By controlling the interaction of biological building blocks at the nanoscale, natural photonic nanostructures have been optimized to produce intense coloration. Inspired by such biological ...nanostructures, the possibility to design the visual appearance of a material by guiding the hierarchical self‐assembly of its constituent components, ideally using natural materials, is an attractive route for rationally designed, sustainable manufacturing. Within the large variety of biological building blocks, cellulose nanocrystals are one of the most promising biosourced materials, primarily for their abundance, biocompatibility, and ability to readily organize into photonic structures. Here, the mechanisms underlying the formation of iridescent, vividly colored materials from colloidal liquid crystal suspensions of cellulose nanocrystals are reviewed and recent advances in structural control over the hierarchical assembly process are reported as a toolbox for the design of sophisticated optical materials.
Bioinspired optical materials fabricated from naturally derived cellulose nanocrystals attract considerable interest due to their complex photonic behavior. The underlying mechanisms responsible for the hierarchical assembly of the colloidal liquid crystal suspension and its translation into the solid state to give vivid, iridescently colored materials are highlighted. This provides a toolbox for the design of novel optical materials.
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Aqueous colloidal suspensions, both man-made and natural, are part of our everyday life. The applicability of colloidal suspensions, however, is limited by the range of conditions over which they are ...stable. Here we report a novel type of highly monodisperse raspberry-like colloids, which are prepared in a single-step synthesis that relies on simultaneous dispersion and emulsion polymerisation. The resulting raspberry colloids behave almost like hard spheres. In aqueous solutions, such prepared raspberries show unexpected stability against aggregation over large variations of added salt concentrations without addition of stabilisers. We present simple Derjaguin-Landau-Verwey-Overbeek (DLVO) calculations performed on raspberry-like and smooth colloids showing that this stability results from our raspberries' unique morphology, which extends our understanding of colloidal stability against salting. Further, the raspberries' stability facilitates the formation of superspheres and thin films in which the raspberry colloids self-assemble into hexagonally close-packed photonic crystals with exquisite reproducibility.
Abstract
The quest for flexible curvilinear displays is driving renewed interest in natural soft photonic systems that rely on the adaptable response of nanostructured living tissues to external ...stimuli for camouflage and energy management. Understanding and controlling the dynamics of these systems is challenging due to difficulties in sourcing the tissues and constraints in the ability to stimulate them. Here, we present an ex-vivo approach to systematically investigate soft biophotonic crystals and dynamically control their response by using the
Bos taurus
tapetum as a model system. The tapetum’s structural color is controlled chemically and electronically and examined by multispectral imaging providing insights on the color change dynamics. The ability to spatio-temporally control the optical response of biophotonic crystals provides insights for the development of soft photonic systems for displays and dynamic light management.
Silk Fibroin (SF) obtained from
is a very attractive biopolymer that can be useful for many technological applications, from optoelectronics and photonics to biomedicine. It can be processed from ...aqueous solutions to obtain many scaffolds. SF dissolution is possible only with the mediation of chaotropic salts that disrupt the secondary structure of the protein. As a consequence, recovered materials have disordered structures. In a previous paper, it was shown that, by modifying the standard Ajisawa's method by using a lanthanide salt, CeCl
, as the chaotropic agent, it is possible to regenerate SF as a fibrous material with a very ordered structure, similar to that of the pristine fiber, and doped with Ce
ions. Since SF exhibits a moderate fluorescence which can be enhanced by the incorporation of organic molecules, ions and nanoparticles, the possibility of doping it with lanthanide ions could be an appealing approach for the development of new photonic systems. Here, a systematic investigation of the behavior of degummed SF in the presence of all lanthanide ions, Ln
, is reported. It has been found that all lanthanide chlorides are chaotropic salts for solubilizing SF. Ln
ions at the beginning and the end of the series (La
, Pr
, Er
, Tm
, Yb
, Lu
) favor the reprecipitation of fibrous SF as already found for Ce
. In most cases, the obtained fiber preserves the morphological and structural features of the pristine SF. With the exception of SF treated with La
, Tm
, and Lu
, for all the fibers re-precipitated a concentration of Ln
between 0.2 and 0.4% at was measured, comparable to that measured for Ce
-doped SF.
