Hierarchical Self-Assembly of Cellulose Nanocrystals in a Confined Geometry

Abstract

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.

Controlling the Photonic Properties of Cholesteric Cellulose Nanocrystal Films with Magnets

“…The mismatch between these two tilt values indicates that other phenomena also play an important role in defining the initial alignment β i of the cholesteric domains under magnetic field. We believe that the anchoring will get stronger upon further drying as the vertical confinement increases, [62,75] contingent that it occurs before the sample becomes kinetically arrested. [30,36,72] Moreover, the alignment of cholesteric fields under both external fields and conflicting anchoring conditions usually involves a Fréedericksz transition.…”

The Self‐Assembly of Cellulose Nanocrystals: Hierarchical Design of Visual Appearance

“…c) Polarized optical microscopy image of a typical fingerprint pattern of the cholesteric phase. a–c) Reproduced under the terms of the CC‐BY 4.0 license . Copyright 2014, The Authors, published by American Chemical Society.…”

“…However, the intrinsic birefringence, together with the high aspect ratio of CNCs and the optical index of the surrounding media, leads to the emergence of an extrinsic birefringence for individual CNCs relative to their long axis . Collectively, the arrangement of such CNCs, in terms of packing and degrees of alignment, will either cancel out in the isotropic phase or lead, in the anisotropic phase, to the emergence of a local birefringence …”

Nanocellulose Fragmentation Mechanisms and Inversion of Chirality from the Single Particle to the Cholesteric Phase

“…Nanocellulose, mainly in the form of sulfate half-ester modified CNC, is known to selfassemble into cholesteric liquid crystalline phases 9 . This discovery has opened up an entire field of research on sulfated nanocellulose cholesterics 10,[19][20][21][22][23][24] . While the results are impressive, the detailed mechanism behind the formation of the cholesteric phase remains unresolved 25 .…”