This eight centimeter tall Christmas tree is made entirely of ice. A research team led by Menno Demmenie from the University of Amsterdam produced it in just 26 minutes using a 3D printer. However, they did not use any support or framework material or cooling equipment, just liquid water and a low-pressure chamber with a vacuum.
The physical principle that makes this ice printing technique possible for Christmas decorations is called evaporative cooling: water molecules evaporate rapidly when they are in a room with low air pressure or in a vacuum. However, for this phase change from liquid to gaseous, the water molecules need energy, which they extract from the remaining water. This is then continually cooled and eventually reaches temperatures below freezing.
The supercooled liquid water can then be sprayed onto a surface in an ultra-fine jet. This creates spontaneous crystallization nuclei and the sprayed water freezes almost immediately. In this way, you can practice 3D printing with water and form any ice sculpture, layer by layer, for example this Christmas tree. The only disadvantage: As soon as the vacuum pump is switched off, the ice tree quickly melts again and turns back into liquid water.
Mammals also use the same principle of evaporative cooling when they sweat to regulate their body temperature, as Demmenie’s team explains. Their ice printing technique can now also be used for practical things, such as forming self-dissolving frameworks for tissue or microfluids out of ice. The technology could even be used on Mars to produce ice structures there – it is cold there, there is water and the atmosphere is thin enough to enable evaporative cooling without an extra pressure chamber. In combination with sand, a kind of permafrost soil could also be printed.