Non-iridescent and Wide-Color-Range Structural Coloration Enabled by Cellulose Nanocrystals with a Controlled Long-Range Photonic Structure and Helical Pitch

Abstract

Bioinspired coloration of cellulose nanocrystals (CNCs) has advanced a new era of wide applications for decoration, sensing, and anti-counterfeiting. However, the solid structural color films suffer from strong angle-dependent iridescence and a limited color range due to the spatial arrangement caused by kinetic arrest during evaporation-induced self-assembly of CNCs. Here, a ternary co-assembly approach is demonstrated to prepare CNC films with weak/non-angular optical response and wide-range colors. Structural coloration is enabled by the long-range and short-range ordered photonic structure of CNCs. A cationic polymer, poly­(dimethyl diallyl ammonium chloride), is introduced to influence the CNC self-assembly through electrostatic attraction, inducing the structural transition to the long-range disordered/short-range ordered structure as well as presenting the gradual change from iridescent structural colors to non-iridescent colors. Additionally, a hydrophilic small compound, glycerol, is used to adjust the helical pitch of nanostructured CNC arrays, offering the broad-range coloration. The CNC-based composite material is further used as an optical coating for anti-counterfeiting and realizing color patterning and angle-dependent selective color changes.

Structural Color from Cellulose Nanocrystals or Chitin Nanocrystals: Self-Assembly, Optics, and Applications

“…Notably, when only a small amount of cationic polymer is added (e.g., ≪ 2 wt % PDDA relative to CNC) the destabilization of the CNCs instead leads to an earlier kinetic arrest, resulting in highly polydomain films that displays desaturated, noniridescent color. , Alternatively, inclusion of a zwitterionic surfactant into the aqueous CNC suspension gives rise to a similar red-shift to that observed for neutral additives, which could be attributed to the surfactant instead forming “noninteracting” micelles within the cholesteric suspension. As such, this can be seen as analogous to when CNC films are cocast with small latex nanoparticles (e.g., D hyd ≈ 50 nm) .…”

“…The simplest method to enhance functionality is by including a water dispersible, “noninteracting” additive into the initial CNC suspension (e.g., glucose, ,− glycerol, ,, latex − ). Upon casting a film, the presence of a nonvolatile additive prevents the CNC concentration from reaching 100 vol% and therefore reduces the final compression of the CNC mesophase (see section ).…”

“…simplest method to enhance functionality is by including a water dispersible, "noninteracting" additive into the initial CNC suspension (e.g., glucose, 436,725−728 glycerol,680,729,730 …”

Design Strategies for Creating Cellulose-Based Nanomaterials with Tailored Optical Functionality

“…(f) Photographs of the CNC/glycerol composite films at various viewing angles. Reproduced from ref .…”

Thermo-Sensitive Poly(p-dioxanone) Banded Spherulites with Controllable Patterns for Iridescence

“…The chiral nematic morphology of cellulose with layered assembly resulted in brilliant blue coloration on Pollia Condensata fruit’s skin . Cellulose nanocrystals (CNCs) are isolated by controlled acid hydrolysis and peculiarly resemble the natural chiral-nematic structure in the synthetic condition. − Pigmented barbules coupled with periodic structural coloration produce attractive iridescences in peacock feathers . The layered nanostructure of nacre (CaCO 3 in pearls or sea-shells) generates pleasant metallic-shiny photonic reflection. , Synthetic block-copolymers may form nanophase separation between blocks in sub-10 nm level with a winkled texture .…”