Tunable Structural Coloration in Eccentric Water-in-Oil-in-Water Droplets

Structural colors show diverse advantages such as faderesistance,eco-friendliness, iridescence, and high saturation in comparison withchemical pigments. In this paper, we show tunable structural colorationin colorless water-in-oil-in-water double emulsion droplets via totalinternal reflection and interference at the microscale concave interfaces.Through experimental work and simulations, we demonstrate that theshell thickness and the eccentricity of the core-shell structuresare key to the successful formation of iridescent structural colors.Only eccentric thin-shell water-in-oil-in-water droplets show structuralcolors. Importantly, structural colors based on water-oil interfacesare readily responsive to a variety of environmental stimuli, suchas osmotic pressure, temperature, magnetic fields, and light composition.This work highlights an alternative structural coloration that expandsthe applications of droplet-based structural colors to aqueous systems.

Automated summary

Tunable structural coloration can be achieved in colorless water-in-oil-in-water double emulsion droplets through total internal reflection and interference at microscale concave interfaces. The shell thickness and eccentricity of the core-shell structures are found to be critical for the formation of iridescent structural colors. Only eccentric thin-shell water-in-oil-in-water droplets exhibit structural colors. Importantly, structural colors based on water-oil interfaces are highly responsive to various environmental stimuli including osmotic pressure, temperature, magnetic fields, and light composition. This work expands the applications of droplet-based structural colors to aqueous systems.