Researchers at Kansas State University, University of Buffalo and the State University of New York have designed a new technique for 3D printing graphene aerogels with complex microstructures. The technique combines drop-on-demand 3D printing with freeze casting.
Aerogels are light and spongy materials that can be used as both thermal and optical insulators and can potentially be used as batteries and catalysts within electronic components. Recent years have brought about methods in which aerogels can be produced with certain 3D printers. The scientists have now developed a new 3D printing technique for producing graphene aerogels, which they hope will open up new uses for the material.The scientists wanted to develop a new method of 3D printing graphene aerogels, one which could accommodate more complex structures. Indeed, the technique that was developed developed eliminates the problems typically associated with 3D printed graphene aerogels, by incorporating freeze casting into the 3D printing process. Where the dominant method tends to be carried out at high or room temperatures, the team 3D printed the aerogels at -25°C. In such a cold environment, each layer froze after printing, allowing to build up an ice-supported graphene oxide structure. With each newly deposited layer of graphene oxide, the unfrozen material melted the frozen top layer. This allowed the layers to mix freely before refreezing in the cold environment, a process which improved the structural integrity of the 3D print by encouraging the formation of hydrogen bonds. A second printer nozzle filled with with only water was used to create ice supports for the structure.
The 3D printed graphene aerogel was finally freeze-dried in liquid nitrogen to get rid of all of the water deposited by the second printer nozzle, before being thermally reduced to graphene. The scientists were able to 3D print aerogels with densities ranging from 0.5 to 10mg/cm3, each with good electrical conductivity and high compressibility.