Mind the Microgap in Iridescent Cellulose Nanocrystal Films

Fernandes, Susete N.; Almeida, Pedro L.; Monge, Nuno; Aguirre, Luis E.; Reis, Dennys; Oliveira, Cristiano L. P.; Neto, Antônio Martins Figueiredo; Pierański, P.; Godinho, M. H.

doi:10.1002/adma.201603560

Cited by 186 publications

(186 citation statements)

References 37 publications

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“…Cellulose nanocrystals were obtained from the acid hydrolysis of microcrystalline cellulose (MCC; Aldrich Avicel®,~50 µm particle size, derived from cotton) with sulphuric acid (Sigma-Aldrich, 95-97% purity), as described elsewhere by Fernandes et al [25], however a reaction time of 40 min instead of 130 min was used. A lower reaction time was selected since the authors confirmed that the particles produced by these conditions were very similar to the ones synthesized using longer reaction times.…”

Section: Methodsmentioning

confidence: 99%

Flexible and Structural Coloured Composite Films from Cellulose Nanocrystals/Hydroxypropyl Cellulose Lyotropic Suspensions

et al. 2020

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Lyotropic colloidal aqueous suspensions of cellulose nanocrystals (CNCs) can, after solvent evaporation, retain their chiral nematic arrangement. As water is removed the pitch value of the suspension decreases and structural colour-generating films, which are mechanically brittle in nature, can be obtained. Increasing their flexibility while keeping the chiral nematic structure and biocompatible nature is a challenging task. However, if achievable, this will promote their use in new and interesting applications. In this study, we report on the addition of different amounts of hydroxypropyl cellulose (HPC) to CNCs suspension within the coexistence of the isotropic-anisotropic phases and infer the influence of this cellulosic derivative on the properties of the obtained solid films. It was possible to add 50 wt.% of HPC to a CNCs aqueous suspension (to obtain a 50/50 solids ratio) without disrupting the LC phase of CNCs and maintaining a left-handed helical structure in the obtained films. When 30 wt.% of HPC was added to the suspension of CNCs, a strong colouration in the film was still observed. This colour shifts to the near-infrared region as the HPC content in the colloidal suspension increases to 40 wt.% or 50 wt.% The all-cellulosic composite films present an increase in the maximum strain as the concentration of HPC increases, as shown by the bending experiments and an improvement in their thermal properties.

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Section: Methodsmentioning

confidence: 99%

Flexible and Structural Coloured Composite Films from Cellulose Nanocrystals/Hydroxypropyl Cellulose Lyotropic Suspensions

et al. 2020

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“…[1] Cellulose nanocrystals (CNCs) are an excellent example of such a biosourced nanomaterial, owing to a unique combination of chemical, mechanical, and optical properties, [2,3] which explains the increase of interest in this system for applications as pigments, [4] security coatings, [5,6] sensing or responsive materials, [7][8][9][10][11][12] and mesoporous chiral nanotemplates. Such approaches can offer a cost-effective and scalable solution to design materials with a desired optical response.…”

Section: Nanocrystal Filmsmentioning

confidence: 99%

Controlling the Photonic Properties of Cholesteric Cellulose Nanocrystal Films with Magnets

et al. 2017

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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.

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“…Because of the negative sulfate half-esters or other surface charges remaining from the production procedure, CNCs are easily dispersed in water. Adding their excellent mechanical properties, optical transparency, ease of chemical functionalization, and ability to form a longrange-ordered LC phase, CNCs are highly attractive for the realization of tunable, in some cases even responsive, highperformance materials with spectacular mechanical and optical properties 5,9,[13][14][15] . The LC phase formed by CNC suspensions is of the chiral nematic, or cholesteric, type.…”

Section: Introductionmentioning

confidence: 99%

Fractionation of cellulose nanocrystals: enhancing liquid crystal ordering without promoting gelation

et al. 2018

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Colloids of electrically charged nanorods can spontaneously develop a fluid yet ordered liquid crystal phase, but this ordering competes with a tendency to form a gel of percolating rods. The threshold for ordering is reduced by increasing the rod aspect ratio, but the percolation threshold is also reduced with this change; hence, prediction of the outcome is nontrivial. Here, we show that by establishing the phase behavior of suspensions of cellulose nanocrystals (CNCs) fractionated according to length, an increased aspect ratio can strongly favor liquid crystallinity without necessarily influencing gelation. Gelation is instead triggered by increasing the counterion concentration until the CNCs lose colloidal stability, triggering linear aggregation, which promotes percolation regardless of the original rod aspect ratio. Our results shine new light on the competition between liquid crystal formation and gelation in nanoparticle suspensions and provide a path for enhanced control of CNC self-organization for applications in photonic crystal paper or advanced composites.

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Mind the Microgap in Iridescent Cellulose Nanocrystal Films

Cited by 186 publications

References 37 publications

Flexible and Structural Coloured Composite Films from Cellulose Nanocrystals/Hydroxypropyl Cellulose Lyotropic Suspensions

Flexible and Structural Coloured Composite Films from Cellulose Nanocrystals/Hydroxypropyl Cellulose Lyotropic Suspensions

Controlling the Photonic Properties of Cholesteric Cellulose Nanocrystal Films with Magnets

Fractionation of cellulose nanocrystals: enhancing liquid crystal ordering without promoting gelation

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