Abstract
Cellulose nanocrystals (CNCs), produced by the acid hydrolysis of wood, cotton or other cellulose-rich sources, constitute a renewable nanosized raw material with a broad range of envisaged uses: f ...
Highlights
We focus on the macroscopic phase behavior and the balance between liquid crystalline ordering and a transition into a gel-like glassy state
CONCLUDING REMARKS AND OUTLOOK The study of cellulose nanocrystals (CNCs) and their suspensions is a fascinating research field that has attracted significant interest, largely because of the potential of CNCs to be used as a renewable nanomaterial with the capacity for self-assembly
Nanostructured films with a photonic band gap arising from the spontaneous helix formation in the cholesteric liquid crystal phase of CNC suspensions have been the focus of several studies
Summary
Nanomaterials based on renewable resources are attracting rapidly growing interest, both from a fundamental scientific point of view and from the perspective of developing novel structural and functional macroscopic materials.[1,2] Using nature-based nanomaterials offers ecological advantages, and the extraordinary mechanical performance and/or photonic crystal character of biological composites such as bone, nacre, wood, beetle scales and butterfly wings is an important inspiration for the development of new multifunctional materials.[3,4,5] full utilization of the intrinsic properties of nanosized starting materials requires the development of robust and versatile synthetic and processing routes to control assembly over several length scales.[6,7,8]. Compared with photonic crystals formed via non-liquid crystalline self-assembly of spherical colloidal particles,[28] the helical liquid crystalline self-assembly of rod-like CNC particles leads to a more complex internal structure, rendering the material chiral and adding sensitivity to circular polarization while, at the same time, dramatically enhancing the mechanical properties.[22] progress in this area is hampered by a number of important phenomena that remain unexplained, as well as a few controversies regarding the self-organization of CNCs. For instance, the notion that the reflected color is due to a photonic bandgap resulting from the helical structure has been challenged based on observations of a helix that is too long for Bragg reflection to take place in the visible wavelength range,[29] and a surprising dependence on the ionic strength of the phase sequence and helical pitch has been observed in some systems.[30] One of the aims of this critical review is to emphasize the physics and physical chemistry-related issues involved in CNC self-assembly by comparing it with similar processes in suspensions of other nanorod classes. The corresponding gelation phenomenon of CNCs (typically occurring at higher particle concentrations) is well-known, its consequences on the liquid crystal behavior and the structure that is obtained in dried samples has far not been discussed
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