Dong Lin
Abstract
To realize this goal, we developed a novel 3D printing technique, as illustrated in , by integrating 3D printing ice and freeze casting to print GA. Different from other 3D printing processes where the materials are heated up or extruded out at room temperature, our 3D printing technique, illustrated in a, rapidly freezes the water based GO suspension and selectively solidifi es the aqueous droplets into ice crystal on a cold sink (−25 °C), well below water's freezing point. Therefore, the water, shown in b, and low viscous Newtonian GO suspension, shown in c, can be printed by drop-on-demand mode, where the material is ejected drop by drop only if needed. The dilute pure aqueous GO suspension, with low GO density (1 mg mL −1 ), offers lower density and larger surface area for printed GA when compared with the-state-of-the-art printing technique for GA. In traditional continuous deposition based 3D printing, physical properties of printed parts are negatively infl uenced by insuffi cient bonding at the interface driven by intermolecular diffusion and the undesirable voids between the adjacent fi laments. In our printing process, when liquid solution is deposited on top of previously frozen material, the not-yet-frozen material melts the already frozen surface. These two materials are mixed and refrozen together under low temperature (−25 °C). Because the remelted aqueous material possesses low viscosity, the voids between layers are instantly fi lled by the liquid material under surface tension and gravity. Since the deposited materials freeze and fi rmly bond together with the previous layer via hydrogen bond, high structural integrity of the fi nal assembled GA can be achieved, as further confi rmed in the mechanical test section. The pure water serves as a supporting structure to build complex architecture with overhang features. As shown in , the post processing includes immersion of 3D printed architectures in liquid nitrogen, freeze drying to remove the water, and thermal annealing to achieve a 3D printed ultralight GA truss. As shown in g, 2.5 D (left) and truly 3D truss (right), GO aerogel structure can be printed. We also printed grid GO aerogel structures with various wall thicknesses, decreasing from left to right in h, in order to demonstrate the printing ability. -c (Supporting Information) illustrates more 3D printed GO aerogels on catkin and -f (Supporting Information) shows various design and structures with different wall thicknesses. Compared to the continuous printing mode, the drop-on-demand technique achieves higher precision and is easier to extend for printing multiple materials with multinozzles, paving the way for fabrication of multifunctional aerogel materials in myriad applications.
Key takeaways
- The chemical composition of 3D printed GA was characterized, as shown in Figure 3 .
- The electrical conductivity against density for graphene composites, [ 19,20 ] bulk GA, [ 21 ] and printed GA are illustrated in Figure 4 d. The 3D printed GAs exhibit high electrical conductivities, ranging from 2.2 to 15.4 S m −1 as the densities increase from 0.5 to 10 mg cm −3 .
- More details of comparison between printed GA and other aerogel can be seen in Table S1 (Supporting Information).
- This technique enables tailoring the microstructure and macrostructure of printed GA. Based on our knowledge, we fi rst report the 3D printed GA truss architecture with overhang structures.
- After printing, the 3D printed GO ice lattice was immersed into liquid nitrogen to implement the critical freezing process for 30 min and then .
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