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.

Additive manufacturing is becoming increasingly important as a flexible technique for a wide range of products, with applications in the transportation, health, and food sectors. However, to develop additional functionality it is important to simultaneously control structuring across multiple length scales. In 3D printing, this can be achieved by employing inks with intrinsic hierarchical order. Liquid crystalline systems represent such a class of self-organizing materials; however, to date they are only used to create filaments with nematic alignment along the extrusion direction. In this study, cholesteric hydroxypropyl cellulose (HPC) is combined with in situ photo-crosslinking to produce filaments with an internal helicoidal nanoarchitecture, enabling the direct ink writing of solid, volumetric objects with structural color. The iridescent color can be tuned across the visible spectrum by exploiting either the lyotropic or thermotropic behavior of HPC during the crosslinking step, allowing objects with different colors to be printed from the same feedstock. Furthermore, by examining the microstructure after extrusion, the role of shear within the nozzle is revealed and a mechanism proposed based on rheological measurements simulating the nozzle extrusion. Finally, by using only a sustainable biopolymer and water, a pathway toward environmentally friendly 3D printing is revealed.

history and recent progress of 1D photonic films, also commonly referred to as photonic multilayer structures. In the third section, recent advances in exploiting confined self-assembly of block copolymers to produce photonic pigments are introduced and the diversity of structures that can be achieved with this method explored, ranging from concentric lamellae to porous particles with correlated disorder. Finally, we conclude by highlighting promising directions for future investigation.

Hydroxypropyl cellulose (HPC) is an edible, cost‐effective and widely used derivative of cellulose. Under lyotropic conditions in water, HPC forms a photonic, liquid crystalline mesophase with an exceptional mechanochromic response. However, due to insufficient physical cross‐linking photonic HPC can flow freely as a viscous liquid, preventing the exploitation of this mechanochromic material in the absence of any external encapsulation or structural confinement. Here this challenge is addressed by mixing HPC and gelatin in water to form a self‐supporting, viscoelastic, and edible supramolecular photonic hydrogel. It is demonstrated that the structural coloration, mechanochromism and non‐Newtonian shear‐thinning behavior of the lyotropic HPC solutions can all be retained into the gel state. Moreover, the rigidity of the HPC‐gel provides a 69% shorter mechanochromic relaxation time back to its initial color when compared to the liquid HPC–water only system, broadening the dynamic color range of HPC by approximately 2.5× in response to a compressive pressure. Finally, the ability to formulate the HPC‐gels in a scalable fashion from only water and “food‐grade” constituents unlocks a wide range of potential applications, from response‑tunable mechanochromic materials and colorant‐free food decoration, to short‐term sensors in, for example, biodegradable “smart labels” for food packaging.

The position of methyl groups causes a dramatic change in molecular properties and solar cell performance.