Circularly polarized light (CPL) is central to photonic technologies. A key challenge lies in developing a general route for generation of CPL with tailored chiroptical activity using low‐cost raw ...materials suitable for scale‐up. This study presents that cellulose films with photonic bandgaps (PBG) and left‐handed helical sense have an intrinsic ability for circular polarization leading to PBG‐based CPL with extraordinary |g | values, well‐defiend handedness, and tailorable wavelength by the PBG change. Using such cellulose films, incident light ranging from near‐UV to near‐IR can be transformed to passive L‐CPL and R‐CPL with viewing‐side‐dependent handedness and |g | values up to 0.87, and spontaneous emission transformed to R‐CPL emission with |g | values up to 0.68. Unprecedented evidence is presented with theoretical underpinning that the PBG effect can stimulate the R‐CPL emission. The potential of cellulose‐based CPL films for polarization‐based encryption is illustrated. The evaporation‐induced self‐assembly coupled with nanoscale mesogens of cellulose nanocrystals opens new venues for technological advances and enables a versatile strategy for rational design and scalable manufacturing of organic and inorganic CPL films for photonic applications.
Chiral photonic cellulose films have intrinsic ability to generate and manipulate circularly polarized light (CPL) with extraordinary |g | values in a broad spectral regime. The CPL handedness is well defined, and the wavelength control is simple to realize. Photonic bandgap effects cause stimulated CPL. It presents a versatile and scalable strategy for customized CPL materials using renewable cellulose for photonic applications.
Chiral Photonic Polymers
In article number 2103309, Albertus P. H. J. Schenning, Michael G. Debije, and co‐workers show that using direct ink writing, unconventional chiral nematic objects can be ...generated, which show a bright iridescent color from normal incidence, or only from sharp angles of observation depending on the writing speed. The cover is a polarized optical microscopy image showing a detail from the free‐standing Morpho‐inspired print.
Rod-like cellulose nanocrystals (CNCs) show the intriguing liquid crystal self-assembly ability. The understanding of the self-assembly behavior of CNCs is of fundamental importance for constructing ...cellulose-based functional materials. The presented work explores how the liquid crystal self-assembly behavior of CNCs is affected by the grafted ionic liquids (IL) VBImBF4. The results demonstrate that the IL modified CNC (CNC-IL) with positive charged form chiral nematic structure in suspensions, which was normally observed in negative charged ones. Significantly, such liquid-crystalline organization can be obtained under much lower concentration (as low as 1.0 wt%) than that of the non-functionalized CNCs prepared from paper pulp (~ 3.0 wt%). Moreover, for CNC-IL concentrations varying from 1.0 to 4.0 wt%, the tactoids (showing obvious fingerprint texture) coexist with the disordered CNC phase, rather than separating into two phases. Unlike original CNCs, the pitch of chiral nematic tactoids increases with increasing concentration of CNC-IL. Our study suggests that the distinct liquid crystal self-assembly behavior of CNC-IL is related to the restricted mobility of CNCs rods due to the increase in CNCs particle size and the high viscosity of CNC-IL suspension as the result of IL surface modification. The study of the liquid crystal assembly behavior of IL modified CNCs provides some new insight to understand the intriguing chiral nematic self-assembly of CNCs and for construction of CNC-IL reinforced nanocomposites.
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•It is verified that CNC modified by ionic liquid (CNC-IL) can form chiral nematic tactoids.•CNC-IL can form a chiral nematic phase at a lower concentration than CNC-OSO3 and not separate into two phases.•Unlike original CNCs, the pitch of chiral nematic tactoids decreases with increasing concentration of CNC-IL.
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.
Solid‐state chiral nematic films that reflect colors across the entire visible spectrum are obtained by crosslinking hydroxypropyl cellulose with glutaraldehyde. The addition of crosslinker allows for control over the self‐assembly dynamics of the hydroxypropyl cellulose. This enables the optical response to be manipulated to obtain structurally colored films with low polarization and angular dependence.
An optically resolvable and thermally chiral‐switchable device for circularly polarized luminescence (CPL) is first constructed using a light‐emitting conjugated polymer film and a double‐layered ...chiral nematic liquid crystal (N*‐LC) cell. The double‐layered N*‐LC cell with opposite handedness at each layer is fabricated by adding each of two types of N*‐LCs into each of the cells, and the N*‐LCs consist of nematic LCs and chiral dopants with opposite chirality and different mole concentrations. The selective reflection band due to the N*‐LC is thermally shifted so that the band wavelength is close to the luminescence band of the racemic conjugated polymer, such as disubstituted polyacetylene (diPA), yielding CPL with opposite handedness and high dissymmetry factor values (|glum|) of 1.1–1.6 at low and high temperatures. The double‐layered N*‐LC cell bearing the temperature‐controlled selective reflection is useful for generating CPLs from racemic fluorescent materials and for allowing thermal chirality‐switching in CPLs, which present new possibilities for optoelectronic and photochemical applications.
