Nano- und Mikrofluidik

Nano- und Mikrofluidik

Willkommen auf den Seiten des Fachgebiets „Nano- und Mikrofluidik“! Bitte nehmen Sie mit uns Kontakt auf, falls Sie Vorschläge, Anregungen für Forschungskooperationen, allgemeine oder spezielle Fragen haben.

Wir beschäftigen uns mit Transportphänomenen in Fluiden auf der Nano- und Mikrometerskala. Dabei interessiert uns besonders die Erforschung von Grundlagen mit der Intention, den Weg für neuartige Anwendungen zu bereiten. Unsere Forschung erstreckt sich über ein breites Themenspektrum und kombiniert experimentelle, theoretische und numerische Ansätze. Zu unseren Arbeitsgebieten gehören Gaskinetik auf der Nanoskala, Elektrokinetik, Grenzflächenströmungen, Benetzungsphänomene und Trennprozesse für Biomoleküle.

News

Sept 15, 2016

Humboldt Fellow Professor Dominik Barz

On Sept 1, 2016, Professor Dominik Barz of Queen’s University/Canada joined our group. He is supported by the Humboldt Foundation and pursues a research program in the field of electrokinetic flows. We are looking forward to a fruitful co-operation.

July 04, 2016

GIF Research Grant

We have won a research grant by the German Israeli Foundation (GIF). Together with Dr. Moran Bercovici from the Israel Institute of Technology we will study methods for tailoring and reconfiguring complex electroosmotic flow patterns in a channel-free microfluidic device.

June 03, 2016

Thermoelectricity in confined liquid electrolytes

The electric field induced in a bulk phase of a liquid electrolyte exposed to a temperature gradient is attributed to different thermophoretic mobilities of the dissolved ion species. We have shown that such Soret-type ion thermodiffusion is not required to induce thermoelectricity even in the simplest electrolyte if it is confined between walls carrying a charge density. The space charge of the electric double layer leads to selective ion diffusion driven by a temperature-dependent electrophoretic ion mobility, which —for narrow channels— may cause thermovoltages larger in magnitude than for the classical Soret effect. On the left, the corresponding (scaled) Seebeck coefficient is plotted for different values of the surface charge density against the (scaled) channel width.

Reference: M. Dietzel and S. Hardt, Thermoelectricity in confined liquid electrolytes, Physical Review Letters 116, 225901 (2016)

February 19, 2016

Stokes drag on a sphere translating along a fluid-fluid interface

Presumably the most well-known achievement of George Gabriel Stokes is his formula for the drag force experienced by a sphere translating in an unbounded fluid at low Reynolds numbers. However, in some scenarios small particles are attached to an interface between two immiscible fluids, constrained to tangential motion relative to the interface. We have analyzed this situation and derived a generalization of Stokes’ law for large viscosity contrast and small capillary number. The image at the left is a sketch of the corresponding streamlines.

Reference: A. Dörr, S. Hardt, H. Masoud and H. A. Stone, Drag and diffusion coefficients of a spherical particle attached to a fluid interface, Journal of Fluid Mechanics 790 (2016), 607–618.

October 26, 2015

Structuring thin liquid films utilizing the Bénard-Marangoni instability

If a system of two superposed liquid films is exposed to a temperature gradient normal to the films, the upper layer exhibits convection cells which deform the lower thin film in an identical pattern. This effect can be seen in the figure above, which displays the hexagonal convection cells and the humps of the thin film below. The principle could find applications in fabricating regular, highly ordered surface structures.

Reference: I.Nejati, M. Dietzel and S. Hardt, Conjugated liquid layers driven by the short-wavelength Bénard-Marangoni instability: experiment and numerical simulation, J. Fluid Mech., 783 (2015), 46-71.

July 01, 2015

Institute for Nano- and Microfluidics participates in LOEWE Cluster CompuGene

Yesterday the government of the federal state of Hessen approved approx. 4.4 million Euros funding for the LOEWE Cluster CompuGene. CompuGene will focus on the development of artificial genetic circuits which may be employed for various purposes, for example for the production of certain rare substances. We will contribute by exploring microfluidic methods for studying genetic circuits in a scenario as close as possible to in vivo conditions.

April 07, 2015

Results on motion of a microsphere along a fluid interface published in Journal of Fluid Mechanics

A microsphere driven along an interface between two fluids of highly different viscosities experiences a drag force differing from the well-known Stokes drag. Additionally, the viscous flow around the moving particle deforms the fluid-fluid interface from its equilibrium shape while the particle assumes a tilted orientation. The figure below depicts a spherical particle with a pinned three-phase contact line moving from left to right with the lower fluid having higher viscosity than the upper. The corresponding deformation of the fluid interface results in a pair interaction between particles.

Reference: A. Dörr and S. Hardt, Driven particles at fluid interfaces acting as capillary dipoles, J. Fluid Mech. 770 (2015), 5-26.