Abstract: Structural colors observed in nature have attracted considerable scientific interest and inspired the development of artificial coloring materials based on periodic nanostructures. Although numerous structural color materials have been proposed, reports on all-liquid systems, which can be incorporated into devices of arbitrary shapes, remain limited. We previously demonstrated that all-liquid emulsions composed of a long-chain amidoamine derivative (C18AA) and tetraoctylammonium bromide (TOAB) exhibit structural coloration within two temperature regions. For the formation of such coloring emulsions, the development of a stable interfacial layer of C18AA adsorbed at the toluene-water interface is crucial. However, it remains unclear whether other amphiphilic compounds can contribute to the formation of this interfacial layer. In this study, the effects of adding different amphiphilic compounds on the coloring behavior of C18AA emulsions was investigated, and their incorporation into the interfacial layer of C18AA was explored. Stearic acid, octadecylamine, and octadecanol did not considerably affect the coloring behavior. In contrast, C18AOH, in which the terminal amine group of C18AA is replaced by a hydroxyl group, could be incorporated into the C18AA interfacial layer. This insertion increased the toluene-water interfacial area, resulting in a blue shift of the observed color. Similar incorporation effects were observed for C16AOH and C14AOH, which have shorter alkyl chains. These findings can facilitate the color and thermal response tuning of all-liquid structural color emulsions based on interfacial engineering.
Fujiwara et al. (Thu,) studied this question.