An Ice Christmas Tree: Fast Three-Dimensional Printing of Ice Structures via Evaporative Cooling in Vacuum

We demonstrate a novel approach to three-dimensional (3D) printing of freeform ice structures by exploiting evaporative cooling. A micrometer-sized water jet is used to 3D print inside a vacuum chamber. The reduced ambient pressure leads to rapid evaporation of the extruded water, extracting latent heat, and quickly cooling the water well below 0 {\deg}C. Once deposited, the water freezes almost instantaneously into stable ice structures. We demonstrate high-fidelity printing of complex geometries (Christmas trees, cones, vertical pillars, and free-standing zigzag structures) without cryogenic infrastructure, supporting materials, or external refrigeration. This approach directly visualizes fundamental thermodynamic principles -- latent heat, evaporative cooling, and pressure-dependent phase transitions -- while offering a relatively simple and scalable platform for ice-templated microfluidics and tissue engineering, or even extraterrestrial 3D printing.