Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:


Surface wetting – tracking down the causes of polar hydrophobicity


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: - Publication in J. Am. Chem. Soc., 2016, 138 (12), pp 4018–4028, DOI: 10.1021/jacs.5b04073 - Fraunhofer Institute for Mechanics of Materials IWM

Katharina Hien | Fraunhofer-Institut für Werkstoffmechanik IWM

More articles from Information Technology:

nachricht Fraunhofer FIT joins Facebook's Telecom Infra Project
25.10.2016 | Fraunhofer-Institut für Angewandte Informationstechnik FIT

nachricht Stanford researchers create new special-purpose computer that may someday save us billions
21.10.2016 | Stanford University

All articles from Information Technology >>>

The most recent press releases about innovation >>>

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

Im Focus: Etching Microstructures with Lasers

Ultrafast lasers have introduced new possibilities in engraving ultrafine structures, and scientists are now also investigating how to use them to etch microstructures into thin glass. There are possible applications in analytics (lab on a chip) and especially in electronics and the consumer sector, where great interest has been shown.

This new method was born of a surprising phenomenon: irradiating glass in a particular way with an ultrafast laser has the effect of making the glass up to a...

Im Focus: Light-driven atomic rotations excite magnetic waves

Terahertz excitation of selected crystal vibrations leads to an effective magnetic field that drives coherent spin motion

Controlling functional properties by light is one of the grand goals in modern condensed matter physics and materials science. A new study now demonstrates how...

Im Focus: New 3-D wiring technique brings scalable quantum computers closer to reality

Researchers from the Institute for Quantum Computing (IQC) at the University of Waterloo led the development of a new extensible wiring technique capable of controlling superconducting quantum bits, representing a significant step towards to the realization of a scalable quantum computer.

"The quantum socket is a wiring method that uses three-dimensional wires based on spring-loaded pins to address individual qubits," said Jeremy Béjanin, a PhD...

Im Focus: Scientists develop a semiconductor nanocomposite material that moves in response to light

In a paper in Scientific Reports, a research team at Worcester Polytechnic Institute describes a novel light-activated phenomenon that could become the basis for applications as diverse as microscopic robotic grippers and more efficient solar cells.

A research team at Worcester Polytechnic Institute (WPI) has developed a revolutionary, light-activated semiconductor nanocomposite material that can be used...

Im Focus: Diamonds aren't forever: Sandia, Harvard team create first quantum computer bridge

By forcefully embedding two silicon atoms in a diamond matrix, Sandia researchers have demonstrated for the first time on a single chip all the components needed to create a quantum bridge to link quantum computers together.

"People have already built small quantum computers," says Sandia researcher Ryan Camacho. "Maybe the first useful one won't be a single giant quantum computer...

All Focus news of the innovation-report >>>



Event News

#IC2S2: When Social Science meets Computer Science - GESIS will host the IC2S2 conference 2017

14.10.2016 | Event News

Agricultural Trade Developments and Potentials in Central Asia and the South Caucasus

14.10.2016 | Event News

World Health Summit – Day Three: A Call to Action

12.10.2016 | Event News

Latest News

How nanoscience will improve our health and lives in the coming years

27.10.2016 | Materials Sciences

OU-led team discovers rare, newborn tri-star system using ALMA

27.10.2016 | Physics and Astronomy

'Neighbor maps' reveal the genome's 3-D shape

27.10.2016 | Life Sciences

More VideoLinks >>>