Abstract
Stimuli-responsive structural color in nature has fascinated scientists, directing them to develop artificial coloration materials that adjust colors in response to external stimuli. Many stimuli-responsive structural color materials have been realized. However, only a few have reported on all-liquid-type materials, which have a particularly desirable feature because they impart their function to the device of any shape. We have previously reported the development of a consistent structural color within a narrow temperature range for all-liquid-type emulsions comprising a long-chain amidoamine derivative (C18AA) and tetraoctylammonium bromide (TOAB). In the present study, we demonstrate that introducing NaCl as an electrolyte affords a highly thermo-sensitive color-changing ability to the emulsions. The structural color of the emulsions can be controlled from red to blue by tuning the temperature. Furthermore, the C18AA and TOAB concentrations can independently regulate the color and coloring-temperature, respectively, realizing that the desired color can develop at a given temperature.
Highlights
Various plants and animals in nature exhibit an array of structural colors, such as the brilliant blue of the Morpho butterflies, iridescent green of some beetles, and iridescent eyelike pattern of peacock tail feathers, attracting the attention of many researchers.[1−5] artificial materials mimicking the structural colors in nature were developed and many efforts were devoted to constructing photonic materials with various nanostructures.[1−9] Generally, the fabrication methods are categorized into top-down and bottom-up strategies
We demonstrate that the addition of NaCl as an electrolyte to the C18AA and tetraoctylammonium bromide (TOAB) coloring emulsions generates two coloring-temperature regions and imparts an adjustable ability of structural color to the emulsions
Our previous paper reported that the C18AA and TOAB emulsions in water and toluene mixtures were transformed from the O/W to the W/O emulsion phase through a bicontinuous lamellar phase upon heating
Summary
Various plants and animals in nature exhibit an array of structural colors, such as the brilliant blue of the Morpho butterflies, iridescent green of some beetles, and iridescent eyelike pattern of peacock tail feathers, attracting the attention of many researchers.[1−5] artificial materials mimicking the structural colors in nature were developed and many efforts were devoted to constructing photonic materials with various nanostructures.[1−9] Generally, the fabrication methods are categorized into top-down and bottom-up strategies. Our previous study reported an all-liquid-type coloring emulsion comprising a long-chain amidoamine derivative (C18AA; Figure 1a) and tetraoctylammonium bromide narrow temperature range (approximately 3 °C) was controlled by adjusting the C18AA concentrations; the developed color was a constant tone in the whole coloringtemperature range and was incapable of tuning by the external stimuli. We demonstrate that the addition of NaCl as an electrolyte to the C18AA and TOAB coloring emulsions generates two coloring-temperature regions and imparts an adjustable ability of structural color to the emulsions. (TOAB; Figure 1b).[41] The emulsion demonstrated an oil-inwater (O/W) to water-in-oil (W/O) phase inversion upon heating, passing through a lamellar phase that developed the iridescent color. The coloration was attributed to the optical interference generated from the periodic lamellar structure composed of water, toluene, and surfactant layers of C18AA and TOAB (Figure 1c).
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