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Chiral Nematic Structure of Cellulose Nanocrystal Suspensions and Films; Polarized Light and Atomic Force Microscopy

Department of Chemistry, McGill University, Pulp and Paper Building, 3420 University Street, Montreal, QC H3A-2A7, Canada
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Academic Editors: Aldo R. Boccaccini, Jung Kwon (John) Oh and Juergen Stampfl
Materials 2015, 8(11), 7873-7888; https://doi.org/10.3390/ma8115427
Received: 5 October 2015 / Revised: 4 November 2015 / Accepted: 10 November 2015 / Published: 18 November 2015
(This article belongs to the Section Biomaterials)
Cellulosic liquid crystalline solutions and suspensions form chiral nematic phases that show a rich variety of optical textures in the liquid crystalline state. These ordered structures may be preserved in solid films prepared by evaporation of solvent or suspending medium. Film formation from aqueous suspensions of cellulose nanocrystals (CNC) was investigated by polarized light microscopy, optical profilometry and atomic force microscopy (AFM). An attempt is made to interpret qualitatively the observed textures in terms of the orientation of the cellulose nanocrystals in the suspensions and films, and the changes in orientation caused by the evaporative process. Mass transfer within the evaporating droplet resulted in the formation of raised rings whose magnitude depended on the degree of pinning of the receding contact line. AFM of dry films at short length scales showed a radial orientation of the CNC at the free surface of the film, along with a radial height variation with a period of approximately P/2, ascribed to the anisotropic shrinkage of the chiral nematic structure. View Full-Text
Keywords: cellulose nanocrystals; chiral nematic order; polarized light microscopy; fingerprint texture; reflection colours; coffee-stain effect; sessile droplets; contact line pinning cellulose nanocrystals; chiral nematic order; polarized light microscopy; fingerprint texture; reflection colours; coffee-stain effect; sessile droplets; contact line pinning
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Gray, D.G.; Mu, X. Chiral Nematic Structure of Cellulose Nanocrystal Suspensions and Films; Polarized Light and Atomic Force Microscopy. Materials 2015, 8, 7873-7888.

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