A flexible color-changing film inspired by chameleon skin

Date:
October 21, 2020
Source:
American Chemical Society
Summary:
Chameleons can famously change their colors to camouflage
themselves, communicate and regulate their temperature. Scientists
have tried to replicate these color-changing properties for stealth
technologies, anti- counterfeiting measures and electronic displays,
but the materials have limitations. Now, researchers have developed
a flexible film that changes color in response to stretching,
pressure or humidity.



FULL STORY ========================================================================== Chameleons can famously change their colors to camouflage themselves, communicate and regulate their temperature. Scientists have tried to
replicate these color-changing properties for stealth technologies, anti-counterfeiting measures and electronic displays, but the materials
have limitations. Now, researchers have developed a flexible film that
changes color in response to stretching, pressure or humidity. They
report their results in ACS Applied Materials & Interfaces.


==========================================================================
By tensing or relaxing their skin, chameleons can change the way light
reflects from guanine crystals under the surface, producing what's known
as structural coloration. These structural colors are different from
the pigments that give many other creatures their hues. Scientists
have mimicked the crystalline nanostructures of chameleon skin in
various color-changing materials, but they're typically difficult to
produce, or they rely on non-renewable petroleum resources. In contrast, cellulose nanocrystals are a renewable material that can self-assemble
into a film with iridescent structural colors. However, the films are
typically fragile and, unlike chameleon skin, can't be stretched without breaking. Fei Song, Yu-Zhong Wang and colleagues wanted to develop a
highly flexible film made of cellulose nanocrystals that changes color
when stretched.

To increase the flexibility of cellulose nanocrystals, the researchers
added a polymer called PEGDA and used UV light to crosslink it to
the rod-shaped nanocrystals, producing films with bright iridescent
colors ranging from blue to red, depending on the PEGDA amount. The
films were both strong and flexible, stretching up to 39% of their
original length before breaking. During stretching, the color of one
film gradually changed from red to green, and then changed back when
relaxed. According to the researchers, this is the first time that
stretching- and relaxing-induced, reversible structural color changes
that are brilliant and visible to the naked eye have been realized for cellulose nanocrystal materials. The film also changed color with pressure
and humidity, allowing the team to show or hide writing made by an inkless
pen. The new bio- based smart skin could find applications in strain
sensing, encryption and anti-counterfeiting measures, the researchers say.


========================================================================== Story Source: Materials provided by American_Chemical_Society. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Ze-Lian Zhang, Xiu Dong, Yi-Ning Fan, Lu-Ming Yang, Lu He, Fei
Song, Xiu-
Li Wang, Yu-Zhong Wang. Chameleon-Inspired Variable Coloration
Enabled by a Highly Flexible Photonic Cellulose Film. ACS
Applied Materials & Interfaces, 2020; 12 (41): 46710 DOI:
10.1021/acsami.0c13551 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/10/201021130141.htm

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