About

Research in the “Liquid Electrolytes at Interfaces” group

We focus on soft matter, specifically phenomena that involve interfaces between liquid electrolytes, solids, and gases. In contrast to bulk liquids, interfaces introduce additional effects such as surface tension, electrostatic or electrochemical interactions. Our goal is to build a fundamental understanding of the physical-chemical porcesses at such interfaces based on first principles. To this end, we conduct experiments, continuum simulations, and theoretical analyses in order to develop simple models with high predictive power and broad applicability. 

Our research can be subdivided into different fields. This subdivision is by no means absolute as the different fields and topics can have substantial overlap.

Slide Electrification

When drops slide along solid surfaces, they can spontaneously acquire a charge and leave behind an opposite surface charge on the solid surface. This phenomenon, called Slide Electrification, is very general and has been observed on technical surfaces as well as natural surfaces such as plant leaves. 

Electrostatic effects have long been overlooked in the study of wetting phenomena. In the past decade, they have moved into the focus of intense research. Slide electrification is one of the most common effects introducing electrostatics into dynamic wetting problems. We are interested in understanding the fundamental processes leading to charging and quantiatively predicting them. 

Behavior of Charged Drops

Drops spontaneously charge during sliding, pipetting, spraying, jumping, or in thunderclouds. Consequently, charged drops are far more common than previously acknowledged and may in fact be the default while uncharged drops constitute a special case. 

It turns out that even small charges fundamentally alter the behavior of drops when they interact with surfaces. From their contact angles (the angle formed between the drop surface and the solid surface when sitting on a surface) to their splashing behavior during impact -- charged drops behave differently. We study phenomena in which electrostatic effects alter or even dominate the behavior of drops. 

Electrostatic Screening in Liquids

Fundamentally, electrostatic forces are long range. In liquids with ionic charge carriers, liquid electrolytes, however, electrostatic interactions are screened by so-called electric double layers: When a charged surface is in contact with a liquid electrolyte, the layer of charge on the surface attracts countercharges from the liquid and they form a diffuse layer with a thickness of around 1-1000 nm. This length scale limits the range of electrostatic interactions in liquids. 

While the electrostatic screening in liquid electrolytes has been studied for over a century, we stumbled over some cases where the established models do not match up with experimental observations. We are interested in understanding and modelling the electric double layer in cases beyond the validity of established models.

Electrokinetic Transport in Nanopores

Electrokinetics studies the movement of charges in materials that do not conduct electrons. We are mainly interested in the movement of ions in porous media. The relevance is immediate, ranging from charge transport in energy storage devices like supercapacitors, to brain-like computing and iontronics. 

We focus on theoretically modelling and simulating combined ion and fluid transport with continuum theory. The continuum approach bridges different length scales ranging from the thickness of electric double layers to the thickness of porous membranes and is especially powerful in predicting and modelling collective behavior that arises from combinations of the geometry, the materials, and applied stimuli. We study electroconvection in nanopores, relevant for nanopumps or the charging of energy storage devices, and ionic transport in novel technical membranes.