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 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.
Prof. Daniel Bonn
1090 GL Amsterdam
phone: +31 (0)205255887
Prof. Mischa Bonn
Max Planck Institute for Polymer Research
phone: +49 (0)6131 379 161
Link to publication:
Link to Max Planck Institute for Polymer Research:
Dr. Christian Schneider | Max-Planck-Institut für Polymerforschung
From foam to bone: Plant cellulose can pave the way for healthy bone implants
19.03.2019 | University of British Columbia
Additive printing processes for flexible touchscreens: increased materials and cost efficiency
19.03.2019 | INM - Leibniz-Institut für Neue Materialien gGmbH
DESY and MPSD scientists create high-order harmonics from solids with controlled polarization states, taking advantage of both crystal symmetry and attosecond electronic dynamics. The newly demonstrated technique might find intriguing applications in petahertz electronics and for spectroscopic studies of novel quantum materials.
The nonlinear process of high-order harmonic generation (HHG) in gases is one of the cornerstones of attosecond science (an attosecond is a billionth of a...
Nano- and microtechnology are promising candidates not only for medical applications such as drug delivery but also for the creation of little robots or flexible integrated sensors. Scientists from the Max Planck Institute for Polymer Research (MPI-P) have created magnetic microparticles, with a newly developed method, that could pave the way for building micro-motors or guiding drugs in the human body to a target, like a tumor. The preparation of such structures as well as their remote-control can be regulated using magnetic fields and therefore can find application in an array of domains.
The magnetic properties of a material control how this material responds to the presence of a magnetic field. Iron oxide is the main component of rust but also...
Due to the special arrangement of its molecules, a new coating made of corn starch is able to repair small scratches by itself through heat: The cross-linking via ring-shaped molecules makes the material mobile, so that it compensates for the scratches and these disappear again.
Superficial micro-scratches on the car body or on other high-gloss surfaces are harmless, but annoying. Especially in the luxury segment such surfaces are...
The Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI) at the Large Binocular Telescope (LBT) in Arizona released its first image of the surface magnetic field of another star. In a paper in the European journal Astronomy & Astrophysics, the PEPSI team presents a Zeeman- Doppler-Image of the surface of the magnetically active star II Pegasi.
A special technique allows astronomers to resolve the surfaces of faraway stars. Those are otherwise only seen as point sources, even in the largest telescopes...
Researchers at Chalmers University of Technology and the University of Gothenburg, Sweden, have proposed a way to create a completely new source of radiation. Ultra-intense light pulses consist of the motion of a single wave and can be described as a tsunami of light. The strong wave can be used to study interactions between matter and light in a unique way. Their research is now published in the scientific journal Physical Review Letters.
"This source of radiation lets us look at reality through a new angle - it is like twisting a mirror and discovering something completely different," says...
11.03.2019 | Event News
01.03.2019 | Event News
28.02.2019 | Event News
22.03.2019 | Life Sciences
22.03.2019 | Life Sciences
22.03.2019 | Information Technology