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.
Silica aerogels are light, porous foams that provide excellent thermal insulation.
In practice, they are also known for their brittle behaviour, which is why they are usually
reinforced with fibres or with organic or biopolymers for large-scale applications.
Due to their brittle fracture behaviour, it is also not possible to saw or mill small
pieces out of a larger aerogel block.
Directly solidifying the gel in miniaturised moulds is also not reliably - which results
in high scrap rates.
This is why aerogels have hardly been usable for small-scale applications.
The Empa researchers have now succeeded in producing stable, well-shaped microstructures
from silica aerogel by 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 only half that of polystyrene and even
significantly less than that of a non-moving layer of air.
At the same time, the novel printed silica aerogel has even better mechanical properties
and can even be drilled and milled.
This opens up completely new possibilities for the post-processing of 3D printed aerogel
mouldings.
With the method, for which a patent application has now been filed, 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.
With such structures it is now comparatively trivial to thermally insulate even the smallest
electronic components from each other.
The researchers were 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.
3D printing allows multilayer/multi-material combinations to be produced much more reliably
and reproducibly.
Novel aerogel fine structures become feasible and open up new technical solutions.
Using a printed aerogel membrane, the researchers constructed a "thermos-molecular" gas pump.
This permeation pump manages without any moving parts at all and is also known to the technical
community as a 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 of which the walls are hot at one end and cold at the
other.
The team built such a pump from aerogel, which was doped on one side with black manganese
oxide nanoparticles.
When this pump is placed under a light source, it becomes warm on the dark side and starts
to pump gases or solvent vapours.