3D Printing of Ultrahigh Filler Content Composites Enabled by Granular Hydrogels

Ultrahigh filler content composites have exhibited distinctive properties in various areas, such as structural materials, electrical insulation, thermal management, and energy storage devices. However, manufacturing 3D composites with ultrahigh filler content is challenging because excessive fillers have compromised the processing flowability of the composite. Here, using hollow glass microspheres (HGMs) as an example filler, a 3D printing strategy for fabricating particulate composites with ultrahigh HGM content (up to 99.2 wt.%) is reported. By incorporating the highly swollen granular hydrogel as the shear sliding phase between HGMs, the probability of clogging during extrusion of the composite ink with ultrahigh HGM content is substantially reduced. A quantitative phase diagram is developed to optimally choose the ink compositions with the maximum HGM content, as well as printing parameters. The resulting composite with ultrahigh HGM content shows ceramic-foam-like brittle fracture behavior, high wave-transparent properties (0.996), and low thermal conductivity (0.045 W m^-1 K^-1). Further, a thermal shield with high HGM content on a microcircuit board to validate the localized thermal protection is fabricated. It is believed that incorporating hydrogel matrix into the printing ink will unlock the capabilities of 3D printed ultrahigh filler content composites in creating more intricate structures with advanced functionalities.