Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Surface wetting – tracking down the causes of polar hydrophobicity

12.05.2016

The question of whether a liquid beads or adheres to a surface plays a role in almost all branches of industry. Researchers from the Fraunhofer Institute for Mechanics of Materials IWM in Freiburg and ExxonMobil Research & Engineering in New Jersey have now developed a multiscale simulation method for predicting the wetting behavior of liquids on surfaces. In a recent edition of the Journal of the American Chemical Society, the research team applied this methodology to the previously unexplained phenomenon of polar hydrophobicity in fluorinated carbon surfaces.

The research team, comprising Dr. Leonhard Mayrhofer, Dr. Gianpietro Moras, Dr. Narasimham Mulakaluri, and group manager Prof. Michael Moseler from the Fraunhofer IWM, MikroTribologie Centrum µTC, as well as Dr. Srinivasan Rajagopalan and Dr. Paul A. Stevens from Corporate Strategic Research, ExxonMobil Research & Engineering, can point to success at several levels.


On the diamond surface (left) an adsorbed water molecule interacts with a strong electric field, at the fully fluorinated surface however, the water molecule adsorbs in a practically field free zone.

Fraunhofer Institute for Mechanics of Materials IWM

“For one thing, the behavior of liquids on surfaces can now be predicted by means of a quantum-mechanical description of the valence electrons,” says Mayrhofer, first author. For another, the researchers believe they can use their work to now close a gap in the understanding of polar hydrophobicity, as it is called, for fluorinated carbon surfaces – that had long remained an open question. This effect had already been observed when Roy Plunkett discovered Teflon® in 1938.

Teflon, like nearly all perfluorinated carbon materials, is remarkably water-repellent, i.e. hydrophobic. Although the carbon-fluorine bonding exhibits a high degree of polarity, water molecules of similarly strong polarity surprisingly do not bind well to the surface. The research team has now been able for the first time to explain the origin of this anomaly using its simulation. The unexpected beading of water on this class of surfaces can be explained by the rapid drop of the electric field in a dense lattice of C-F dipoles.

Intentionally adjusting wetting behavior on a surface

The scientists studied the binding of water to a fluorinated diamond surface with the help of multiscale simulation. In order to estimate the binding energy, they studied the adherence of individual water molecules on the surface as a first step using quantum-mechanical calculations of the electronic structure. “We also wanted to understand the effect at the fundamental level,” according to Moras.

“With that as a starting point, we then scaled up the simulation to many water molecules so that the behavior of water drops can be mapped.” The insights from the multiscale model are far-reaching. “It becomes clear from our simulation that for a 100% fluorinated, extremely polarized surface, the electric dipole fields of the molecules are superposed in such a way that the electrostatic interaction falls off extremely rapidly, and the water is unable to adhere,” explains Mayrhofer.

This rapid fall-off of the electric field had already been predicted by Lennard-Jones in 1928 for dense lattices of mathematical dipoles, but until now had not been associated with polar hydrophobicity. The scientists carried out the same simulation for a surface that was 50 percent fluorinated. This showed that the behavior of the water molecules changed depending on how densely the dipole lattice was packed with fluorine at the surface. “We are able to adjust the contact angle of the water drops in this way," explains Mayrhofer. The greater the contact angle is, the less the water adheres to the surface.

The simulation can be carried out for any surface and liquid

What is now crucial: this simulation method allows for the prediction of the wetting behavior of arbitrary surfaces/liquids combinations. The wetting of surfaces plays a role in many areas. Mayrhofer and his colleagues can describe the behavior of oils on engine parts just as easily as that of bacterially contaminated liquids on medical equipment. “The first step to application development is a better understanding of fundamentals. With the framework developed in this collaborative study, we are able to better understand how to control surface-liquid interactions,” says Dr. Rajagopalan from ExxonMobil, “and this knowledge can enable design of optimal surface chemistry for specific applications.”

Weitere Informationen:

http://pubs.acs.org/doi/abs/10.1021/jacs.5b04073 - Publication in J. Am. Chem. Soc., 2016, 138 (12), pp 4018–4028, DOI: 10.1021/jacs.5b04073
http://www.en.iwm.fraunhofer.de - Fraunhofer Institute for Mechanics of Materials IWM

Katharina Hien | Fraunhofer-Institut für Werkstoffmechanik IWM

More articles from Information Technology:

nachricht Deep Learning predicts hematopoietic stem cell development
21.02.2017 | Helmholtz Zentrum München - Deutsches Forschungszentrum für Gesundheit und Umwelt

nachricht Sensors embedded in sports equipment could provide real-time analytics to your smartphone
16.02.2017 | University of Illinois College of Engineering

All articles from Information Technology >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Breakthrough with a chain of gold atoms

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

Im Focus: DNA repair: a new letter in the cell alphabet

Results reveal how discoveries may be hidden in scientific “blind spots”

Cells need to repair damaged DNA in our genes to prevent the development of cancer and other diseases. Our cells therefore activate and send “repair-proteins”...

Im Focus: Dresdner scientists print tomorrow’s world

The Fraunhofer IWS Dresden and Technische Universität Dresden inaugurated their jointly operated Center for Additive Manufacturing Dresden (AMCD) with a festive ceremony on February 7, 2017. Scientists from various disciplines perform research on materials, additive manufacturing processes and innovative technologies, which build up components in a layer by layer process. This technology opens up new horizons for component design and combinations of functions. For example during fabrication, electrical conductors and sensors are already able to be additively manufactured into components. They provide information about stress conditions of a product during operation.

The 3D-printing technology, or additive manufacturing as it is often called, has long made the step out of scientific research laboratories into industrial...

Im Focus: Mimicking nature's cellular architectures via 3-D printing

Research offers new level of control over the structure of 3-D printed materials

Nature does amazing things with limited design materials. Grass, for example, can support its own weight, resist strong wind loads, and recover after being...

Im Focus: Three Magnetic States for Each Hole

Nanometer-scale magnetic perforated grids could create new possibilities for computing. Together with international colleagues, scientists from the Helmholtz Zentrum Dresden-Rossendorf (HZDR) have shown how a cobalt grid can be reliably programmed at room temperature. In addition they discovered that for every hole ("antidot") three magnetic states can be configured. The results have been published in the journal "Scientific Reports".

Physicist Dr. Rantej Bali from the HZDR, together with scientists from Singapore and Australia, designed a special grid structure in a thin layer of cobalt in...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Booth and panel discussion – The Lindau Nobel Laureate Meetings at the AAAS 2017 Annual Meeting

13.02.2017 | Event News

Complex Loading versus Hidden Reserves

10.02.2017 | Event News

International Conference on Crystal Growth in Freiburg

09.02.2017 | Event News

 
Latest News

Stingless bees have their nests protected by soldiers

24.02.2017 | Life Sciences

New risk factors for anxiety disorders

24.02.2017 | Life Sciences

MWC 2017: 5G Capital Berlin

24.02.2017 | Trade Fair News

VideoLinks
B2B-VideoLinks
More VideoLinks >>>