Structurally Colored Inks from Synthetic Melanin-Based Crosslinked Supraparticles

Structurally colored supraparticles, formed from dispersed nanoparticle building blocks through self-assembly, have tremendous potential for applications in displays, coatings, paints, inks, and cosmetics. Mechanical stability and solvent compatibility of supraparticles is critical in these applications. Here, we describe the scalable synthesis of supraparticles via the assembly of nanoparticles composed of synthetic melanin cores with silica shells (SM@SiO2 NPs) using a vortex-assisted reverse emulsion method. We use a hydrogen-bond driven crosslinking strategy employing polyethylene glycol to lock the SM@SiO2 NP building blocks together. This approach yields multicolor photonic supraparticles stable both in organic and aqueous solvents and in the dry state. Supraparticles crosslinked via 4-arm PEG2k withstand at least a 10-fold increase in compressive force when compared to noncrosslinked versions. Capitalizing on the enhanced stability of crosslinked supraparticles, we directly blend them with painting media and apply them as inks.