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

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.     

Cephalopod-Inspired Stretchable Self-Morphing Skin Via Embedded Printing and Twisted Spiral Artificial Muscles

Cutaneous muscles drive the texture-modulation behavior of cephalopods by protruding several millimeters out of the skin. Inspired by cephalopods, a self-morphing, stretchable smart skin containing embedded-printed electrodes and actuated by Twisted Spiral Artificial Muscles (TSAMs) is proposed. Electrothermally actuated TSAMs are manufactured from inexpensive polymer fibers to mimic the papillae muscles of cephalopods. These spirals can produce strains of nearly 2000% using a voltage of only 0.02 V mm⁻¹. Stretchable and low-resistance liquid metal electrodes are embedded-printed inside the self-morphing skin to facilitate the electrothermal actuation of TSAMs. Theoretical and numerical models are proposed to describe the embedded printing of low-viscosity Newtonian liquid metals as conductive electrodes in a soft elastomeric substrate. Experimental mechanical tests are performed to demonstrate the robustness and electrical stability of the electrodes. Two smart skin prototypes are fabricated to highlight the capabilities of the proposed self-morphing system, including a texture-modulating wearable soft glove and a waterproof skin that emulates the texture-modulation behavior of octopi underwater. The proposed self-morphing stretchable smart skin can find use in a wide range of applications, such as refreshable Braille displays, haptic feedback devices, turbulence tripping, and antifouling devices for underwater vehicles.     

Printing of Responsive Photonic Cellulose Nanocrystal Microfilm Arrays

Interactive materials capable of changing appearance upon exposure to external stimuli, such as photonic inks, are generally difficult to achieve on a large scale as they often require self‐assembly processes that are difficult to control macroscopically. Here this problem is overcome by preparing arrays of cellulose nanocrystal (CNC) microfilms from discrete nanoliter sessile droplets. The obtained microfilms show extremely uniform and intense color, enabling exceptional consistency in optical appearance across the entire array. The color can be controlled through the initial ink formulation, enabling the printing of polychromatic dot‐matrix images. Moreover, the high surface‐to‐volume ratio of the microfilms and the intrinsic hydrophilicity of the natural building block allow for a dramatic real‐time colorimetric response to changes in relative humidity. The printed CNC microfilm arrays overcome the existing issues of scalability, optical uniformity, and material efficiency, which have held back the adoption of CNC‐based photonic materials in cosmetics, interactive‐pigments, or anticounterfeit applications.