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Macroscopic Control of Helix Orientation in Films Dried from Cholesteric Liquid-Crystalline Cellulose Nanocrystal Suspensions
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Royal Institute of Technology, Sweden.
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Royal Institute of Technology, Sweden.ORCID iD: 0000-0002-0671-435X
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2014 (English)In: ChemPhysChem, ISSN 1439-4235, E-ISSN 1439-7641, Vol. 15, no 7, 1477-1484 p.Article in journal (Refereed) Published
Abstract [en]

The intrinsic ability of cellulose nanocrystals (CNCs) to self-organize into films and bulk materials with helical order in a cholesteric liquid crystal is scientifically intriguing and potentially important for the production of renewable multifunctional materials with attractive optical properties. A major obstacle, however, has been the lack of control of helix direction, which results in a defect-rich, mosaic-like domain structure. Herein, a method for guiding the helix during film formation is introduced, which yields dramatically improved uniformity, as confirmed by using polarizing optical and scanning electron microscopy. By raising the CNC concentration in the initial suspension to the fully liquid crystalline range, a vertical helix orientation is promoted, as directed by the macroscopic phase boundaries. Further control of the helix orientation is achieved by subjecting the suspension to a circular shear flow during drying.

Place, publisher, year, edition, pages
2014. Vol. 15, no 7, 1477-1484 p.
Keyword [en]
film growth, helical structures, liquid crystals, nanocrystalline cellulose, optical properties
National Category
Chemical Sciences
Research subject
Materials Chemistry
Identifiers
URN: urn:nbn:se:su:diva-105198DOI: 10.1002/cphc.201400062ISI: 000335515900025OAI: oai:DiVA.org:su-105198DiVA: diva2:732435
Funder
Knut and Alice Wallenberg Foundation
Note

AuthorCount:7;

Available from: 2014-07-04 Created: 2014-06-24 Last updated: 2017-12-05Bibliographically approved
In thesis
1. Fabrication of nanocellulose-based materials: Liquid crystalline phase formation and design of inorganic–nanocellulose hybrids
Open this publication in new window or tab >>Fabrication of nanocellulose-based materials: Liquid crystalline phase formation and design of inorganic–nanocellulose hybrids
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The increasing need to replace fossil fuels as a source of energy and raw material is resulting in extensive research efforts towards identifying and developing high performance materials and devices based on renewable sources. Cellulose being the most versatile and abundant biopolymer in nature is one of the obvious choices. Cellulose, due to its properties that arise from the hierarchical structure, has been used for millennia by mankind although it is currently used, in the form of microfibers, mainly in the paper and pulp industry. However, many efforts are being directed towards retrieving even smaller cellulose constituents such as nanofibers and nanocrystals (i.e., nanocellulose), which can actually be used in high performance materials. In order to do so, a better understanding of the behavior and interactions between these novel nanomaterials are required. Moreover, the combination of nanocellulose with inorganic nanoparticles bears a great potential that can open the door to multifunctional materials based on a renewable component.

In this work, the anisotropic behavior, i.e., the formation of a chiral nematic phase, of cellulose nanocrystals (CNC) initially dispersed in aqueous media spanning a wide volume fraction range has been studied by small angle X-ray scattering (SAXS) and laser diffraction. The analysis shows that the twist angle between neighboring CNCs increased from ~1° up to ~4° as the CNC volume fraction increased from 2.5 to 6.5 vol%.

Also, the drying of an aqueous CNC droplet immersed in a binary toluene/ethanol mixture was studied and monitored in-situ by polarized video microscopy, where the influence of the water dissolution rate on the morphology of the resulting microbeads was investigated by scanning electron microscopy. The morphology of the microbeads depends not only on the drying speed but also on the initial starting CNC volume fraction. In this regard, the influence of the degrees of liquid crystallinity on the formation of a chiral nematic phase on films has also been studied.

Lastly, the fabrication and various properties of hybrids and composites prepared from cellulose nanofibers (CNF) and inorganic constituents are presented. The structure and chemistry of a museum sample of a traditional African textile (Bogolan) is analyzed and the chemical foundation of the dyeing method is outlined. This Bogolan dyeing method was used to pattern CNF films, and to study the details of how the surface-bound iron-tannin complexes are formed on the cellulose surface.

Also, the formation of transparent, hard and flexible films based on CNF-titania (anatase) nanoparticle hybrids was studied, where the influence of the composition of the hybrids on the optical and mechanical properties is discussed on the basis of results from electron microscopy, spectrophotometry and nanoindentation.

Place, publisher, year, edition, pages
Stockholm: Department of Materials and Environmental Chemistry (MMK), Stockholm University, 2015. 60 p.
National Category
Materials Chemistry
Research subject
Materials Chemistry
Identifiers
urn:nbn:se:su:diva-116517 (URN)978-91-7649-064-8 (ISBN)
Public defence
2015-05-29, Magnéli Hall, Arrhenius Laboratory, Svante Arrhenius Väg 16 B, Stockholm, 13:00 (English)
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Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 1: Submitted. Paper 2: Submitted. Paper 4: Manuscript.

Available from: 2015-05-07 Created: 2015-04-21 Last updated: 2015-10-27Bibliographically approved

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