Cephalopods camouflage abilities arise from highly specialized chromatic elements in their skin, chromatophores, iridophores, and leucophores, that enable them to display complex and rapidly changing ...color patterns. Despite the extensive study of these chromatic elements in squid and cuttlefish, full characterization of their individual optical response is still elusive in the
species. We present here detailed multispectral analysis and mapping of the
skin that allows to precisely identify the spatial distribution of the animal’s pigmented and structural elements. The mutual interaction of chromatophores and iridophores is also characterized both in terms of spectral response and spatial localization. The spectral information obtained through this analysis helps to understand the complexity and behavior of these natural tissues while continuing to serve as an inspiration for the fabrication of advanced, chromatically adaptable materials.
The fabrication of self‐assembled cellulose nanocrystal (CNC) films of tunable photonic and mechanical properties using a facile, green approach is demonstrated. The combination of tunable ...flexibility and iridescence can dramatically expand CNC coating and film barrier capabilities for paints and coating applications, sustainable consumer packaging products, as well as effective templates for photonic and optoelectronic materials and structures.
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The self‐assembly of cellulose nanocrystals is a powerful method for the fabrication of biosourced photonic films with a chiral optical response. While various techniques have been exploited to tune ...the optical properties of such systems, the presence of external fields has yet to be reported to significantly modify their optical properties. In this work, by using small commercial magnets (≈ 0.5–1.2 T) the orientation of the cholesteric domains is enabled to tune in suspension as they assemble into films. A detailed analysis of these films shows an unprecedented control of their angular response. This simple and yet powerful technique unlocks new possibilities in designing the visual appearance of such iridescent films, ranging from metallic to pixelated or matt textures, paving the way for the development of truly sustainable photonic pigments in coatings, cosmetics, and security labeling.
Commercial magnets can be used to control the optical properties of cholesteric cellulose nanocrystals films, resulting in photonic structures with an unprecedented photonic response. This striking effect unlocks new possibilities in the already broad range of photonic applications of such systems; from colorants, to sensors and security devices.
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Complex hierarchical architectures are ubiquitous in nature. By designing and controlling the interaction between elementary building blocks, nature is able to optimize a large variety of materials ...with multiple functionalities. Such control is, however, extremely challenging in man-made materials, due to the difficulties in controlling their interaction at different length scales simultaneously. Here, hierarchical cholesteric architectures are obtained by the self-assembly of cellulose nanocrystals within shrinking, micron-sized aqueous droplets. This confined, spherical geometry drastically affects the colloidal self-assembly process, resulting in concentric ordering within the droplet, as confirmed by simulation. This provides a quantitative tool to study the interactions of cellulose nanocrystals beyond what has been achieved in a planar geometry. Our developed methodology allows us to fabricate truly hierarchical solid-state architectures from the nanometer to the macroscopic scale using a renewable and sustainable biopolymer.
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Hierarchical, structurally colored materials offer a wide variety of visual effects that cannot be achieved with standard pigments or dyes. However, their fabrication requires simultaneous control ...over multiple length-scales. Here we introduce a robust strategy for the fabrication of hierarchical photonic pigments via the confined self-assembly of bottlebrush block copolymers within emulsified microdroplets. The bottlebrush block copolymer self-assembles into highly ordered concentric lamellae, giving rise to a near perfect photonic multilayer in the solid state, with reflectivity up to 100%. The reflected color can be readily tuned across the whole visible spectrum by either altering the molecular weight or by blending the bottlebrush block copolymers. Furthermore, the developed photonic pigments are responsive, with a selective and reversible color change observed upon swelling in different solvents. Our system is particularly suited for the scalable production of photonic pigments, arising from their rapid self-assembly mechanism and size-independent color.
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Artificial microcilia structures have shown potential to incorporate actuators in various applications such as microfluidic devices and biomimetic microrobots. Among the multiple possibilities to ...achieve cilia actuation, magnetic fields present an opportunity given their quick response and wireless operation, despite the difficulty in achieving localized actuation because of their continuous distribution. In this work, a high‐aspect‐ratio (>8), elastomeric, magnetically responsive microcilia array is presented that allows for wireless, localized actuation through the combined use of light and magnetic fields. The microcilia array can move in response to an external magnetic field and can be locally actuated by targeted illumination of specific areas. The periodic pattern of the microcilia also diffracts light with varying diffraction efficiency as a function of the applied magnetic field, showing potential for wirelessly controlled adaptive optical elements.
Chromium dioxide/poly(dimethylsiloxane) composite micropillars with high aspect‐ratio and magnetic properties are presented. The microcilia can be remotely actuated either collectively or selectively by using magnetic fields and light. Light‐driven local actuation enables this microcilia array to function as reconfigurable and controllably moving subsets.
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