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.