Tag Archives: Michael Faraday

How does ice melt? Layer by layer!

A Dec. 12, 2016 news item on ScienceDaily announces the answer to a problem scientists have been investigating for over a century but first, here are the questions,

We all know that water melts at 0°C. However, 150 years ago the famous physicist Michael Faraday discovered that at the surface of frozen ice, well below 0°C, a thin film of liquid-like water is present. This thin film makes ice slippery and is crucial for the motion of glaciers.

Since Faraday’s discovery, the properties of this water-like layer have been the research topic of scientists all over the world, which has entailed considerable controversy: at what temperature does the surface become liquid-like? How does the thickness of the layer dependent on temperature? How does the thickness of the layer increases with temperature? Continuously? Stepwise? Experiments to date have generally shown a very thin layer, which continuously grows in thickness up to 45 nm right below the bulk melting point at 0°C. This also illustrates why it has been so challenging to study this layer of liquid-like water on ice: 45 nm is about 1/1000th part of a human hair and is not discernible by eye.

Scientists of the Max Planck Institute for Polymer Research (MPI-P), in a collaboration with researchers from the Netherlands, the USA and Japan, have succeeded to study the properties of this quasi-liquid layer on ice at the molecular level using advanced surface-specific spectroscopy and computer simulations. The results are published in the latest edition of the scientific journal Proceedings of the National Academy of Science (PNAS).

Caption: Ice melts as described in the text layer by layer. Credit: © MPIP

A Dec. 12, 2016 Max Planck Institute for Polymer Research press release (also on EurekAlert), which originated the news item, goes on to answer the questions,

The team of scientists around Ellen Backus, group leader at MPI-P, investigated how the thin liquid layer is formed on ice, how it grows with increasing temperature, and if it is distinguishable from normal liquid water. These studies required well-defined ice crystal surfaces. Therefore much effort was put into creating ~10 cm large single crystals of ice, which could be cut in such a way that the surface structure was precisely known. To investigate whether the surface was solid or liquid, the team made use of the fact that water molecules in the liquid have a weaker interaction with each other compared to water molecules in ice. Using their interfacial spectroscopy, combined with the controlled heating of the ice crystal, the researchers were able to quantify the change in the interaction between water molecules directly at the interface between ice and air.

The experimental results, combined with the simulations, showed that the first molecular layer at the ice surface has already molten at temperatures as low as -38° C (235 K), the lowest temperature the researchers could experimentally investigate. Increasing the temperature to -16° C (257 K), the second layer becomes liquid. Contrary to popular belief, the surface melting of ice is not a continuous process, but occurs in a discontinuous, layer-by-layer fashion.

“A further important question for us was, whether one could distinguish between the properties of the quasi-liquid layer and those of normal water” says Mischa Bonn, co-author of the paper and director at the MPI-P. And indeed, the quasi-liquid layer at -4° C (269 K) shows a different spectroscopic response than supercooled water at the same temperature; in the quasi-liquid layer, the water molecules seem to interact more strongly than in liquid water.

The results are not only important for a fundamental understanding of ice, but also for climate science, where much research takes place on catalytic reactions on ice surfaces, for which the understanding of the ice surface structure is crucial.

Here’s a link to and a citation for the paper,

Experimental and theoretical evidence for bilayer-by-bilayer surface melting of crystalline ice by M. Alejandra Sánchez, Tanja Kling, Tatsuya Ishiyama, Marc-Jan van Zadel, Patrick J. Bisson, Markus Mezger, Mara N. Jochum, Jenée D. Cyran, Wilbert J. Smit, Huib J. Bakker, Mary Jane Shultz, Akihiro Morita, Davide Donadio, Yuki Nagata, Mischa Bonn, and Ellen H. G. Backus. Proceedings of the National Academy of Science, 2016 DOI: 10.1073/pnas.1612893114 Published online before print December 12, 2016

This paper appears to be open access.

Scientific Christmases in the 19th century

Rupert Cole has written about how an interest in science revived the celebration of Christmas in early 19th century Britain in a Dec. 14, 2012 posting on the Guardian science blogs (Note: I have removed links),

In the first few decades of the 19th century, Christmas was a rather rarefied tradition, kept alive by the nostalgia of poets and antiquarians. Romantically inclined writers such as William B Sandys and Thomas Kibble Hervey feared for the end of “Old Christmas” – the age, they lamented, had become too philosophic, too utilitarian and too refined for boozy wassail bowls, feudal feasts and Lords of Misrule.

On the eve of the Victorian era, however, Christmas underwent a transformation, becoming a popular festival once again – reinvented for the modern age. And as science was reaching unprecedented levels of popularity around the same time, the two cultures overlapped.

Publications like The Illustrated London News and The Leisure Hour printed Christmas essays, stories and poems that celebrated scientific progress. Christmas books and annuals included experiments for children. Newspapers ran adverts for “scientific Christmas presents” and articles describing “Christmas scientific recreations”.

Here’s a great description of a scientific pantomime,

By 1848, festive science was all the rage. That year, the Victoria Theatre staged one of the most sensational and oversubscribed pantomimes of the decade. E L Blanchard’s Land of Light, or Harlequin Gas and the Four Elements made “Science” the personified hero.

The opening scene takes place in a “goblin coal mine” 5,000 miles beneath the surface of the Earth, where an unhappy troop of fairies bemoan their banishment from the science-enamoured society above. The character Science arrives, challenging the fairies to a contest of traditional panto magic.

Science steals the show by combusting a slab of coal. The stage directions at this point indicate that the player Gas appears from the coal “with flame upon his head”. And to further perturb even the most hardened health-and-safety enthusiast, the scene’s magical finale consists of a “magnificent temple” of artificial light, fuelled by a selection of intensely bright (and extremely explosive) gases in use at the time – Budelight, limelight and camphine.

Pantomime became an exclusively Christmas tradition during the Victorian era, but it was much more politically edgy, witty and spectacular than the best of today’s efforts – which tend to rely on the fame and acting abilities of soap stars.

Cole goes on to describe extraordinary science Christmas-themed exhibitions and mentions that even Prince Albert (Queen Victoria’s hubby) made a point of attending one of the myriad science-themed Christmas events of the day.

Prince Albert and the ‘royal children’ attend Michael Faraday’s 1855 Christmas Lecture, ‘The Distinctive Properties of the Common Metals’. Image: Illustrated London News archive (accessed from http://www.guardian.co.uk/science/blog/2012/dec/14/science-christmas-victorian-romance]

There’s more detail and more illustrations in the Cole’s piece which ends with this,

The first of three Royal Institution Christmas Lectures, Air: The Elixir of Life, will be broadcast on BBC Four on 26 December