Therefore, additional steps aiming to tailor the interfaces on each hierarchical level were applied. On the 1st HL, the organic functionalization of the inorganic cores allows for further adjustment of the SC properties. Different suitable possibilities have been developed to tailor the interparticle cohesion. Herein, NC-interfacing organic ligands were crosslinked before embedding the SPs into the epoxy matrix via an annealing step under inert atmo-sphere, which substantially increases the robustness of the SC-materials. During this step, a radical oxidative polymerization catalyzed by the magnetite surface takes place leading to the formation of new covalent bonds between adjacent aliphatic chains (Fig. ). This crosslinking step proceeds under N 2 , at 325 °C for 0.3 h. Since the crosslinking reaction is accompanied by partial organic degradation, the SPs experience a weight loss of ca. 5.0 wt% (Fig. ) after annealing, which ultimately further increases the (inorganic) NC content in the final composite material up to 80.6 ± 1.9 wt%. This is a remarkably high value for the inorganic content of the composites, considering the high surface to volume ratio of the primary NCs and the fact that each hierarchical level adds further organic content to the system. The crosslinked supraparticles (xSPs) maintain the same periodic nanostructure as the self-assembled SPs, as can be seen in Fig. , but with slightly smaller superlattice constants -and therefore shorter interparticle distances, D IP , (Fig. ) down to 0.7 ± 0.1 nm.