Preparation of structural colors assembled by SiO2@PDA microspheres to achieve inhibition of coffee-ring effect by multilayer coating on paper substrate

Structural colors composed of silica (SiO 2 ) microspheres have attracted the attention of researchers due to their environmental sustainability, vivid colors, and dynamic adjustability. However, the coffee-ring effect is a common phenomenon that occurs during the evaporation of droplets on the paper substrate and can notably affect color performance. In this study, dopamine (DA) was employed for the oxidative self-polymerization of the surface of SiO 2 microspheres to Polydopamine (PDA), resulting in SiO 2 @PDA microspheres with different absorbance. By multilayer coating, SiO 2 @PDA induced by evaporation at room temperature was assembled into a disordered structure, facilitating bright amorphous photonic crystals (APCs) on handmade paper. The addition of the sizing agent enhanced the adhesion strength and durability of the coating. Thus, the negative impact of coffee-ring of structural color is not only reduced by multilayer coating, but it is also simple to operate and vivid colors can be constructed on handmade paper, which is conducive to replacing traditional chemically dyed paper and achieving industrial-scale production.