Surface Modification of Silica-Supported Supraparticles to Control Their Optical Properties and Mobility in Electric Fields.

Supraparticles, which are spherical assemblies of colloidal particles, have great potential as photonic pigments. Specifically, they have potential as electronic ink particles for switchable display pixels due to their vivid and bright color. However, supraparticles often have low stability, which limits postassembly modification and their mobility in electric fields. In this work, we create robust supraparticles supported by silica via bulk emulsification. The shrinking rate of the droplets was controlled via osmosis to balance the rate of particle assembly, silica formation, and emulsion stability. The silica-supported supraparticles exhibit high order, reflectivity, and suspension stability. Their stability was exploited to modify the surface of the supraparticles with polydopamine (PDA) as the absorbing material to improve saturation. Coating entire supraparticles with PDA yielded similar color saturation compared to supraparticles created using PDA-coated building blocks. Additionally, the supraparticles' PDA surfaces were further functionalized using polyethylenimine to showcase the possibility of controlling the supraparticles' surface charge after self-assembly. Finally, the silica-supported supraparticles were moved electrophoretically, which paves the way for these photonic pigments to be used in applications such as reflective electronic ink.