Structure–color mechanism of iridescent cellulose nanocrystal films

Liu, Dagang; Wang, Shuo; Ma, Zhongqing; Tian, Donglin; Gu, Mingyue; Lin, Fengying

doi:10.1039/c4ra06268j

Cited by 86 publications

(65 citation statements)

References 34 publications

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“…According to the literature, we also found that the cholesteric order is conserved for micrometer‐scale distances, much larger than the nanometric length of the CNC rods. The lateral size of the domains was found to be dependent upon many factors, which include the initial film precursor solutions' characteristics as well as the films' production conditions . The cross‐section heterogeneities are in agreement with the literature: not only the existence of cholesteric planar layers with different pitches but also the micrometer gaps in between .…”

supporting

confidence: 85%

“…The optical properties of the films were found to depend upon the characteristics of the colloidal suspensions, which pass through different stages upon solvent evaporation and before the formation of the film. In order to use these films for optical applications, many attempts have been undertaken to control their optical properties and mainly their reflection characteristics . If casting followed by a slow solvent‐evaporation method is used, the resulting films show iridescent colors and its cross‐sections can present several domains with different pitch values.…”

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confidence: 99%

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Mind the Microgap in Iridescent Cellulose Nanocrystal Films

et al. 2016

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A new photonic structure is produced from cellulose nanocrystal iridescent films reflecting both right and left circularly polarized light. Micrometer‐scale planar gaps perpendicular to the films' cross‐section between two different left‐handed films' cholesteric domains are impregnated with a nematic liquid crystal. This photonic feature is reversibly tuned by the application of an electric field or a temperature variation.

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confidence: 85%

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confidence: 99%

Mind the Microgap in Iridescent Cellulose Nanocrystal Films

et al. 2016

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“…We also tuned the ultrasonic time and temperature to reduce the FWHM of included‐angle, as shown in Figures and , respectively. The aim is to study the potential effect of ultrasonic time and temperature on the dispersion state of SCNC in water . The FWHM of included angle then decreased to be as small as 6.73° at 35 °C and 25 min, as shown in Figure d and its inset.…”

Section: Resultsmentioning

confidence: 99%

“…The aim is to study the potential effect of ultrasonic time and temperature on the dispersion state of SCNC in water. [27] The FWHM of included angle then decreased to be as small as 6.73° at 35 °C and 25 min, as shown in Figure 1d and its inset. When the ultrasonic time was too long, the CNC broke, leading to a change in the size of CNC (as shown in Figure S2 in the Supporting Information) and further a less regular arrangement of CNC.…”

Section: Introductionmentioning

confidence: 81%

Assembly‐Induced Emission of Cellulose Nanocrystals for Hiding Information

Gan

Feng

Liu

et al. 2019

Part & Part Syst Charact

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Fluorescent‐labeled cellulose nanocrystal (CNC) films have been used to record and protect information in paper materials, whereas the fluorescent materials usually suffer photobleaching. Herein, a strategy of solid‐state emission induced by the vertical assembly of CNCs was established. The assembly‐induced emission starts from the structural diffraction of CNC, whose wavelength is adjusted into the ultraviolet (UV) region for hiding information under natural light. The small diameter (≈10 nm) of CNCs then promotes the resonance between the vertically assembled CNCs and the UV light, leading to a strong blue emission with an emitting quantum efficiency as high as 13.90%. By introducing the vertical‐assembly film with a specific pattern into paper materials, an anti‐counterfeiting image is obtained under a UV radiation. Since CNCs are a kind of cellulose with high crystallinity, this material can be a wear‐resistant anti‐counterfeiting material for banknotes or other paper applications.

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“…Because of the structure, the films behave as 1D photonic crystals, reflecting circularly polarized light having the same sense as the cholesteric screw orientation . This property of CNCs is attractive for producing iridescent films with many potential applications …”

Section: Methodsmentioning

confidence: 99%

Broadband Circular Polarizing Film Based on Chiral Nematic Liquid Crystals

Cao

Hamad

MacLachlan

2018

Advanced Optical Materials

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polarizers use birefringent crystals requiring a specific thickness and suffer from bulky configurations, [13] many efforts have focused on cholesteric liquid crystals, such as cholesteric polymer networks with a pitch gradient, [14][15][16] or have focused on newly functional optical materials such as compact 3D gold helix metamaterials [3,17,18] and broadband graphene fiber polarizers. [19] Because these approaches are costly and challenging to scale, an inexpensive and straightforward method to achieve broadband circular polarization is in demand.Cellulose is the most abundant biopolymer in nature and can be produced from several natural resources, including plants, tunicates, or bacteria. [20,21] Treatment of extracted cellulose fibers with sulfuric acid produces cellulose nanocrystals (CNCs) with negatively charged sulfate half-ester surface groups. [22,23] This surface charge, whose electrostatic repulsion allows CNCs to form stable colloidal dispersions in water, gives CNCs unique selfassembling properties. Above a critical concentration, CNCs spontaneously organize into a chiral nematic lyotropic liquid crystal, and the structure is retained in films of CNCs following evaporation of the water. [24,25] This chiral nematic mesophase is characterized by stacked layers of oriented CNC spindles, where the orientations of the spindles within the layers rotate with a characteristic twist. Because of the structure, the films behave as 1D photonic crystals, reflecting circularly polarized light having the same sense as the cholesteric screw orientation. [26] This property of CNCs is attractive for producing iridescent films with many potential applications. [27][28][29][30][31][32][33][34] The wavelength reflected from a chiral nematic structure depends on a modified Bragg's Law, λ = nPcosθ, [35] where n is the average refraction index, P is the helical pitch length, and θ corresponds to the angle between incident light propagation direction and the helix axis. Thus, for a specified refractive index (usually determined by the components), the wavelength of the reflected light varies as a function of θ and P. As a result, both nonuniform pitch lengths and a distribution of helical axis orientations would lead to wide-band reflection.For lyotropic liquid crystals of CNCs, the assembly from an isotropic phase into a dense, anisotropic layered structure is a dynamic process that can be influenced by factors such as the pH, ionic strength, additives, and surface tension. [36][37][38][39] This dynamic self-assembly opens the path to introducing defects into the CNC films that lead to different pitches and/or orientations, giving a variety of reflection bands. In this work, we designed a micelle-assisted assembly approach to modulate the Films capable of broadband circular polarization of light are important for many optical applications. Owing to their intrinsic chiral nematic mesostructure, freestanding films of cellulose nanocrystals can reflect circularly polarized light, but this is typically restricted to a narrow ...

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Structure–color mechanism of iridescent cellulose nanocrystal films

Cited by 86 publications

References 34 publications

Mind the Microgap in Iridescent Cellulose Nanocrystal Films

Mind the Microgap in Iridescent Cellulose Nanocrystal Films

Assembly‐Induced Emission of Cellulose Nanocrystals for Hiding Information

Broadband Circular Polarizing Film Based on Chiral Nematic Liquid Crystals

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