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 Stable magnetic bit of three atoms
21.09.2017 | Sonderforschungsbereich 668

nachricht Drones can almost see in the dark
20.09.2017 | Universität Zürich

All articles from Information Technology >>>

The most recent press releases about innovation >>>

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

Im Focus: LaserTAB: More efficient and precise contacts thanks to human-robot collaboration

At the productronica trade fair in Munich this November, the Fraunhofer Institute for Laser Technology ILT will be presenting Laser-Based Tape-Automated Bonding, LaserTAB for short. The experts from Aachen will be demonstrating how new battery cells and power electronics can be micro-welded more efficiently and precisely than ever before thanks to new optics and robot support.

Fraunhofer ILT from Aachen relies on a clever combination of robotics and a laser scanner with new optics as well as process monitoring, which it has developed...

Im Focus: The pyrenoid is a carbon-fixing liquid droplet

Plants and algae use the enzyme Rubisco to fix carbon dioxide, removing it from the atmosphere and converting it into biomass. Algae have figured out a way to increase the efficiency of carbon fixation. They gather most of their Rubisco into a ball-shaped microcompartment called the pyrenoid, which they flood with a high local concentration of carbon dioxide. A team of scientists at Princeton University, the Carnegie Institution for Science, Stanford University and the Max Plank Institute of Biochemistry have unravelled the mysteries of how the pyrenoid is assembled. These insights can help to engineer crops that remove more carbon dioxide from the atmosphere while producing more food.

A warming planet

Im Focus: Highly precise wiring in the Cerebral Cortex

Our brains house extremely complex neuronal circuits, whose detailed structures are still largely unknown. This is especially true for the so-called cerebral cortex of mammals, where among other things vision, thoughts or spatial orientation are being computed. Here the rules by which nerve cells are connected to each other are only partly understood. A team of scientists around Moritz Helmstaedter at the Frankfiurt Max Planck Institute for Brain Research and Helene Schmidt (Humboldt University in Berlin) have now discovered a surprisingly precise nerve cell connectivity pattern in the part of the cerebral cortex that is responsible for orienting the individual animal or human in space.

The researchers report online in Nature (Schmidt et al., 2017. Axonal synapse sorting in medial entorhinal cortex, DOI: 10.1038/nature24005) that synapses in...

Im Focus: Tiny lasers from a gallery of whispers

New technique promises tunable laser devices

Whispering gallery mode (WGM) resonators are used to make tiny micro-lasers, sensors, switches, routers and other devices. These tiny structures rely on a...

Im Focus: Ultrafast snapshots of relaxing electrons in solids

Using ultrafast flashes of laser and x-ray radiation, scientists at the Max Planck Institute of Quantum Optics (Garching, Germany) took snapshots of the briefest electron motion inside a solid material to date. The electron motion lasted only 750 billionths of the billionth of a second before it fainted, setting a new record of human capability to capture ultrafast processes inside solids!

When x-rays shine onto solid materials or large molecules, an electron is pushed away from its original place near the nucleus of the atom, leaving a hole...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

“Lasers in Composites Symposium” in Aachen – from Science to Application

19.09.2017 | Event News

I-ESA 2018 – Call for Papers

12.09.2017 | Event News

EMBO at Basel Life, a new conference on current and emerging life science research

06.09.2017 | Event News

 
Latest News

Fraunhofer ISE Pushes World Record for Multicrystalline Silicon Solar Cells to 22.3 Percent

25.09.2017 | Power and Electrical Engineering

Usher syndrome: Gene therapy restores hearing and balance

25.09.2017 | Health and Medicine

An international team of physicists a coherent amplification effect in laser excited dielectrics

25.09.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>