It's not always ice all the way through. Its surface can be coated in a film of liquid atoms with its thickness usually only a few nanometers.
Ice cubes can stick together in the freezer because of the pre melting process.
In addition to ice, we've observed a premelted surface layer in a wide range of materials, where the atoms inside are arranged in a nicely ordered lattice.
Scientists have seen surface melting in glass for the first time.
On the atomic scale, glass and ice are very different from one another. Amorphous solid, also known as glass, is what we call it when it's nice and tidy. It's atoms are just like you'd expect them to be in a liquid.
It is more difficult to see a film on the surface of glass because of this.
The detection of this filmy liquid layer is usually made by scattering neutrons or X-rays.
The surface is not melting as much as the solid ice. It's all a mess in glass and scattering wouldn't be useful.
The University of Konstanz in Germany has two physicists. They created a suspension of glass spheres in a liquid that behaves like the atoms in atomic glass.
The spheres are 10,000 times larger than atoms and can be seen under a microscope.
The particles at the surface were moving faster than the particles in the bulk glass beneath it.
It was not a surprise. The surface particles have more room to move because the bulk glass's density is higher. The particles move more quickly than the bulk glass even when they reach bulk glass densities.
The researchers wrote in their paper that their results show that surface melting of glasses is qualitatively different from crystals.
"This layer contains clusters of highly mobile particles which are formed at the surface and which colonize deep into the material by several tens of particle diameter and beyond the region where the particle density saturates."
Since surface melting alters the properties of a material's surface, the results offer a better understanding of glass, which is extremely useful across a range of applications.
High surface mobility could explain why thin films have higher ionic conductivity than thick films. These films act as ionic conductors and will be used in batteries.
Scientists will be able to find new ways to use this property if they understand what causes it and how it can be stimulated.
The research was published in a journal.
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