Bioinspired Self-Assembly of Hollow Nanoparticles*

Structural colors, produced by interaction of light with nanostructures, have garnered significant interest among researchers because of their potential to replace toxic pigments and developing inks that do not fade upon exposure to light. The non-iridescent structural colors in birds are produced by combinations of keratin, melanin and air. This strategy has inspired some intriguing mimics for producing structural colors using self-assembly of polydopamine (PDA) nanoparticles, a synthetic analogue of melanin. Even though melanin is necessary for producing saturated colors, excess melanin content can lead to loss in brightness. In my presentation, I will discuss our strategy to create core-shell and hollow nanoparticles of various shell thicknesses using polystyrene (PS) nanoparticle template and coating it with PDA, providing a very high refractive index contrast. The PS core than can be dissolved away to produce saturated colors. We will present the reflectance data and our optical simulation results to explain the changes in colors between the core-shell and hollow nanoparticles. Understanding the physics of color generation would benefit a wide variety of applications including paints, coatings, and cosmetics.