Visual Appearance of Chiral Nematic Cellulose‐Based Photonic Films: Angular and Polarization Independent Color Response with a Twist

Abstract

Hydroxypropyl cellulose (HPC) is a biocompatible cellulose derivative capable of self‐assembling into a lyotropic chiral nematic phase in aqueous solution. This liquid crystalline phase reflects right‐handed circular polarized light of a specific color as a function of the HPC weight fraction. Here, it is demonstrated that, by introducing a crosslinking agent, it is possible to drastically alter the visual appearance of the HPC mesophase in terms of the reflected color, the scattering distribution, and the polarization response, resulting in an exceptional matte appearance in solid‐state films. By exploiting the interplay between order and disorder, a robust and simple methodology toward the preparation of polarization and angular independent color is developed, which constitutes an important step toward the development of real‐world photonic colorants.

Flexible and Structural Coloured Composite Films from Cellulose Nanocrystals/Hydroxypropyl Cellulose Lyotropic Suspensions

“…Further increase in the HPC content leads to films with no iridescence and develops a matte finish (Figure 3k,l). This type of matte finish was reported recently by Chan et al on cross-linked HPC coloured films [35] and the authors attributed this observation to a large multiplicity of pitches within the sample. From SEM images obtained from the cross-section of our films, it is easy to see that the chiral nematic arrangement on the composite's samples, up to an intake of 30 wt.% of HPC (Figure 3d-f,m), is retained after solvent evaporation, although the pitch value (defined as the value measure for each 2 consecutive layers) increases.…”

Chiral Photonic Liquid Crystal Films Derived from Cellulose Nanocrystals

“…Reproduced with permission. [211] Copyright 2019, John Wiley and Sons. g) Schematic of the circular polarization-dependent reflection from perfect and distorted helicoids.…”

Orientation Control of Helical Nanofilament Phase and Its Chiroptical Applications

“…λ = 2ndcosθ (3) Interestingly, HNF has an amorphous photonic crystal property. In Figure 10, the pseudo-1D layer formed by oriented HNF (red dashed line in Figure 10a) has a certain degree of undulation, so the crystal orientation is weakened, and the angle-dependent color change is suppressed (Figure 15f) [96][97][98]. For these reasons, HNF is expected to be superior to the conventional fluid CLC phases, which can be used in more advanced chiroptical applications such as patternable photonic crystals with enhanced stability and reduced angle-dependency.…”