Physicists at the University of Zurich have developed a system that enables them to switch back and forth the adhesion and stiction (static friction) of a water drop on a solid surface. The change in voltage is expressed macroscopically in the contact angle between the drop and the surface. This effect can be attributed to the change in the surface properties on the nanometer scale.
How can a gecko move across a ceiling upside down? Two mechanisms are responsible: Adhesion via billions of extremely fine hairs on its feet, which enable it to stick to ceilings and walls. And as soon as the gecko moves, it relies on stiction. However, any change of adhesion and stiction at macroscopic level is expressed on the nanometer scale through the change in the forces exerted between atoms and molecules.
The boron nitride nanomesh superhoneycomb: nitrogen (green), boron (orange), rhodium (grey); distance between honeycombs 3.2 nm.
Marcella Iannuzzi, UZH & Ari Seitsonen, ENS Paris
How a drop of water touches a honeycomb structure
An international team of researchers headed by Thomas Greber from the University of Zurich’s Physik-Institut succeeded in changing the manner in which a drop of liquid adheres to a surface by altering the electric voltage applied to a water drop. The surface upon which the drop lies consists of a material known as nanomesh, a single boron nitride layer on metallic rhodium. The structure is shaped like honeycomb with a comb depth of 0.1 nanometers and comb-comb distance of 3.2 nanometers.
Macroscopically, the change in electrical voltage is expressed in the change of the contact angle between the drop and the nanomesh surface. The contact or wetting angle refers to the angle that a drop of liquid assumes with respect to the surface of a solid. This angle can be measured with the aid of backlit photographs.
Change in the surface structure alters the contact angle of the drop
On the nanometer scale, the change in voltage causes the following: The nitrogen bonds with the rhodium are replaced by hydrogen-rhodium bonds, which flattens the nanomesh structure. How strongly the boron nitride’s nitrogen binds to the surface of the rhodium depends on its distance from and direction to the next rhodium atom.
And this determines the honeycomb structure and depth of the boron nitride layer. If the voltage changes, hydrogen accumulates between the boron nitride and the rhodium layer, which causes the honeycomb boron nitride layer to become flat. Tunneling microscopy can be used to detect this nanoscopic effect – the change in the surface properties of the nanomesh – in the liquid.
“To understand and control the interplay between the macro and the nano-world is the real challenge in nanoscience,” stresses Greber. After all, six orders of magnitude need to be bridged – from millimeters in length (10-3 m) to nanometers (10-9 m); that’s a factor of one million. “Our model system of the electrically switchable nanomesh and a drop’s observable contact angle enables us to access the fundamental phenomenon of the friction of liquids on surfaces more precisely. This should help us solve problems that crop up during lubrication more effectively, for instance.” The research project actually appears on the cover of the latest issue of the renowned journal Nature.
On the one hand, the new system is interesting for biology. Applying this effect should make it possible to control the adhesion and movement of cells. Aspects such as cell migration or the formation of complex, multicellular structures with new scientific approaches might be researched as a result. On the other hand, technological applications such as capillary pumps, where the capillary height can be controlled via electrical voltage, or micro-capillaries, where the flow resistance can be controlled, are also conceivable.
Stijn F. L. Mertens, Adrian Hemmi, Stefan Muff, Oliver Gröning, Steven De Feyter, Jürg Osterwalder, Thomas Greber. Switching stiction and adhesion of a liquid on a solid. Nature. June 30, 2016. DOI: 10.1038/nature18275
About the study
The research results were achieved within the scope of the Sinergia Program of the Swiss National Science Foundation (SNSF). The SNSF uses this instrument to promote the collaboration between several research groups, which conduct research across disciplines with the prospect of ground-breaking results. Besides the University of Zurich, the Katholieke Universiteit Leuven, Vienna University of Technology and Empa were also involved.
Prof. Dr. Thomas Greber
University of Zurich
Phone: +41 44 635 57 44
Kurt Bodenmüller | Universität Zürich
Computer model predicts how fracturing metallic glass releases energy at the atomic level
20.07.2018 | American Institute of Physics
What happens when we heat the atomic lattice of a magnet all of a sudden?
18.07.2018 | Forschungsverbund Berlin
A new manufacturing technique uses a process similar to newspaper printing to form smoother and more flexible metals for making ultrafast electronic devices.
The low-cost process, developed by Purdue University researchers, combines tools already used in industry for manufacturing metals on a large scale, but uses...
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
13.07.2018 | Event News
12.07.2018 | Event News
03.07.2018 | Event News
20.07.2018 | Power and Electrical Engineering
20.07.2018 | Information Technology
20.07.2018 | Materials Sciences