Chameleon-Inspired Variable Coloration Enabled by a Highly Flexible Photonic Cellulose Film

Due to spontaneous organization of
cellulose nanocrystals (CNCs)
into the chiral nematic structure that can selectively reflect circularly
polarized light within a visible-light region, fabricating stretching
deformation-responsive CNC materials is of great interest but is still
a big challenge, despite such a function widely observed from existing
creatures, like a chameleon, because of the inherent brittleness.
Here, a flexible network structure is introduced in CNCs, exerting
a bridge effect for the rigid nanomaterials. The as-prepared films
display high flexibility with a fracture strain of up to 39%. Notably,
stretching-induced structural color changes visible to the naked eye
are realized, for the first time, for CNC materials. In addition,
the soft materials show humidity- and compression-responsive properties
in terms of changing apparent structural colors. Colored marks left
by ink-free writing can be shown or hidden by controlling the environmental
humidities. This biobased photonic film, acting as a new “smart
skin”, is potentially used with multifunctions of chromogenic
sensing, encryption, and anti-counterfeit.