Versatile Direct Writing of Aerogel-Based Sol-Gel Inks

Direct ink writing (DIW) of aerogels has great potential in designing novel three-dimensional (3D) multifunctional materials with hierarchical structures ranging from the nanoscale to the macroscopic scale. In this paper, pure aerogels composed of inorganics, strongly cross-linking organics, and weakly cross-linking organics were directly written via the precise control of the gelation degree without using any additives. The rheological properties of a resorcinol-formaldehyde aerogel-based sol-gel ink (marked as RA ink) were measured at different reaction times to determine the suitable printable range (G'_LVR: several 10³ Pa) that ensures its good print fidelity. In addition, the rheological evolution of the RA ink during the sol-gel process and under different shear stresses was studied. The correlation of relevant parameters was established according to the Hagen-Poiseuille model. Other typical aerogel-based sol-gel inks including a silica aerogel-based sol-gel ink (SA ink) and a polyimide aerogel-based sol-gel ink (PA ink) for DIW were also demonstrated. Finally, water evaporation experiments were carried out using a 3D-printed carbonized resorcinol-formaldehyde aerogel (CA) to further exhibit the potential applications of this novel technology in solar steam generation. The evaporation rate (1.57 kg m^-2 h^-1) and efficiency (88.38%) of 3D-printed CA were higher than those of bulk CA (1.21 kg m^-2 h^-1 and 69.82%). This paper systematically studies the control of DIW parameters for aerogel-based sol-gel inks and shows a potential application in high-efficiency 3D-printed evaporators.