The micro-building material of the future: aerogel

Aerogel is an excellent thermal insulator. So far, however, it has mainly been used on a large scale, for example in environmental technology, in physical experiments or in industrial catalysis. Empa researchers have now succeeded in making aerogels accessible to microelectronics and precision engineering: An article in the latest issue of the scientific journal "Nature" shows how 3D-printed parts made of silica aerogels and silica composite materials can be manufactured with high precision. This opens up numerous new application possibilities in the high-tech industry, for example in microelectronics, robotics, biotechnology and sensor technology.

Behind the simple headline "Additive manufacturing of silica aerogels" - the article appeared in the trade journal "Nature" on August 20 - lies a groundbreaking development. Silica aerogels are lightweight, porous foams that provide excellent thermal insulation. In practice, they are known for their brittle behavior, which is why they are usually reinforced on a large scale with fibers or with organic or biopolymers. Due to their brittle fracture behavior, it is also not possible to cut or mill small pieces out of an aerogel block. It is also not possible to solidify aerogels in miniaturized molds reliably - which leads to high scrap rates. This is why aerogels have hardly been usable on a small scale until now.

Stable, well-formed microstructures

The Empa team around Shanyu Zhao, Gilberto Siqueira, Wim Malfait and Matthias Koebel have now succeeded in producing stable, well-shaped microstructures from silica aerogel using a 3D printer. The printed structures can be as thin as a tenth of a millimeter. The thermal conductivity of the silica aerogel is just under 16 mW/(m*K) - only half that of polystyrene, and even significantly less than that of an unmoving layer of air at 26 mW/(m*K). At the same time, the new 3D-printed silica aerogel has even better mechanical properties and can even be drilled and milled. This opens up completely new possibilities for post-processing of 3D-printed aerogel moldings.

With the method, which has since been patented, it is possible to precisely adjust the flow and solidification properties of the silica ink from which the aerogel is later produced, so that both self-supporting structures and wafer-thin membranes can be printed. As an example of overhanging structures, the researchers printed leaves and blossoms of a lotus flower. The test object floats on the water surface due to the hydrophobic properties and low density of the silica aerogel - just like its natural model. The new technology also makes it possible for the first time to print complex 3D multi-material microstructures.

Insulation materials for microtechnology and medicine

With such structures it is now comparatively trivial to thermally insulate even the smallest electronic components from each other. The researchers have already been able to demonstrate the thermal shielding of a temperature-sensitive component and the thermal management of a local "hot spot" in an impressive way. Another possible application is the shielding of heat sources inside medical implants, which should not exceed a surface temperature of 37 degrees in order to protect body tissue.

A functional aerogel membrane

3D printing makes it possible to produce multilayer/multi-material combinations much more reliably and reproducibly. New types of aerogel fine structures become feasible and open up new technical solutions, as a second application example shows: Using a printed aerogel membrane, the researchers constructed a "thermomolecular" gas pump. This permeation pump manages completely without moving parts and is also known in technical jargon as the Knudsen pump, named after the Danish physicist Martin Knudsen. The principle of operation is based on the restricted gas transport in a network of nanoscale pores or one-dimensional channels whose walls are hot at one end and cold at the other. The team manufactured such a pump from aerogel that was doped with black manganese oxide nanoparticles on one side. When this pump is placed in the light, it becomes warm on the dark side and starts pumping gases or solvent vapors from the cold to the warm side.

Exhaust air purification without moving parts

These applications demonstrate the power of 3D printing in a compelling way: 3D printing turns the high-performance material aerogel into a building material for functional membranes that can be quickly modified for a wide range of applications. The Knudsen pump, which is powered solely by sunlight, can do more than just pump.

Original article: Nature - Additive manufacturing of silica aerogels

Source: Chemie.de - Aerogel: Der Mikro-Baustoff der Zukunft
Image source: Nature - Additive manufacturing of silica aerogels (Original article)