Manipulating
functional stimuli-responsive materials has been a
hot topic in the research of smart sensors and anticounterfeiting
encryption. Here, a novel functional chiral nematic cellulose nanocrystal
(CNC) film showing dual responsiveness to humidity and formaldehyde
gas was fabricated. The chiral nematic CNC iridescent film could respond
to environmental humidity and formaldehyde gas changes by reversible
motion. Interestingly, the humidity sensitivity of the CNC iridescent
film could be gated by exposing the film to formaldehyde gas. At the
same time, the formaldehyde-responsive behavior is strongly affected
by the relative humidity (RH), and the response range could be tuned
by changing the RH over a wide range. Importantly, the formaldehyde-induced
color change could be altered from invisible to visible by the naked
eye when the film was exposed to a humid environment. The mechanism
of this dual response of the CNC iridescent film is ascribed to the
synergistic effect of cooperation and competition between water and
formaldehyde molecules by constructing physical cross-linking networks
by hydrogen bonds among water, formaldehyde, and CNCs. Furthermore,
the “RH-concentration of formaldehyde gas-color” ternary
colorimetric system was simulated, which is thought to endow the CNC
iridescent film with great potential to act as a sensor in the convenient
visible detection of gaseous formaldehyde. Furthermore, this work
provided a promising strategy to design multi-gas-sensitive devices
with convenient detection, good stability, and excellent reversibility.
The need for a precise regulation of the properties of chiral nematic structures in response to external stimuli is addressed. Self‐assembled iridescent coatings are produced under the effect of electrostatic interactions between cellulose nanocrystals and poly(acrylic acid), endowing a high anisotropic dissymmetry (>0.3) and sensitivity to environmental humidity (13.1 nm/1% at 68–75% relative humidity, RH). The phenomena associated with shifts in selective light reflection (green to orange) and polarization, facilitate tunable transmitted colors (blue to orange) at given rotation angles (RA). Such properties are conveniently integrated into a “RH‐RA‐color” ternary code that is introduced as an anticounterfeiting technology, taking advantage of multicolor patterns that conveniently track with changes in RH and RA. The proposed charge‐driven assembly opens new opportunities for chiral nematic materials that enable precise optical sensing and information encryption.
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