An optically resolvable and thermally chiral‐switchable device for circularly polarized luminescence (CPL) is constructed using a light‐emitting conjugated polymer film and a double‐layered cell of chiral nematic liquid crystal (N*‐LC) with opposite handedness at each layer. The chirality switching of the CPL is achieved via selective reflections of the N*‐LCs with different helical senses.
This contribution to the special issue of Carbohydrate Polymers commemorating the 100th Anniversary of the Cellulose and Renewable Materials Division of the American Chemical Society is a personal ...account, from a research chemist’s point of view, of some aspects of the discovery, development and utilization of nanocellulosic materials. The main focus is on cellulose nanocrystals stabilized by sulfate half-ester surface charges.
The iridescence of structural color and its polarization characteristics originate from the nanoscale organization of materials. A major challenge in materials science is generating the bright, ...lustrous hues seen in nature through nanoscale engineering, while simultaneously controlling interaction of the material with different light polarizations. In this work, a suitable chiral nematic liquid crystal elastomer ink is synthesized for direct ink writing, which self‐assembles into a chiral photonic structure. Tuning the writing direction and speed leads to the programmed formation of a slanted photonic axis, which exhibits atypical iridescence and polarization selectivity. After crosslinking, a freely programmable, chiroptical photonic polymer material is obtained. The strongly perspective‐dependent appearance of the material can function as specialized anticounterfeit markers, as optical elements in decorative iridescent coatings, or, as demonstrated here, in optically based signaling features.
Inspired by natural examples of patterned iridescence, an ink based on a chiral nematic liquid crystal that can be processed with a direct ink writer 3D printer is shown. Tuning the writing direction and speed leads to the programmed formation of a slanted photonic axis that exhibits atypical iridescence and polarization selectivity.
Pressure‐responsive chiral photonic aerogels are fabricated by combining liquid crystal self‐assembly and ice‐templating processes. The aerogels have a hierarchical structure in which the primary 2D ...chiral nematic structured walls of cellulose nanocrystals form ribbons that support a secondary 3D cellular network. Owing to the flexibility of the aerogels in solvent, the 3D structure of the aerogel can easily be transformed to a 2D structure by pressure‐induced rearrangement. The aerogels vary from white in color, which arises from light scattering, to a reflective photonic crystal displaying bright iridescent colors that depend on the immersed solvent. A solvent‐sensitive ink that shows quick color response to different solvents is designed using the pressure‐responsive photonic aerogel. This material demonstrates a new response mechanism for the design of smart and mechanoresponsive photonic materials.
Photonic cellulose aerogels with hierarchical structures are fabricated by combining self‐assembly and ice templating. The secondary macroporous structure changes under pressure, triggering a change in the optical properties of the aerogel from light scattering to chiral light reflection mode. This discovery enables the fabrication of mechanoresponsive aerogels that reversibly switch between white and bright structural colors.
Engineering the helical structure of chiral photonic materials in three dimensions remains a challenge. 3D helix engineered photonic materials are fabricated by local stratification in a ...photopolymerizable chiral nematic liquid crystal. The obtained chiral photonic materials reflect both handedness of circular polarized light and show super‐reflectivity. Simulations match the experimentally observed photonic properties and reveal a distorted helical structure. 3D engineered polymer films can be made that reflect both left‐ and right handed circular and linear polarized light dependent and exhibit a changing color contrast upon altering the polarization of incident light. Hence, these 3D engineered photonic materials are of interest for new and emerging applications ranging from anti‐counterfeit labels and data encryption to aesthetics and super‐reflective films.
3D engineered photonic materials are of interest for emerging applications, such as anticounterfeit labels, data encryption, and super‐reflective films. 3D engineered chiral nematic‐liquid‐crystal materials, which exhibit a changing color contrast between the image and the surroundings upon changes in the polarization of incident light, are reported.
•Carboxylated tCNCs with uniform nanoscale dimensions were successfully prepared.•The formation of carboxylated tCNCs lyotropic N*-LCs was observed for the first time.•The critical concentration of ...phase separation for tCNCs suspension was 3.5 wt%.
Tunicate cellulose, extracted from the marine animal, has drawn increasing attention as the high crystallinity and aspect ratio. However, it is hard to prepare tunicate cellulose nanocrystals (tCNCs) with narrow size distribution in the traditional way, especially for the carboxylated samples, which also affects their lyotropic liquid crystal behavior to a certain extent. Herein, carboxylated tCNCs with uniform nanoscale dimensions and high surface charges density were prepared through ammonium persulfate (APS) oxidation and ultrasonic post-processing. Of particular interest, the formation of carboxylated tCNCs lyotropic chiral nematic liquid crystals was observed for the first time, which displayed obvious birefringence and fingerprint texture. Meanwhile, it was found that the critical concentration of phase separation for tCNCs suspension was around 3.5 wt% from the phase diagram. This study provides an efficient way to fabricate carboxylated tCNCs, and the self-assembly properties may lead to great potential applications in constructing advanced functional materials.
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