Abstract
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.
Highlights
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Inspired by able transmitted colors at given rotation angles (RA). Such properties are conveniently integrated into a “relative humidity (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
We introduce waterborne polyacrylic acid (PAA) as a commercially available and inexpensive anionic polyelectrolyte that fits in the left-handed CNC structure
Summary
We introduce waterborne PAA as a commercially available and inexpensive anionic polyelectrolyte that fits in the left-handed CNC structure. The crystalline and pore structure that result from self-assembled CNCs are transferred to CNC/PAA systems As a result, the latter combine the merits of ions and polymers as far as electrostatic repulsion, hydrogen bonding, and steric hindrance that regulate the shift of color in chiral nematic CNC/PAA during self-assembly (Figure 1b). The pitch of CNC/PAA iridescent coatings increased gradually with increasing PAA content, from 2 to 20 wt% (Figure 1f and Figure S2b,c, Supporting Information), corresponding to a gradual change in λmax from 430 to 568 nm (Figure S3, Supporting Information) This phenomenon is influenced by the enhanced electrostatic repulsion and steric hindrance of PAA. The samples were conditioned under variable relative humidity (RH) (Figure S5, Supporting Information)
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