further tunability by adjusting the microstructure of the foam through material processing. Complex parts with variable properties could then be made using multiple nozzles placing different foams in different locations. This could also be done, in principle, with a single nozzle, by making the foam on the fly, with whatever properties might be needed in the next section to be printed in a continuously variable manner.
This provides three degrees of freedom, that can be used to establish the characteristics of a given region, those being: the structure of the foam, the printed unit cell size and shape, and the stiffness (or conductivity or porosity) of the foam being applied. Each of these knobs significantly affects the property of interest, and when employed together may be used to significantly expand the range of attainable material performance.
After the material is laid down, it is solidified by means of a high-temperature sintering process, (approximately 1500˚C) which fuses together the ceramic particles. Muth was careful to point out that while the approach was demonstrated with ceramics, there is no reason why the same approach wouldn’t work with polymers or metals, either.
The foam is produced through a particle stabilization process. It’s similar to making a meringue. The surface energy of the particles is tuned so that they want to spontaneously attach to a liquid-air interface. Once air is introduced via a whisk, the mixture turns into a foam. This is accomplished by attaching certain molecules to the particles to achieve the desired degree of hydrophobicity.
The length scale of the elements produced are as follows: the particles start at~100 nanometers, the bubbles are ~10-100 microns. Filaments come out of the nozzle at ~0.5-1 mm, and the structures are on the order of ~10-100mm.