Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

The Slipperiness of Ice Explained

09.05.2018

Everybody knows that sliding on ice or snow, is much easier than sliding on most other surfaces. But why is the ice surface slippery? This question has engaged scientists for more than a century and continues to be subject of debate. Researchers from AMOLF, the University of Amsterdam and the Max Planck Institute for Polymer Research (MPI-P) in Mainz, have now shown that the slipperiness of ice is a consequence of the ease with which the topmost water molecules can roll over the ice surface.

Winter sports such as skiing, speed skating, figure skating, and curling require the slippery surfaces of ice and snow. While the fact that the ice surface is slippery is widely acknowledged, it is far from being completely understood.


In the experiments, a steel ball slides over the ice surface which consists of rapidly tumbling mobile water molecules that are only loosely bounded to the underlying ice.

© Nagata/MPI-P

In 1886 John Joly, an Irish physicist, offered the first scientific explanation for low friction on ice; when an object - i.e. an ice skate - touches the ice surface the local contact pressure is so high that the ice melts thereby creating a liquid water layer that lubricates the sliding.

The current consensus is that although liquid water at the ice surface does reduce sliding friction on ice, this liquid water is not melted by pressure but by frictional heat produced during sliding.

A team of researchers led by brothers Prof. Daniel Bonn from the University of Amsterdam and Prof. Mischa Bonn from MPI-P, have now demonstrated that friction on ice is more complex than so far assumed.

Through macroscopic friction experiments at temperatures ranging from 0 °C to -100 °C the researchers show that - surprisingly - the ice surface transforms from an extremely slippery surface at typical winter sports temperatures, to a surface with high friction at -100 °C.

To investigate the origin of this temperature-dependent slipperiness, the researchers performed spectroscopic measurements of the state of water molecules at the surface, and compared these with molecular dynamics (MD) simulations.

This combination of experiment and theory reveals that two types of water molecules exist at the ice surface: water molecules that are stuck to the underlying ice (bound by three hydrogen bonds) and mobile water molecules that are bound by only two hydrogen bonds. These mobile water molecules continuously roll over the ice - like tiny spheres - powered by thermal vibrations.

As the temperature increases, the two species of surface molecules are interconverted: the number of mobile water molecules is increased at the expense of water molecules that are fixed to the ice surface. Remarkably, this temperature driven change in the mobility of the topmost water molecules at the ice surface perfectly matches the temperature-dependence of the measured friction force: the larger the mobility at the surface, the lower the friction and vice versa.

The researchers therefore conclude that - rather than a thin layer of liquid water on the ice - the high mobility of the surface water molecules is responsible for the slipperiness of ice.

Although the surface mobility continues to increase all the way up to 0 °C, this is not the ideal temperature for sliding on ice. The experiments show that the friction is in fact minimal at -7 °C; the exact same temperature is imposed at speed skating rinks.

The researchers show that at temperatures between -7 °C and 0 °C, sliding is more difficult because the ice becomes softer, causing the sliding object to dig deeper into the ice.

The results are published in the Journal of Physical Chemistry Letters.

Contact:
Prof. Daniel Bonn
Postbus 94485
1090 GL Amsterdam
eMail: d.bonn@uva.nl
phone: +31 (0)205255887

Prof. Mischa Bonn
Max Planck Institute for Polymer Research
Ackermannweg 10
D-55128 Mainz
eMail: bonn@mpip-mainz.mpg.de
phone: +49 (0)6131 379 161

Link to publication:
https://pubs.acs.org/doi/10.1021/acs.jpclett.8b01188

Link to Max Planck Institute for Polymer Research:
https://www.mpip-mainz.mpg.de/5334049/PM2018-12

Dr. Christian Schneider | Max-Planck-Institut für Polymerforschung

More articles from Materials Sciences:

nachricht In borophene, boundaries are no barrier
17.07.2018 | Rice University

nachricht Research finds new molecular structures in boron-based nanoclusters
13.07.2018 | Brown University

All articles from Materials Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: First evidence on the source of extragalactic particles

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...

Im Focus: Magnetic vortices: Two independent magnetic skyrmion phases discovered in a single material

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...

Im Focus: Breaking the bond: To take part or not?

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...

Im Focus: New 2D Spectroscopy Methods

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....

Im Focus: Chemical reactions in the light of ultrashort X-ray pulses from free-electron lasers

Ultra-short, high-intensity X-ray flashes open the door to the foundations of chemical reactions. Free-electron lasers generate these kinds of pulses, but there is a catch: the pulses vary in duration and energy. An international research team has now presented a solution: Using a ring of 16 detectors and a circularly polarized laser beam, they can determine both factors with attosecond accuracy.

Free-electron lasers (FELs) generate extremely short and intense X-ray flashes. Researchers can use these flashes to resolve structures with diameters on the...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Leading experts in Diabetes, Metabolism and Biomedical Engineering discuss Precision Medicine

13.07.2018 | Event News

Conference on Laser Polishing – LaP: Fine Tuning for Surfaces

12.07.2018 | Event News

11th European Wood-based Panel Symposium 2018: Meeting point for the wood-based materials industry

03.07.2018 | Event News

 
Latest News

Pollen taxi for bacteria

18.07.2018 | Life Sciences

Biological signalling processes in intelligent materials

18.07.2018 | Life Sciences

Study suggests buried Internet infrastructure at risk as sea levels rise

18.07.2018 | Information Technology

VideoLinks
Science & Research
Overview of more VideoLinks >>>