has direct applications in the
fields of energy storage and environment.


========================================================================== Despite their key role in physics, chemistry and biology, the behavior
of ionic or dipolar liquids near surfaces -- such as a porous material
-- remains puzzling in many respects. One of the greatest challenges
in the theoretical description of such systems is the complexity of
the electrostatic interactions. For example, an ion in a perfect metal
produces an inverse counter-charge, which corresponds to the negative
mirror image. In contrast, no such image charges are induced in a
perfect insulator because there are no freely moving electrons. However,
any real, i.e., non-idealized material has properties that lie exactly
between the two previously mentioned asymptotes.

Accordingly, the metallic or insulating nature of the material
is expected to have a significant influence on the properties of the
adjacent fluid. However, established theoretical approaches reach their
limits here, since they assume either perfectly metallic or perfectly insulating materials. To date, there is a gap in the description when
it comes to explaining the observed surface properties of real materials
in which the mirror charges are sufficiently smeared out.

In their recent paper, published in Nature Materials, Dr. Alexander
Schlaich from the University of Stuttgart et al. present a new
atomic-scale simulation method that allows to describe the adsorption
of a liquid to a surface while explicitly considering the electron
distribution in the metallic material.

While common methods consider surfaces made of an insulating material or
a perfect metal, they have developed a method that mimics the effects
of electrostatic shielding caused by any material between these two
extremes. The essential point of this approach is to describe the
Coulombic interactions in the metallic material by a "virtual" fluid
composed of light and fast charged particles. These create electrostatic shielding by reorganizing in the presence of the fluid. This strategy
is particularly easy to implement in any standard atomistic simulation environment and can be easily transferred. In particular, this approach
allows the calculation of the capacitive behavior of realistic systems as
used in energy storage applications. As part of the SimTech cluster of excellence at the University of Stuttgart, Alexander Schlaich is using
such simulations of porous, conductive electrode materials to optimize
the efficiency of the next generation of supercapacitors, which can store enormous power density. The wetting behavior of aqueous salt solutions
in realistic porous materials is also the focus of his contribution
to the Stuttgart Collaborative Research Center 1313 "Interface-driven multi-field processes in porous media -- flow, transport and deformation," which also investigates precipitation and evaporation processes related
to soil salinization. The developed methodology is thus relevant for a
wide range of systems, as well as for further research at the University
of Stuttgart.

========================================================================== Story Source: Materials provided by Universitaet_Stuttgart. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Alexander Schlaich, Dongliang Jin, Lyderic Bocquet, Benoit Coasne.

Electronic screening using a virtual Thomas-Fermi fluid for
predicting wetting and phase transitions of ionic liquids at metal
surfaces. Nature Materials, 2021; DOI: 10.1038/s41563-021-01121-0 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/11/211117100111.htm

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