Visualization of the Assembly Behaviors of Gel Layer-Coated Melanin Particles at the Air/Water Interface via Structural Color

Surface-modified particles and microgels are known to adsorb at the air/water interface. This particle assembly behavior has been evaluated primarily under conditions in which all particles are adsorbed using a dilute dispersion. Herein, we visualized the adsorption/stabilization process of particle assemblies at the air/water interface in a concentrated dispersion based on structural coloration. Melanin particles were coated with a gel layer, and then aqueous dispersions were prepared and dried. Pristine melanin particle dispersions produced pronounced "coffee-ring" patterns with almost no particle deposition in the center. In contrast, the use of polymer gel-coated particles suppressed the coffee-ring effect and caused particle deposition in both the center of the pattern and around the periphery, indicating that the gel layer affected the assembly behavior. During the drying process, structural color analysis revealed stabilization at the air/water interface and differences in the size and motion of the domain. Furthermore, this gel-coated particle was shown to be effective for structural color coating with uniform visibility.