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
NASA laser communications to provide Orion faster connections
30.03.2017 | NASA/Goddard Space Flight Center
Pinball at the atomic level
30.03.2017 | Max-Planck-Institut für Struktur und Dynamik der Materie
The Institute of Semiconductor Technology and the Institute of Physical and Theoretical Chemistry, both members of the Laboratory for Emerging Nanometrology (LENA), at Technische Universität Braunschweig are partners in a new European research project entitled ChipScope, which aims to develop a completely new and extremely small optical microscope capable of observing the interior of living cells in real time. A consortium of 7 partners from 5 countries will tackle this issue with very ambitious objectives during a four-year research program.
To demonstrate the usefulness of this new scientific tool, at the end of the project the developed chip-sized microscope will be used to observe in real-time...
Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.
The results will be published on March 22 in the journal „Astronomy & Astrophysics“.
Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...
Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.
Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...
In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...
20.03.2017 | Event News
14.03.2017 | Event News
07.03.2017 | Event News
30.03.2017 | Physics and Astronomy
30.03.2017 | Studies and Analyses
30.03.2017 | Life Sciences