AsianScientist (Nov. 11, 2015) – In a paper published in Angewandte Chemie International Edition, a group of scientists has reported the generation of soft matter that changes color as the temperature varies.
Chameleon skin and some types of fish skin are regarded as prototypes of structurally colored materials that change their color appearance upon external stimuli. These stimuli can be light and dark transitions or other environmental factors. In artificial structurally colored soft materials, temperature variation can be the stimulus, causing the swelling or shrinking of the structure.
Associate Professor Yukikazu Takeoka and his colleagues from Nagoya University have created a hydrogel templated on amorphous arrays of fine silica particles that, like chameleon skin upon excitement, promptly responds to temperature variations by volume changes.
“The fast response is attributed to the interconnecting pore structure generated from the colloidal amorphous array,” the scientists explained.
However, incoherent scattering in these novel thermosensitive hydrogels prevents the structural colors from being visible, making their surface appearing just white. Therefore, the scientists added a very small amount of carbon black to their amorphous colloidal silica arrays.
“As a result, we can observe structural colors from colloidal amorphous arrays due to the enhancement of the structural color saturation by reducing the incoherent wavelength-independent scattering of light across the entire visible region,” they explained.
The carbon black doping was also preserved in the thermosensitive hydrogels prepared from the colloidal silica arrays.
The scientists observe, “The hydrogels with a carbon black content of less then 0.1 percent could display brilliant structural colors, which change with their volume for different water temperatures.”
As the colors vary from dusty red to green and blue, the novel carbon black doped hydrogels can be seen as a new type of tunable structurally colored soft material.
However, the most important feature of these structurally colored soft materials, which makes them applicable even to full-color displays, is the independence of the structural color from the measurement angle. The angular dependence has hampered their use in displays, although tunable colors would be highly advantageous as no filter is needed.
Therefore, the authors suggest that their novel thermosensitive porous hydrogels could be used even in reflective full-color displays and sensor systems with wide viewing angles, as well as biochemical sensing technologies and electronic paper.
The article can be found at: Ohtsuka et al. (2015) Thermally Tunable Hydrogels Displaying Angle-Independent Structural Colors.
Source: Angewandte Chemie.
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