AsianScientist (May 31, 2018) – Researchers from Tokyo Metropolitan University and Shimane University in Japan have created a transparent hybrid film that combines natural clay minerals and dyes into a material that changes color in response to environmental humidity. Their findings are published in Langmuir.
Combining dyes with a wide range of natural minerals like clathrates (clays) and zeolites (porous rock) is a promising strategy for creating hybrid materials that can interact with light—known as chromic materials. Chromic materials have potential applications in light harvesting, light emitting devices and sensors.
In the present study, a team led by Professor Takuya Fujimura from Shimane University and Professor Shinsuke Takagi from Tokyo Metropolitan University have created a chromic material that changes color in response to humidity.
What makes this film special is the mechanism by which it achieves such a striking change. The team used an environmentally-friendly clay mineral that has a layered structure with nanometer-scale spaces in between the layers. The team managed to fill these tiny gaps with a magnesium porphyrin dye.
In response to humidity, the spacing between the clay layers changes. This in turn affects the confinement of the dye. More specifically, the electrons surrounding the dye molecule—particularly those involved in how it interacts with light—are made to line up with certain chemical groups in the clay, dramatically changing its color.
No chemical bonds were broken or formed during this process. The researchers noted that this property makes the film more compatible with repeated switching, with less degradation of the material.
In addition to being more durable, the clay and the dye are derived from naturally-occurring materials. This means lower cost of production, improved safety and enhanced compatibility with the environment.
The article can be found at: Fujimura et al. (2018) Optical Humidity Sensing Using Transparent Hybrid Film Composed of Cationic Magnesium Porphyrin and Clay Mineral.
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Source: Tokyo Metropolitan University; Photo: Pixabay.
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