From ice skating, it has been known for a long time that a thin liquid film forms on ice surfaces. This, along with other causes, is responsible for ice slipperiness. Scientists at the Max Planck Institute for Polymer Research have now investigated a related effect at interfaces between ice and porous clay minerals. Such interfaces are found in nature for example in permafrost. The results may help to better understand changes in frozen soils as temperatures rise.
For ice, so-called "surface melting" was postulated as early as the 19th century by Michael Faraday: Already below the actual melting point, i.e. 0 °C, a thin liquid film forms on the free surface because oft he interface between ice and air. Scientists led by Markus Mezger, group leader at the Max Planck Institute for Polymer Research (department of Hans-Jürgen Butt) and professor at the University of Vienna, have now studied this phenomenon in more detail at interfaces between ice and clay minerals.
In nature, this effect is particularly interesting in permafrost soils - i.e. soils that are permanently frozen. About a quarter of the land area in the northern hemisphere is covered by permafrost. These are composed of a mixture of ice and other materials. Microscopically thin platelets were formed over geological time by the weathering of clay minerals. Similar to a sponge, a lot of water can enter the narrow slit pores between the thin platelets, be stored there, and freeze. Therefore, there is a lot of contact area between ice and clay minerals. For every gram of clay mineral, there are about 10 square meters of surface area! This causes a comparatively high proportion of liquid water in the interfacially induced melt layer already below 0 °C.
Read more at Max Planck Institute for Polymer Research
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